diff --git a/.agents/notes/implemented/feature/2026-07-12-subagent-persona-tool-filter-and-depth.md b/.agents/notes/implemented/feature/2026-07-12-subagent-persona-tool-filter-and-depth.md
index 29f77364fa..0f42a547cf 100644
--- a/.agents/notes/implemented/feature/2026-07-12-subagent-persona-tool-filter-and-depth.md
+++ b/.agents/notes/implemented/feature/2026-07-12-subagent-persona-tool-filter-and-depth.md
@@ -49,9 +49,11 @@ The global registry remains live. A deny-only filter admits a later global name
 
 The depth limit bounds recursive delegation independently of tool visibility. A top-level agent has depth zero; an in-process child has its parent's validated depth plus one. `maxDepth` is an absolute non-negative safe integer, and a start rejects before child ownership begins when the derived child depth is greater than the cap.
 
-Every public entry validates the domain rather than relying on one model-facing configuration path. Negative values, fractions, negative zero, non-finite values, unsafe integers, malformed stored parent depth, and derived overflow all reject. Omitting the cap leaves depth unbounded by this mechanism.
+The effective parent depth is the greater of durable `SessionHeader.delegationDepth` and runtime `AgentOptions.subagentDepth`. An in-process child records its derived depth in the session header, and resume restores that header, so a restart cannot lower the recursion count.
 
-A deployment can combine depth and filtering. For example, it may keep the delegation tool visible at depth one but set `maxDepth: 1`, or deny the delegation tool entirely in children. Neither choice changes the provider's conversation-history behavior.
+Every public entry validates the domain rather than relying on one model-facing configuration path. Negative values, fractions, negative zero, non-finite values, unsafe integers, malformed stored parent depth, and derived overflow all reject. A direct `SubagentStartRequest` may omit the cap to leave depth unbounded; loader-resolved `dsh-tool-subagent` configuration instead defaults to `3`, accepts a numeric override, and uses explicit `'provider-managed'` to omit the cap for an out-of-process provider whose deployment owns its recursion budget. Three is a small finite default that still permits a root plus three descendant generations: the [SDK helper's generated subagent entries](../../../../packages/sdk/helper/src/features/builtin/index.ts) and [JSON-RPC example](../../../../examples/jsonrpc-agent/cordis.yml) use that general policy, while the shipped interactive ACP, headless, and REPL examples pin one. A numeric tool cap fails at provider mount when the provider lacks `depthLimit`.
+
+A deployment can combine depth and filtering, but the numeric cap does not synthesize a filter. The delegation tool stays visible at the cap because authorization may depend on runtime state; every attempted start checks the calling agent's current durable and runtime depth, and a rejected start returns an errored tool result without publishing a child. A deployment may separately deny delegation tools in children when its visibility policy is static. Neither choice changes the provider's conversation-history behavior.
 
 ### Capability gating keeps providers honest
 
@@ -83,10 +85,10 @@ A security design would need a separate authority representation, propagation ru
 
 **Hide only tool schemas.** Presentation-only filtering lets the model execute a tool that the prompt says does not exist through Code Mode or a forged call. One resolver governs both presentation and execution instead.
 
-**Use only tool filtering to stop recursion.** Removing the delegation tool is useful but provider-specific and does not protect direct service callers or alternate delegation tools. Absolute depth is an independent structural bound.
+**Encode the depth cap as an automatic tool filter.** A creation-time filter snapshots a decision that may depend on runtime state, affects only one configured tool name, and does not protect direct service callers or alternate delegation tools. The provider instead enforces the absolute cap at every start.
 
 ## Consequences
 
 Contributors can configure child role, visible global tools, and recursion without defining new providers. Capability checks fail before ownership starts, unpublished setup makes the first request consistent, and one tool resolver prevents presentation/execution drift.
 
-The cost is that deployments must understand live allow/deny behavior and the distinction between visibility and authority. Provider authors must advertise each supported control accurately, and in-process providers must install every requested contribution before publication. The controls deliberately do not solve security confinement or parent-to-child non-escalation.
+The cost is that deployments must understand live allow/deny behavior and the distinction between visibility and authority. A model may call a visible delegation tool after the current depth policy forbids another child and receive an error. Provider authors must advertise each supported control accurately, and in-process providers must install every requested contribution before publication. The controls deliberately do not solve security confinement or parent-to-child non-escalation.
diff --git a/docs/architecture.md b/docs/architecture.md
index 2e37f72c56..b3cacf4553 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -59,7 +59,7 @@ The shipped loop drains prompt-to-checkpoint work through plugin-visible service
 
 A **session** is an append-only log. Each ordinary **turn** claims one queued `send()` item; injection claims none. A claimed `send()` successor awaits the preceding claimed ordinary turn's checkpoint but may share its `running` interval ([decision](../.agents/notes/implemented/simplification/2026-07-17-one-send-one-turn.md)). A turn ends when model and plugins stop it. A **step** is one model request plus tools. Below ([sequence companion](agent-lifecycle.md)), quotes mark durable events; other names are extension points.
 
-Startup resolves identity. No id mints `<config-id>-session-<uuid>`; `sessionId` resumes or creates; `resumeSessionId` requires history. Active failures emit `agent-loop/config-start-failed(sessionId, error)`, so front doors reject work; teardown stays silent.
+No id mints `<config-id>-session-<uuid>`; `sessionId` resumes/creates; `resumeSessionId` needs history. Resume restores lineage, seeds, and delegation depth pre-publication. Failures emit `agent-loop/config-start-failed(sessionId, error)`; front doors reject; teardown stays silent.
 
 ### Turn Flow
 
diff --git a/docs/config-catalog.md b/docs/config-catalog.md
index e731070b6d..93820550fc 100644
--- a/docs/config-catalog.md
+++ b/docs/config-catalog.md
@@ -1105,8 +1105,7 @@ export interface Config {
   /**
    * Tool filter applied to every child. Filtered tools disappear from its
    * prompt and reject execution. Requires the provider's `toolFilter`
-   * capability; unknown names fail startup. Children otherwise see this tool,
-   * so deny it or set `maxDepth` to bound recursion.
+   * capability; unknown names fail startup.
    */
   toolFilter?: {
     /** Global tool names the child keeps; everything else is removed. */
@@ -1115,10 +1114,15 @@ export interface Config {
     deny?: string[]
   }
   /**
-   * Maximum child depth. Requires the provider's `depthLimit` capability and a
-   * non-negative safe integer. Omission is unbounded.
+   * Maximum child depth: a non-negative safe integer (default `3`; `0` forbids
+   * delegation entirely), or `'provider-managed'` to send no cap. A numeric cap
+   * requires the provider's `depthLimit` capability (mount fails loud
+   * otherwise). The provider checks the calling agent's current depth at every
+   * start; the tool remains model-visible so runtime policy owns rejection.
+   * `'provider-managed'` is for an out-of-process provider (ACP) whose
+   * recursion budget belongs to the child harness's own deployment.
    */
-  maxDepth?: number
+  maxDepth?: number | 'provider-managed'
 }
 ```
 
diff --git a/docs/cordis-catalog/events.md b/docs/cordis-catalog/events.md
index ae17230a7a..b78b395959 100644
--- a/docs/cordis-catalog/events.md
+++ b/docs/cordis-catalog/events.md
@@ -585,7 +585,7 @@ A ready child settled. Scope-filtered dispatch uses the same delegating parent c
 
 Types: [Scoped](../core-data-structures/scope.md) · [SubagentService](../core-data-structures/subagent.md)
 
-Source: [`packages/subagent/subagent/src/index.ts:112`](../../packages/subagent/subagent/src/index.ts)
+Source: [`packages/subagent/subagent/src/index.ts:139`](../../packages/subagent/subagent/src/index.ts)
 
 ### `subagent/provider-added` — emit
 
@@ -602,7 +602,7 @@ A provider became resolvable in the registry.
 
 Types: [SubagentProvider](../core-data-structures/subagent.md)
 
-Source: [`packages/subagent/subagent/src/index.ts:86`](../../packages/subagent/subagent/src/index.ts)
+Source: [`packages/subagent/subagent/src/index.ts:113`](../../packages/subagent/subagent/src/index.ts)
 
 ### `subagent/provider-removed` — emit
 
@@ -617,7 +617,7 @@ A provider left the registry. Accepted runs remain holder-owned.
 'subagent/provider-removed'(name: string): void
 ```
 
-Source: [`packages/subagent/subagent/src/index.ts:92`](../../packages/subagent/subagent/src/index.ts)
+Source: [`packages/subagent/subagent/src/index.ts:119`](../../packages/subagent/subagent/src/index.ts)
 
 ### `subagent/start` — emit
 
@@ -639,7 +639,7 @@ A provider established a ready child. For in-process providers, `ctx.agents.get(
 
 Types: [Scoped](../core-data-structures/scope.md) · [SubagentService](../core-data-structures/subagent.md)
 
-Source: [`packages/subagent/subagent/src/index.ts:103`](../../packages/subagent/subagent/src/index.ts)
+Source: [`packages/subagent/subagent/src/index.ts:130`](../../packages/subagent/subagent/src/index.ts)
 
 ## `system-prompt/*`
 
diff --git a/docs/cordis-catalog/services.md b/docs/cordis-catalog/services.md
index d1cd96afa3..94d181d110 100644
--- a/docs/cordis-catalog/services.md
+++ b/docs/cordis-catalog/services.md
@@ -216,7 +216,7 @@ roots(): Agent[]
 
 Types: [Agent](../core-data-structures/core.md) · [SessionId](../core-data-structures/core.md)
 
-Source: [`packages/core/agent/src/index.ts:217`](../../packages/core/agent/src/index.ts)
+Source: [`packages/core/agent/src/index.ts:223`](../../packages/core/agent/src/index.ts)
 
 ## `ctx.approval` — `ApprovalService`
 
@@ -718,9 +718,9 @@ Persistence is intentionally not implemented here — persistence plugins subscr
  * Create a session owned by the calling fiber: disposing that fiber stops
  * event notification and removes the session from the store. `options.seed`
  * populates the session with a copy of those events (replay/fork);
- * `options.meta` attaches creation metadata (validated absolute `cwd`,
- * `parentSession` lineage) as the immutable {@link SessionHeader} (the store
- * fills `version`/`id`/`createdAt`).
+ * `options.meta` attaches creation metadata (validated absolute `cwd`, seed
+ * and parent lineage, and delegation depth) as the immutable
+ * {@link SessionHeader} (the store fills `version`/`id`/`createdAt`).
  *
  * For an agent whose session must be torn down IN ORDER with its loop (so the
  * loop's final flush is captured before the store attachment ends), do NOT use this
@@ -832,7 +832,7 @@ fork(source: SessionForkSource, boundary?: number, childSessionId?: SessionId):
 
 Types: [CreateSessionOptions](../core-data-structures/persistence.md) · [Session](../core-data-structures/session.md) · [SessionId](../core-data-structures/core.md)
 
-Source: [`packages/core/session/src/index.ts:549`](../../packages/core/session/src/index.ts)
+Source: [`packages/core/session/src/index.ts:553`](../../packages/core/session/src/index.ts)
 
 ## `ctx.skills` — `SkillService`
 
@@ -946,7 +946,7 @@ async start(name: string, request: SubagentStartRequest): Promise<SubagentRun>
 
 Types: [SubagentProvider](../core-data-structures/subagent.md) · [SubagentRun](../core-data-structures/subagent.md) · [SubagentStartRequest](../core-data-structures/subagent.md)
 
-Source: [`packages/subagent/subagent/src/index.ts:153`](../../packages/subagent/subagent/src/index.ts)
+Source: [`packages/subagent/subagent/src/index.ts:180`](../../packages/subagent/subagent/src/index.ts)
 
 ## `ctx.systemPrompt` — `SystemPrompt`
 
diff --git a/docs/core-data-structures/persistence.md b/docs/core-data-structures/persistence.md
index 18ef172ef8..0c6eecd35f 100644
--- a/docs/core-data-structures/persistence.md
+++ b/docs/core-data-structures/persistence.md
@@ -60,12 +60,18 @@ interface SessionHeader {
    * boundary lets resume and replay distinguish parent history from child work.
    */
   readonly seedLength?: number
+  /**
+   * Delegation depth: absent (zero) for a top-level session, parent depth + 1
+   * for a subagent child. Persisted so a recursion budget survives restart and
+   * resume — a runtime-only depth would reset a resumed child to top-level.
+   */
+  readonly delegationDepth?: number
 }
 ```
 
 ## `CreateSessionOptions` — seeding and metadata
 
-Creating a `Session` through the store takes a `seed` (replay/fork an existing event log) and `meta` (the storage-level fields the store folds into a `SessionHeader`). The store fills in `version`/`id` and defaults `createdAt`; the caller supplies the validated absolute `cwd`, the `parentSession` lineage, the `seedLength` seed boundary, and — only when reconstructing a persisted session — the original `createdAt` to preserve it.
+Creating a `Session` through the store takes a `seed` (replay/fork an existing event log) and `meta` (the storage-level fields the store folds into a `SessionHeader`). The store fills in `version`/`id` and defaults `createdAt`; the caller supplies the validated absolute `cwd`, the `parentSession` lineage, the `seedLength` seed boundary, the `delegationDepth`, and — only when reconstructing a persisted session — the original `createdAt` to preserve it.
 
 ```ts type-equiv
 /**
@@ -85,6 +91,7 @@ interface CreateSessionOptions {
     readonly parentSession?: SessionId
     readonly createdAt?: number
     readonly seedLength?: number
+    readonly delegationDepth?: number
   }
 }
 ```
diff --git a/docs/core-data-structures/subagent.md b/docs/core-data-structures/subagent.md
index 54e79aca68..bd4324e697 100644
--- a/docs/core-data-structures/subagent.md
+++ b/docs/core-data-structures/subagent.md
@@ -237,5 +237,5 @@ interface SubagentProvider {
 
 The spawn and fork backends create an ordinary agent through `parent.ctx`, pass cancellation into core creation, and dispose through `AgentHandle`. Provider removal blocks new starts without revoking accepted runs. Each child gets a new flat scope rather than inheriting parent registrations. Depth and fork seeding reuse existing agent and session vocabulary:
 
-- **Delegation depth** is a merge-extensible `AgentOptions.subagentDepth` field (`0` for a top-level agent, parent + 1 for a child). Only `undefined` means top level; every stored present value must be a non-negative safe integer. The seam owns it — the loop neither sets nor reads it — so a nested spawn validates its parent's stored depth, rejects a derived child depth outside the safe-integer domain, and applies a defined absolute `request.maxDepth` cap to that child.
+- **Delegation depth** is durable `SessionHeader.delegationDepth` plus the merge-extensible runtime field `AgentOptions.subagentDepth`; absence means top-level depth zero, and the greater present value is authoritative. The seam owns both fields — the loop neither sets nor reads them — so an in-process child persists parent depth + 1, resume cannot lower it, and every start rejects a derived depth outside the safe-integer domain or above a defined absolute `request.maxDepth` cap.
 - **Fork seeding** uses `CreateAgentOptions.seed` (a `SessionEvent[]` prefix threaded through `AgentLoop.createAgent` → `ctx.sessions.prepare({ seed })`, the same primitive `resume` uses). The fork backend passes a *balanced completed-turn prefix* of the parent's log — the parent's events up to and including its last `turn/end` — so the seed is contiguous-from-0 and the [invariants](../../packages/support/invariants) replay accepts it (the in-flight, unbalanced turn is excluded).
diff --git a/docs/event-producer-consumer.md b/docs/event-producer-consumer.md
index c1ec91e378..0a931c38f2 100644
--- a/docs/event-producer-consumer.md
+++ b/docs/event-producer-consumer.md
@@ -32,10 +32,10 @@ This matrix shows which packages dispatch each harness-owned event and which pac
 | `session/disposed` | `emit` | [`packages/core/session/src/index.ts:57`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`events.dispatch`) | [`agent-loop`](../packages/core/agent-loop), [`session-persistence`](../packages/session-persistence/session-persistence) |
 | `session/event` | `emit` | [`packages/core/session/src/index.ts:69`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`events.dispatch`) | [`acp`](../packages/ui/acp), [`cli-demo`](../packages/examples/cli-demo), [`invariants`](../packages/support/invariants), [`jsonrpc`](../packages/ui/jsonrpc), [`session-persistence`](../packages/session-persistence/session-persistence), [`token-meter`](../packages/llm/token-meter), [`tui`](../packages/ui/tui), [`workspace-context`](../packages/context/workspace-context) |
 | `session/flush` | `parallel` | [`packages/core/session/src/index.ts:79`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`events.dispatch`) | [`session-persistence`](../packages/session-persistence/session-persistence) |
-| `subagent/end` | `emit` | [`packages/subagent/subagent/src/index.ts:112`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`hooks-claude`](../packages/hooks/hooks-claude), [`jsonrpc`](../packages/ui/jsonrpc) |
-| `subagent/provider-added` | `emit` | [`packages/subagent/subagent/src/index.ts:86`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`emit`) | [`tool-subagent`](../packages/subagent/tool-subagent) |
-| `subagent/provider-removed` | `emit` | [`packages/subagent/subagent/src/index.ts:92`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`tool-subagent`](../packages/subagent/tool-subagent) |
-| `subagent/start` | `emit` | [`packages/subagent/subagent/src/index.ts:103`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`hooks-claude`](../packages/hooks/hooks-claude) |
+| `subagent/end` | `emit` | [`packages/subagent/subagent/src/index.ts:139`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`hooks-claude`](../packages/hooks/hooks-claude), [`jsonrpc`](../packages/ui/jsonrpc) |
+| `subagent/provider-added` | `emit` | [`packages/subagent/subagent/src/index.ts:113`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`emit`) | [`tool-subagent`](../packages/subagent/tool-subagent) |
+| `subagent/provider-removed` | `emit` | [`packages/subagent/subagent/src/index.ts:119`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`tool-subagent`](../packages/subagent/tool-subagent) |
+| `subagent/start` | `emit` | [`packages/subagent/subagent/src/index.ts:130`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`hooks-claude`](../packages/hooks/hooks-claude) |
 | `system-prompt/assemble` | `waterfall` | [`packages/core/system-prompt/src/index.ts:27`](../packages/core/system-prompt/src/index.ts) | [`system-prompt`](../packages/core/system-prompt) (`waterfall`) | [`acp`](../packages/ui/acp) |
 | `system-prompt/change` | `emit` | [`packages/core/system-prompt/src/index.ts:33`](../packages/core/system-prompt/src/index.ts) | [`system-prompt`](../packages/core/system-prompt) (`emit`) | - |
 | `tools/change` | `emit` | [`packages/core/tools/src/index.ts:116`](../packages/core/tools/src/index.ts) | [`tools`](../packages/core/tools) (`emit`) | - |
diff --git a/docs/glossary.md b/docs/glossary.md
index 5392773dc9..0bed6fc56e 100644
--- a/docs/glossary.md
+++ b/docs/glossary.md
@@ -14,4 +14,4 @@ FIXME(glossary-completeness): Expand this glossary before the first release so i
 - **shadowing** — most-specific-wins name resolution: a scoped tool/section/variable replaces its same-named global twin for that scope alone. The per-agent persona and per-agent tool-variant mechanism.
 - **restriction / scope-local registration** — a restriction (`tools.restrict`) filters the GLOBAL tool surface for one scope (compose by intersection); scope-local registrations are merged after that filter. A filtered-away global tool is absent from the prompt AND refuses execution, indistinguishably from a nonexistent one.
 - **setup window** — the creation slot where a creator composes an agent's scoped world (`CreateAgentOptions.setup`): after the scope and agent object exist but before the agent or session is published, `agent/session-start` fires, or the first prompt is assembled. Setup registers; it never drives the agent.
-- **lineage** — parent/child facts carried as data (`parentSession`, `subagentDepth`); never affects visibility. <a id="lineage"></a>
+- **lineage** — parent/child facts carried as data (`parentSession`, durable `delegationDepth`, runtime `subagentDepth`); never affects visibility. <a id="lineage"></a>
diff --git a/docs/persistence-catalog.md b/docs/persistence-catalog.md
index 6ab6f5f1d4..209fb04d1c 100644
--- a/docs/persistence-catalog.md
+++ b/docs/persistence-catalog.md
@@ -79,7 +79,7 @@ export type SessionEvent<T extends SessionEventType = SessionEventType> = {
 }[T]
 ```
 
-Sources: [`packages/core/session/src/types.ts:256`](../packages/core/session/src/types.ts) · [`packages/core/session/src/types.ts:263`](../packages/core/session/src/types.ts) · [`packages/core/session/src/types.ts:293`](../packages/core/session/src/types.ts) · [`packages/core/session/src/types.ts:325`](../packages/core/session/src/types.ts)
+Sources: [`packages/core/session/src/types.ts:263`](../packages/core/session/src/types.ts) · [`packages/core/session/src/types.ts:270`](../packages/core/session/src/types.ts) · [`packages/core/session/src/types.ts:300`](../packages/core/session/src/types.ts) · [`packages/core/session/src/types.ts:332`](../packages/core/session/src/types.ts)
 
 ## Events
 
@@ -151,7 +151,7 @@ Source: [`packages/ui/user-approval/src/index.ts:68`](../packages/ui/user-approv
 
 Types: [StreamChunk](core-data-structures/llm-streaming.md)
 
-Source: [`packages/core/session/src/types.ts:220`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:227`](../packages/core/session/src/types.ts)
 
 #### `assistant/message` — surface
 
@@ -167,7 +167,7 @@ Source: [`packages/core/session/src/types.ts:220`](../packages/core/session/src/
 
 Types: [ContentBlock](core-data-structures/core.md) · [TokenUsage](core-data-structures/llm-streaming.md)
 
-Source: [`packages/core/session/src/types.ts:227`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:234`](../packages/core/session/src/types.ts)
 
 ### `compact/*`
 
@@ -246,7 +246,7 @@ Source: [`packages/compact/compact/src/types.ts:22`](../packages/compact/compact
 
 Types: [ContentBlock](core-data-structures/core.md) · [MessageSource](core-data-structures/core.md)
 
-Source: [`packages/core/session/src/types.ts:214`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:221`](../packages/core/session/src/types.ts)
 
 ### `hook/*`
 
@@ -324,7 +324,7 @@ Source: [`packages/ui/permission/src/index.ts:36`](../packages/ui/permission/src
 
 Types: [ContentBlock](core-data-structures/core.md) · [MessageSource](core-data-structures/core.md)
 
-Source: [`packages/core/session/src/types.ts:202`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:209`](../packages/core/session/src/types.ts)
 
 ### `request/*`
 
@@ -338,7 +338,7 @@ Source: [`packages/core/session/src/types.ts:202`](../packages/core/session/src/
 'request/header': { header: EpochHeader; reason: RequestHeaderReason }
 ```
 
-Source: [`packages/core/session/src/types.ts:252`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:259`](../packages/core/session/src/types.ts)
 
 ### `sandbox/*`
 
@@ -369,7 +369,7 @@ Source: [`packages/sandbox/sandbox-policy/src/session-mode.ts:34`](../packages/s
 
 Types: [ContentBlock](core-data-structures/core.md) · [MessageSource](core-data-structures/core.md)
 
-Source: [`packages/core/session/src/types.ts:245`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:252`](../packages/core/session/src/types.ts)
 
 ### `step/*`
 
@@ -380,7 +380,7 @@ Source: [`packages/core/session/src/types.ts:245`](../packages/core/session/src/
 'step/end': { turn: number; step: number }
 ```
 
-Source: [`packages/core/session/src/types.ts:195`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:202`](../packages/core/session/src/types.ts)
 
 #### `step/start` — log-only
 
@@ -389,7 +389,7 @@ Source: [`packages/core/session/src/types.ts:195`](../packages/core/session/src/
 'step/start': { turn: number; step: number }
 ```
 
-Source: [`packages/core/session/src/types.ts:193`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:200`](../packages/core/session/src/types.ts)
 
 ### `todo/*`
 
@@ -402,7 +402,7 @@ Source: [`packages/core/session/src/types.ts:193`](../packages/core/session/src/
 
 Types: [TodoItem](core-data-structures/session.md)
 
-Source: [`packages/core/session/src/types.ts:247`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:254`](../packages/core/session/src/types.ts)
 
 ### `tool/*`
 
@@ -419,7 +419,7 @@ Source: [`packages/core/session/src/types.ts:247`](../packages/core/session/src/
 
 Types: [CallId](core-data-structures/core.md)
 
-Source: [`packages/core/session/src/types.ts:233`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:240`](../packages/core/session/src/types.ts)
 
 #### `tool/code-dispatch` — log-only
 
@@ -463,7 +463,7 @@ Source: [`packages/core/tools/src/code-mode.ts:34`](../packages/core/tools/src/c
 
 Types: [CallId](core-data-structures/core.md) · [ContentBlock](core-data-structures/core.md)
 
-Source: [`packages/core/session/src/types.ts:243`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:250`](../packages/core/session/src/types.ts)
 
 ### `turn/*`
 
@@ -481,7 +481,7 @@ Source: [`packages/core/session/src/types.ts:243`](../packages/core/session/src/
 
 Types: [TurnEndReason](core-data-structures/session.md)
 
-Source: [`packages/core/session/src/types.ts:191`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:198`](../packages/core/session/src/types.ts)
 
 #### `turn/start` — log-only
 
@@ -497,7 +497,7 @@ Source: [`packages/core/session/src/types.ts:191`](../packages/core/session/src/
 
 Types: [TurnTrigger](core-data-structures/session.md)
 
-Source: [`packages/core/session/src/types.ts:184`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:191`](../packages/core/session/src/types.ts)
 
 ### `user/*`
 
@@ -510,4 +510,4 @@ Source: [`packages/core/session/src/types.ts:184`](../packages/core/session/src/
 
 Types: [ContentBlock](core-data-structures/core.md) · [MessageSource](core-data-structures/core.md)
 
-Source: [`packages/core/session/src/types.ts:197`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:204`](../packages/core/session/src/types.ts)
diff --git a/examples/acp-agent/cordis.yml b/examples/acp-agent/cordis.yml
index bcdcb75f73..b2ad545fe7 100644
--- a/examples/acp-agent/cordis.yml
+++ b/examples/acp-agent/cordis.yml
@@ -94,12 +94,14 @@
   config:
     provider: spawn
     toolName: subagent
+    maxDepth: 1
 
 - id: tool-subagent-fork
   name: '@deepseek-ai/dsh-tool-subagent'
   config:
     provider: fork
     toolName: subagent_fork
+    maxDepth: 1
 
 
 # The worker-thread workflow engine fans a model-written JavaScript script's
diff --git a/examples/acp-agent/depth-two.cordis.snapshot.yml b/examples/acp-agent/depth-two.cordis.snapshot.yml
new file mode 100644
index 0000000000..16aa6f587c
--- /dev/null
+++ b/examples/acp-agent/depth-two.cordis.snapshot.yml
@@ -0,0 +1,36 @@
+# Keyless counterpart to depth-two.cordis.yml: apply the depth patch and replace
+# the live adapter with per-session replay.
+- id: base
+  name: '@cordisjs/plugin-include'
+  config:
+    path: ./cordis.yml
+    patches:
+      - id: llm-deepseek
+        name: '@deepseek-ai/dsh-llm-deepseek'
+        disabled: true
+      - id: sandbox
+        name: '@deepseek-ai/dsh-sandbox-local'
+        config:
+          runnerCommand:
+            - bash
+            - -c
+            - while [ "$1" != "--" ]; do shift; done; shift; exec "$@"
+            - passthrough-runner
+          runnerFailureSignatures:
+            - 'passthrough-runner: profile rejected'
+      - id: tool-subagent
+        name: '@deepseek-ai/dsh-tool-subagent'
+        config:
+          provider: spawn
+          toolName: subagent
+          maxDepth: 2
+      - insert:
+          - id: llm-replay
+            name: '@deepseek-ai/dsh-llm-replay'
+            config:
+              providers:
+                - id: deepseek
+                  name: DeepSeek
+                  models:
+                    - id: deepseek-v4-flash
+                    - id: deepseek-v4-pro
diff --git a/examples/acp-agent/depth-two.cordis.yml b/examples/acp-agent/depth-two.cordis.yml
new file mode 100644
index 0000000000..25b0ee8e38
--- /dev/null
+++ b/examples/acp-agent/depth-two.cordis.yml
@@ -0,0 +1,13 @@
+# Depth-limit snapshot overlay: keep the default composition and allow two
+# generations of spawn children before runtime enforcement rejects another.
+- id: base
+  name: '@cordisjs/plugin-include'
+  config:
+    path: ./cordis.yml
+    patches:
+      - id: tool-subagent
+        name: '@deepseek-ai/dsh-tool-subagent'
+        config:
+          provider: spawn
+          toolName: subagent
+          maxDepth: 2
diff --git a/examples/acp-agent/tests/acp.snapshot.ts b/examples/acp-agent/tests/acp.snapshot.ts
index 792788245d..88ae18222c 100644
--- a/examples/acp-agent/tests/acp.snapshot.ts
+++ b/examples/acp-agent/tests/acp.snapshot.ts
@@ -30,6 +30,7 @@ const BOTH_MODE_CONFIG = fileURLToPath(new URL('../both-mode.cordis.yml', import
 const WORKSPACE_CONTEXT_CONFIG = fileURLToPath(new URL('../workspace-context.cordis.yml', import.meta.url))
 const ADVANCED_CONFIG = fileURLToPath(new URL('../advanced.cordis.yml', import.meta.url))
 const FS_CONFIG = fileURLToPath(new URL('../fs.cordis.yml', import.meta.url))
+const DEPTH_TWO_CONFIG = fileURLToPath(new URL('../depth-two.cordis.yml', import.meta.url))
 
 function snapshotModeFromEnv(value: string | undefined): SnapshotSuiteOptions['mode'] {
   switch (value) {
@@ -109,6 +110,13 @@ const SCENARIOS: Scenario[] = [
   { name: 'subagent-multi', hasModelTurn: true, recorded: true },
   { name: 'subagent-fork', hasModelTurn: true, recorded: true },
   { name: 'subagent-mixed', hasModelTurn: true, recorded: true },
+  {
+    name: 'subagent-depth-two-rejection',
+    hasModelTurn: true,
+    recorded: false,
+    overridden: true,
+    configPath: DEPTH_TWO_CONFIG,
+  },
   // The workflow tool: the model writes a one-child orchestration script; the
   // child runs as a spawn subagent under the worker-thread engine (its session is the
   // child fixture), and the tool result carries the script's return value.
diff --git a/examples/acp-agent/tests/fixtures/live-mode-switching-2026-07-07.session.jsonl b/examples/acp-agent/tests/fixtures/live-mode-switching-2026-07-07.session.jsonl
index 0852ef7513..10ffb8c507 100644
--- a/examples/acp-agent/tests/fixtures/live-mode-switching-2026-07-07.session.jsonl
+++ b/examples/acp-agent/tests/fixtures/live-mode-switching-2026-07-07.session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"ed16a7e7-a76f-459f-b889-d4c424d66ef6","createdAt":1783421406247,"cwd":"/Users/wwl/workspace/deepseek-harness"}
+{"type":"session","version":0,"id":"ed16a7e7-a76f-459f-b889-d4c424d66ef6","createdAt":1783421406247,"cwd":"/Users/wwl/workspace/deepseek-harness","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783421410388,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783421410388,"data":{"content":[{"type":"text","text":"你好"}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783421410389,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/advanced-toolchain/session.1.jsonl b/examples/acp-agent/tests/snapshots/advanced-toolchain/session.1.jsonl
index 25a6f76411..26519d458e 100644
--- a/examples/acp-agent/tests/snapshots/advanced-toolchain/session.1.jsonl
+++ b/examples/acp-agent/tests/snapshots/advanced-toolchain/session.1.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"22222222-2222-4222-8222-222222222222","createdAt":1783950001000,"cwd":"/tmp/advanced-acp","parentSession":"11111111-1111-4111-8111-111111111111"}
+{"type":"session","version":0,"id":"22222222-2222-4222-8222-222222222222","createdAt":1783950001000,"cwd":"/tmp/advanced-acp","parentSession":"11111111-1111-4111-8111-111111111111","delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783957884563,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783957884563,"data":{"content":[{"type":"text","text":"Reply with exactly DIRECT_CHILD_OK and nothing else."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783957884564,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/advanced-toolchain/session.2.jsonl b/examples/acp-agent/tests/snapshots/advanced-toolchain/session.2.jsonl
index 45d9043a4a..9daa8958dc 100644
--- a/examples/acp-agent/tests/snapshots/advanced-toolchain/session.2.jsonl
+++ b/examples/acp-agent/tests/snapshots/advanced-toolchain/session.2.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"33333333-3333-4333-8333-333333333333","createdAt":1783950002000,"cwd":"/tmp/advanced-acp","parentSession":"11111111-1111-4111-8111-111111111111"}
+{"type":"session","version":0,"id":"33333333-3333-4333-8333-333333333333","createdAt":1783950002000,"cwd":"/tmp/advanced-acp","parentSession":"11111111-1111-4111-8111-111111111111","delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783957884700,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783957884700,"data":{"content":[{"type":"text","text":"Reply with exactly WORKFLOW_CHILD_OK and nothing else."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783957884700,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/advanced-toolchain/session.jsonl b/examples/acp-agent/tests/snapshots/advanced-toolchain/session.jsonl
index 39f867984a..46c8e41257 100644
--- a/examples/acp-agent/tests/snapshots/advanced-toolchain/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/advanced-toolchain/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"11111111-1111-4111-8111-111111111111","createdAt":1783950000000,"cwd":"/tmp/advanced-acp"}
+{"type":"session","version":0,"id":"11111111-1111-4111-8111-111111111111","createdAt":1783950000000,"cwd":"/tmp/advanced-acp","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783957884479,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783957884479,"data":{"content":[{"type":"text","text":"Run this advanced flow exactly once: mount a no-op Cordis plugin named snapshot-marker; use run_code to inspect the live dynamic mounts through tools.cordis_inspect; delegate once to a direct spawn child; run one workflow that delegates to another spawn child; unmount dyn-1; then reply with exactly ADVANCED_ACP_OK."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783957884486,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/bash-spill/session.jsonl b/examples/acp-agent/tests/snapshots/bash-spill/session.jsonl
index 853b446f81..65f92c4916 100644
--- a/examples/acp-agent/tests/snapshots/bash-spill/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/bash-spill/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}"}
+{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":0,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":0,"data":{"content":[{"type":"text","text":"Use the bash tool to print a large deterministic output, then reply DONE."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":0,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/both-mode-turn/session.jsonl b/examples/acp-agent/tests/snapshots/both-mode-turn/session.jsonl
index 0ee3e67e2b..6b704c5bcd 100644
--- a/examples/acp-agent/tests/snapshots/both-mode-turn/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/both-mode-turn/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"bcd7e943-7b84-4264-82d0-f64e50d0d7ce","createdAt":1783611774317,"cwd":"/var/folders/2c/psb0_fmx7hbgz558xjt_f0l00000gn/T/acp-snap-cwd-52lrTl"}
+{"type":"session","version":0,"id":"bcd7e943-7b84-4264-82d0-f64e50d0d7ce","createdAt":1783611774317,"cwd":"/var/folders/2c/psb0_fmx7hbgz558xjt_f0l00000gn/T/acp-snap-cwd-52lrTl","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783611774323,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783611774323,"data":{"content":[{"type":"text","text":"Call the run_code tool (NOT the native bash tool directly) with a program that runs exactly `echo BOTH_OK` via tools.bash and returns its output. Then reply with that output only and stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783611774324,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/cancel-tool-calls/session.jsonl b/examples/acp-agent/tests/snapshots/cancel-tool-calls/session.jsonl
index e6d18515a6..cdb76be163 100644
--- a/examples/acp-agent/tests/snapshots/cancel-tool-calls/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/cancel-tool-calls/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}"}
+{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1784437195072,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1784437195072,"data":{"content":[{"type":"text","text":"Run two shell commands: wait for cancellation, then write skipped.txt."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1784437195076,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/cancel/session.jsonl b/examples/acp-agent/tests/snapshots/cancel/session.jsonl
index 347951db62..44e8ac136c 100644
--- a/examples/acp-agent/tests/snapshots/cancel/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/cancel/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}"}
+{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":0,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":0,"data":{"content":[{"type":"text","text":"Start a long task; this turn will be cancelled mid-stream."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":0,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/code-mode-turn/session.jsonl b/examples/acp-agent/tests/snapshots/code-mode-turn/session.jsonl
index 0fe57055e8..8ee160ba26 100644
--- a/examples/acp-agent/tests/snapshots/code-mode-turn/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/code-mode-turn/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"94cd1ae4-e1d1-4ec8-9d27-50a1f849b6b3","createdAt":1783611771392,"cwd":"/var/folders/2c/psb0_fmx7hbgz558xjt_f0l00000gn/T/acp-snap-cwd-BteTVR"}
+{"type":"session","version":0,"id":"94cd1ae4-e1d1-4ec8-9d27-50a1f849b6b3","createdAt":1783611771392,"cwd":"/var/folders/2c/psb0_fmx7hbgz558xjt_f0l00000gn/T/acp-snap-cwd-BteTVR","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783611771394,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783611771394,"data":{"content":[{"type":"text","text":"Using ONE run_code program: call the bash tool twice — exactly `echo CODE_ONE` then exactly `echo CODE_TWO` — and return the two outputs joined with a plus sign. Then reply with that joined string only and stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783611771396,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/code-mode-workspace-context/session.jsonl b/examples/acp-agent/tests/snapshots/code-mode-workspace-context/session.jsonl
index a20dbcd999..4f72ffa498 100644
--- a/examples/acp-agent/tests/snapshots/code-mode-workspace-context/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/code-mode-workspace-context/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"65fbb8a6-624c-4d6a-bf5d-a7a7d14f2b49","createdAt":1783921765266,"cwd":"/var/folders/_g/59jgff8x2gqd39f5vy1wnbfc0000gn/T/acp-snap-cwd-uorU26"}
+{"type":"session","version":0,"id":"65fbb8a6-624c-4d6a-bf5d-a7a7d14f2b49","createdAt":1783921765266,"cwd":"/var/folders/_g/59jgff8x2gqd39f5vy1wnbfc0000gn/T/acp-snap-cwd-uorU26","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783921765269,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783921765269,"data":{"content":[{"type":"text","text":"Using ONE run_code program, call tools.read on nested/task.txt. After the program finishes, answer the workspace handshake question using the newly discovered instructions: What is the Code Mode workspace handshake?"}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783921765275,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/config-options/session.jsonl b/examples/acp-agent/tests/snapshots/config-options/session.jsonl
index a6f73319bc..63f2775383 100644
--- a/examples/acp-agent/tests/snapshots/config-options/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/config-options/session.jsonl
@@ -1 +1 @@
-{"type":"session","version":0,"id":"00000000-0000-0000-0000-000000000000","createdAt":0}
+{"type":"session","version":0,"id":"00000000-0000-0000-0000-000000000000","createdAt":0,"delegationDepth":0}
diff --git a/examples/acp-agent/tests/snapshots/cordis-inspect-jsdoc/session.jsonl b/examples/acp-agent/tests/snapshots/cordis-inspect-jsdoc/session.jsonl
index dc9e4a844a..207f8d8cc3 100644
--- a/examples/acp-agent/tests/snapshots/cordis-inspect-jsdoc/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/cordis-inspect-jsdoc/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"22222222-2222-4222-8222-222222222222","createdAt":1783951000000,"cwd":"/tmp/cordis-inspect-jsdoc"}
+{"type":"session","version":0,"id":"22222222-2222-4222-8222-222222222222","createdAt":1783951000000,"cwd":"/tmp/cordis-inspect-jsdoc","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1784449176717,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1784449176718,"data":{"content":[{"type":"text","text":"Inspect the exact tools service API and tools/pre-execute event with cordis_inspect, then reply with exactly CORDIS_INSPECT_JSDOC_OK."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1784449176720,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/error-finish/session.jsonl b/examples/acp-agent/tests/snapshots/error-finish/session.jsonl
index f0ef4267ac..6b6c44ebff 100644
--- a/examples/acp-agent/tests/snapshots/error-finish/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/error-finish/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}"}
+{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":0,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":0,"data":{"content":[{"type":"text","text":"This prompt triggers a recorded provider error."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":0,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/escalation-approved/session.jsonl b/examples/acp-agent/tests/snapshots/escalation-approved/session.jsonl
index b3931b079b..354a014a63 100644
--- a/examples/acp-agent/tests/snapshots/escalation-approved/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/escalation-approved/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"f3cbd087-fb45-4b32-b0f2-3082d65bfcb4","createdAt":1783860675270,"cwd":"/var/folders/2g/b32ct0qn1d728l_v6tdkjytr0000gn/T/acp-snap-cwd-cbBLh2"}
+{"type":"session","version":0,"id":"f3cbd087-fb45-4b32-b0f2-3082d65bfcb4","createdAt":1783860675270,"cwd":"/var/folders/2g/b32ct0qn1d728l_v6tdkjytr0000gn/T/acp-snap-cwd-cbBLh2","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783860675271,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"permission/preset","seq":1,"time":1783962245380,"data":{"preset":"workspace-write"}}
 {"type":"sandbox/mode","seq":2,"time":1784518116517,"data":{"mode":"workspace-write"}}
diff --git a/examples/acp-agent/tests/snapshots/escalation-rejected/session.jsonl b/examples/acp-agent/tests/snapshots/escalation-rejected/session.jsonl
index af1afd3c4a..ff6d1187b3 100644
--- a/examples/acp-agent/tests/snapshots/escalation-rejected/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/escalation-rejected/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"d692fe7f-7079-4ee4-8b06-f44fd026d4ea","createdAt":1783860679475,"cwd":"/var/folders/2g/b32ct0qn1d728l_v6tdkjytr0000gn/T/acp-snap-cwd-Hn29Od"}
+{"type":"session","version":0,"id":"d692fe7f-7079-4ee4-8b06-f44fd026d4ea","createdAt":1783860679475,"cwd":"/var/folders/2g/b32ct0qn1d728l_v6tdkjytr0000gn/T/acp-snap-cwd-Hn29Od","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783860679476,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"permission/preset","seq":1,"time":1783962246267,"data":{"preset":"workspace-write"}}
 {"type":"sandbox/mode","seq":2,"time":1784518117237,"data":{"mode":"workspace-write"}}
diff --git a/examples/acp-agent/tests/snapshots/fs-edit/session.jsonl b/examples/acp-agent/tests/snapshots/fs-edit/session.jsonl
index 00587e34c2..25992426b8 100644
--- a/examples/acp-agent/tests/snapshots/fs-edit/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/fs-edit/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"736c4bd8-41bd-43fb-9030-b4df3b2a4f83","createdAt":1783352084735,"cwd":"/tmp/acp-snap-cwd-0BxHdV"}
+{"type":"session","version":0,"id":"736c4bd8-41bd-43fb-9030-b4df3b2a4f83","createdAt":1783352084735,"cwd":"/tmp/acp-snap-cwd-0BxHdV","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352084740,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352084740,"data":{"content":[{"type":"text","text":"First use the read tool to read config.txt in the current directory. Then use the edit tool (NOT bash) to replace the literal text DEBUG with RELEASE in that file. Then reply with exactly the single word DONE."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352084742,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/fs-escalation-approved/session.jsonl b/examples/acp-agent/tests/snapshots/fs-escalation-approved/session.jsonl
index f796b0b473..54601f5354 100644
--- a/examples/acp-agent/tests/snapshots/fs-escalation-approved/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/fs-escalation-approved/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"977a4820-f609-4b48-9039-adcdd921c5fe","createdAt":1784045702340,"cwd":"/var/folders/2g/b32ct0qn1d728l_v6tdkjytr0000gn/T/acp-snap-cwd-vmEGzd"}
+{"type":"session","version":0,"id":"977a4820-f609-4b48-9039-adcdd921c5fe","createdAt":1784045702340,"cwd":"/var/folders/2g/b32ct0qn1d728l_v6tdkjytr0000gn/T/acp-snap-cwd-vmEGzd","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1784045702342,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"permission/preset","seq":1,"time":1784045702343,"data":{"preset":"workspace-write"}}
 {"type":"sandbox/mode","seq":2,"time":1784045702343,"data":{"mode":"workspace-write"}}
diff --git a/examples/acp-agent/tests/snapshots/fs-policy-reject/session.jsonl b/examples/acp-agent/tests/snapshots/fs-policy-reject/session.jsonl
index 03a64d2e39..66efd5f934 100644
--- a/examples/acp-agent/tests/snapshots/fs-policy-reject/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/fs-policy-reject/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"b3292503-2c3d-4677-804d-1ed6802a4bc5","createdAt":1783611702544,"cwd":"/var/folders/2c/psb0_fmx7hbgz558xjt_f0l00000gn/T/acp-snap-cwd-QzoqnB"}
+{"type":"session","version":0,"id":"b3292503-2c3d-4677-804d-1ed6802a4bc5","createdAt":1783611702544,"cwd":"/var/folders/2c/psb0_fmx7hbgz558xjt_f0l00000gn/T/acp-snap-cwd-QzoqnB","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783611702550,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783611702550,"data":{"content":[{"type":"text","text":"Do NOT use the read tool and do NOT use bash or shell commands. Immediately use the edit tool to replace the literal text blue with green in settings.txt in the current directory. Do not read the file first. After the tool result, reply with exactly the single word DONE."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783611702550,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/fs-read-window/session.jsonl b/examples/acp-agent/tests/snapshots/fs-read-window/session.jsonl
index e587011cfd..f0e1f170ac 100644
--- a/examples/acp-agent/tests/snapshots/fs-read-window/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/fs-read-window/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"b5639b9d-99a9-49e4-83da-77e6caa702be","createdAt":1783352099834,"cwd":"/tmp/acp-snap-cwd-N9HCkt"}
+{"type":"session","version":0,"id":"b5639b9d-99a9-49e4-83da-77e6caa702be","createdAt":1783352099834,"cwd":"/tmp/acp-snap-cwd-N9HCkt","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352099838,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352099839,"data":{"content":[{"type":"text","text":"Use the read tool (NOT bash) with offset 5 and limit 4 to read lines 5 through 8 of big.txt in the current directory. Then reply with exactly the single word DONE."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352099840,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/fs-read/session.jsonl b/examples/acp-agent/tests/snapshots/fs-read/session.jsonl
index 81737364f8..5582896174 100644
--- a/examples/acp-agent/tests/snapshots/fs-read/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/fs-read/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"a57f852d-d476-4716-a380-8a1116e4d905","createdAt":1783352072464,"cwd":"/tmp/acp-snap-cwd-PEETkS"}
+{"type":"session","version":0,"id":"a57f852d-d476-4716-a380-8a1116e4d905","createdAt":1783352072464,"cwd":"/tmp/acp-snap-cwd-PEETkS","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352072468,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352072469,"data":{"content":[{"type":"text","text":"Use the read tool (NOT bash) to read the file greeting.txt in the current directory, then reply with exactly the single word DONE."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352072470,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/fs-terminal-card/session.jsonl b/examples/acp-agent/tests/snapshots/fs-terminal-card/session.jsonl
index e53f4b3da3..5c3bba5676 100644
--- a/examples/acp-agent/tests/snapshots/fs-terminal-card/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/fs-terminal-card/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"e128dda9-ed11-4868-8266-0ef90d03c3d6","createdAt":1783352050748,"cwd":"/tmp/acp-snap-cwd-mrFUuk"}
+{"type":"session","version":0,"id":"e128dda9-ed11-4868-8266-0ef90d03c3d6","createdAt":1783352050748,"cwd":"/tmp/acp-snap-cwd-mrFUuk","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352050753,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352050753,"data":{"content":[{"type":"text","text":"Use the bash tool to run exactly: echo TERMINAL_OK. Then reply with the single word DONE and stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352050755,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/fs-write-overwrite/session.jsonl b/examples/acp-agent/tests/snapshots/fs-write-overwrite/session.jsonl
index 08ec0f1323..ab8b5965ad 100644
--- a/examples/acp-agent/tests/snapshots/fs-write-overwrite/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/fs-write-overwrite/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"e04cc262-6c89-4586-88d7-3e919240d735","createdAt":1783352092215,"cwd":"/tmp/acp-snap-cwd-hH2sGY"}
+{"type":"session","version":0,"id":"e04cc262-6c89-4586-88d7-3e919240d735","createdAt":1783352092215,"cwd":"/tmp/acp-snap-cwd-hH2sGY","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352092220,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352092221,"data":{"content":[{"type":"text","text":"First use the read tool to read data.txt in the current directory. Then use the write tool (NOT bash) to replace its entire contents with exactly the single line: replaced. Then reply with exactly the single word DONE."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352092223,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/fs-write/session.jsonl b/examples/acp-agent/tests/snapshots/fs-write/session.jsonl
index 59ba868817..04fd86da0d 100644
--- a/examples/acp-agent/tests/snapshots/fs-write/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/fs-write/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"fdcab4d0-e5e4-4a06-9195-be8f7049d67e","createdAt":1783352078749,"cwd":"/tmp/acp-snap-cwd-sNvn5N"}
+{"type":"session","version":0,"id":"fdcab4d0-e5e4-4a06-9195-be8f7049d67e","createdAt":1783352078749,"cwd":"/tmp/acp-snap-cwd-sNvn5N","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352078754,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352078754,"data":{"content":[{"type":"text","text":"Use the write tool (NOT bash) to create a file named notes.txt in the current directory containing exactly the single line: hello world. Then reply with exactly the single word DONE."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352078756,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/handshake/session.jsonl b/examples/acp-agent/tests/snapshots/handshake/session.jsonl
index a6f73319bc..63f2775383 100644
--- a/examples/acp-agent/tests/snapshots/handshake/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/handshake/session.jsonl
@@ -1 +1 @@
-{"type":"session","version":0,"id":"00000000-0000-0000-0000-000000000000","createdAt":0}
+{"type":"session","version":0,"id":"00000000-0000-0000-0000-000000000000","createdAt":0,"delegationDepth":0}
diff --git a/examples/acp-agent/tests/snapshots/hook-cc-posttool-block/session.jsonl b/examples/acp-agent/tests/snapshots/hook-cc-posttool-block/session.jsonl
index be1d70a853..c362de7a26 100644
--- a/examples/acp-agent/tests/snapshots/hook-cc-posttool-block/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/hook-cc-posttool-block/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"669e8682-49fc-4dff-9bc7-6280e283cbe4","createdAt":1783962504097,"cwd":"/var/folders/2c/psb0_fmx7hbgz558xjt_f0l00000gn/T/acp-snap-cwd-WxJGUY"}
+{"type":"session","version":0,"id":"669e8682-49fc-4dff-9bc7-6280e283cbe4","createdAt":1783962504097,"cwd":"/var/folders/2c/psb0_fmx7hbgz558xjt_f0l00000gn/T/acp-snap-cwd-WxJGUY","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783962504115,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783962504117,"data":{"content":[{"type":"text","text":"Call the bash tool to run exactly: echo HELLO. If the first tool result is rejected, retry that command once. Quote the final tool result verbatim and stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783962504152,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/hook-cc-posttool-context/session.jsonl b/examples/acp-agent/tests/snapshots/hook-cc-posttool-context/session.jsonl
index 2e167db28c..66d2a6b427 100644
--- a/examples/acp-agent/tests/snapshots/hook-cc-posttool-context/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/hook-cc-posttool-context/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"0a862642-6652-4916-b88d-b058954ab0c6","createdAt":1783352196657,"cwd":"/tmp/acp-snap-cwd-LEetSL"}
+{"type":"session","version":0,"id":"0a862642-6652-4916-b88d-b058954ab0c6","createdAt":1783352196657,"cwd":"/tmp/acp-snap-cwd-LEetSL","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352196662,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352196662,"data":{"content":[{"type":"text","text":"Use the bash tool to run exactly: echo HELLO. Report the tool result you got back verbatim, then stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352196664,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/hook-cc-pretool-ask/session.jsonl b/examples/acp-agent/tests/snapshots/hook-cc-pretool-ask/session.jsonl
index a1f46a781b..247e13a075 100644
--- a/examples/acp-agent/tests/snapshots/hook-cc-pretool-ask/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/hook-cc-pretool-ask/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"f688431c-01a8-4326-a5c5-1b5f0fd08483","createdAt":1783352171511,"cwd":"/tmp/acp-snap-cwd-iKVciS"}
+{"type":"session","version":0,"id":"f688431c-01a8-4326-a5c5-1b5f0fd08483","createdAt":1783352171511,"cwd":"/tmp/acp-snap-cwd-iKVciS","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352171519,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352171520,"data":{"content":[{"type":"text","text":"Use the bash tool to run exactly: echo HELLO. Report the tool result you got back verbatim, then stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352171527,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/hook-cc-pretool-deny/session.jsonl b/examples/acp-agent/tests/snapshots/hook-cc-pretool-deny/session.jsonl
index 9633075e5b..4193c7fe80 100644
--- a/examples/acp-agent/tests/snapshots/hook-cc-pretool-deny/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/hook-cc-pretool-deny/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"ff1c1e99-3bd4-4ef8-a954-80d607d628ba","createdAt":1783352165190,"cwd":"/tmp/acp-snap-cwd-wDnkVo"}
+{"type":"session","version":0,"id":"ff1c1e99-3bd4-4ef8-a954-80d607d628ba","createdAt":1783352165190,"cwd":"/tmp/acp-snap-cwd-wDnkVo","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352165195,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352165196,"data":{"content":[{"type":"text","text":"Use the bash tool to run exactly: echo HELLO. Report the tool result you got back verbatim, then stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352165198,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/hook-cc-promptsubmit-block/session.jsonl b/examples/acp-agent/tests/snapshots/hook-cc-promptsubmit-block/session.jsonl
index b5f81fdaea..dd6745b770 100644
--- a/examples/acp-agent/tests/snapshots/hook-cc-promptsubmit-block/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/hook-cc-promptsubmit-block/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}"}
+{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":0,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"hook/invoked","seq":1,"time":0,"data":{"turn":1,"point":"UserPromptSubmit","dialect":"claude","handlerId":"claude:UserPromptSubmit:1"}}
 {"type":"hook/result","seq":2,"time":0,"data":{"turn":1,"point":"UserPromptSubmit","handlerId":"claude:UserPromptSubmit:1","decision":"block","exitCode":2,"stderrSummary":"blocked by policy hook","durationMs":0}}
diff --git a/examples/acp-agent/tests/snapshots/hook-cc-promptsubmit-context/session.jsonl b/examples/acp-agent/tests/snapshots/hook-cc-promptsubmit-context/session.jsonl
index 886761da18..d2a0806829 100644
--- a/examples/acp-agent/tests/snapshots/hook-cc-promptsubmit-context/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/hook-cc-promptsubmit-context/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"d03c3a83-1238-4e2e-ad9a-b86a61840a40","createdAt":1783352160541,"cwd":"/tmp/acp-snap-cwd-QUDqlk"}
+{"type":"session","version":0,"id":"d03c3a83-1238-4e2e-ad9a-b86a61840a40","createdAt":1783352160541,"cwd":"/tmp/acp-snap-cwd-QUDqlk","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352160545,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"hook/invoked","seq":1,"time":1783352160546,"data":{"turn":1,"point":"UserPromptSubmit","dialect":"claude","handlerId":"claude:UserPromptSubmit:1"}}
 {"type":"hook/result","seq":2,"time":1783352160564,"data":{"turn":1,"point":"UserPromptSubmit","handlerId":"claude:UserPromptSubmit:1","decision":"pass","exitCode":0,"durationMs":17.45639600000004}}
diff --git a/examples/acp-agent/tests/snapshots/hook-cc-stop-continue/session.jsonl b/examples/acp-agent/tests/snapshots/hook-cc-stop-continue/session.jsonl
index baa6a92e9a..c03ee5bd5d 100644
--- a/examples/acp-agent/tests/snapshots/hook-cc-stop-continue/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/hook-cc-stop-continue/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"eda79fbc-8a1b-4226-b74a-f5f297484747","createdAt":1784522140642,"cwd":"/var/folders/4j/54c8wb496zxfrs1ny_21jbb00000gn/T/acp-snap-cwd-r6rWZp"}
+{"type":"session","version":0,"id":"eda79fbc-8a1b-4226-b74a-f5f297484747","createdAt":1784522140642,"cwd":"/var/folders/4j/54c8wb496zxfrs1ny_21jbb00000gn/T/acp-snap-cwd-r6rWZp","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1784522140646,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1784522140647,"data":{"content":[{"type":"text","text":"Reply with the single word FIRST and stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1784522140648,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/hook-codex-posttool-block/session.jsonl b/examples/acp-agent/tests/snapshots/hook-codex-posttool-block/session.jsonl
index 6d08c3ee7d..dc68891c14 100644
--- a/examples/acp-agent/tests/snapshots/hook-codex-posttool-block/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/hook-codex-posttool-block/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"01aa6a36-e9c2-42ba-934b-30bec80a1658","createdAt":1783986962232,"cwd":"/var/folders/2c/psb0_fmx7hbgz558xjt_f0l00000gn/T/acp-snap-cwd-x67BsP"}
+{"type":"session","version":0,"id":"01aa6a36-e9c2-42ba-934b-30bec80a1658","createdAt":1783986962232,"cwd":"/var/folders/2c/psb0_fmx7hbgz558xjt_f0l00000gn/T/acp-snap-cwd-x67BsP","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783986962235,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783986962235,"data":{"content":[{"type":"text","text":"Call the bash tool exactly once to run: echo HELLO. Whatever tool result comes back, quote it verbatim and stop without calling another tool."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783986962240,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/hook-codex-posttool-context/session.jsonl b/examples/acp-agent/tests/snapshots/hook-codex-posttool-context/session.jsonl
index d60858ee0a..b7e97b3a65 100644
--- a/examples/acp-agent/tests/snapshots/hook-codex-posttool-context/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/hook-codex-posttool-context/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"39d8aabe-6457-4a0e-83b7-ee33125a3666","createdAt":1783352228436,"cwd":"/tmp/acp-snap-cwd-VGFtPi"}
+{"type":"session","version":0,"id":"39d8aabe-6457-4a0e-83b7-ee33125a3666","createdAt":1783352228436,"cwd":"/tmp/acp-snap-cwd-VGFtPi","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352228441,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352228442,"data":{"content":[{"type":"text","text":"Use the bash tool to run exactly: echo HELLO. Report the tool result you got back verbatim, then stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352228443,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/hook-codex-pretool-block/session.jsonl b/examples/acp-agent/tests/snapshots/hook-codex-pretool-block/session.jsonl
index 812998aad5..c2675ae3af 100644
--- a/examples/acp-agent/tests/snapshots/hook-codex-pretool-block/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/hook-codex-pretool-block/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"57a74aed-99fc-43bc-a875-6dddebf64d69","createdAt":1783352214599,"cwd":"/tmp/acp-snap-cwd-7Hbu0m"}
+{"type":"session","version":0,"id":"57a74aed-99fc-43bc-a875-6dddebf64d69","createdAt":1783352214599,"cwd":"/tmp/acp-snap-cwd-7Hbu0m","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352214604,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352214605,"data":{"content":[{"type":"text","text":"Use the bash tool to run exactly: echo HELLO. Report the tool result you got back verbatim, then stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352214607,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/hook-codex-promptsubmit-block/session.jsonl b/examples/acp-agent/tests/snapshots/hook-codex-promptsubmit-block/session.jsonl
index bc9144f980..126a761309 100644
--- a/examples/acp-agent/tests/snapshots/hook-codex-promptsubmit-block/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/hook-codex-promptsubmit-block/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}"}
+{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":0,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"hook/invoked","seq":1,"time":0,"data":{"turn":1,"point":"UserPromptSubmit","dialect":"codex","handlerId":"codex:UserPromptSubmit:1"}}
 {"type":"hook/result","seq":2,"time":0,"data":{"turn":1,"point":"UserPromptSubmit","handlerId":"codex:UserPromptSubmit:1","decision":"block","exitCode":2,"stderrSummary":"blocked by codex policy hook","durationMs":0}}
diff --git a/examples/acp-agent/tests/snapshots/hook-codex-promptsubmit-context/session.jsonl b/examples/acp-agent/tests/snapshots/hook-codex-promptsubmit-context/session.jsonl
index 1c710ff8e1..ad7538cba9 100644
--- a/examples/acp-agent/tests/snapshots/hook-codex-promptsubmit-context/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/hook-codex-promptsubmit-context/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"0bebc0f4-a089-4fde-9b6e-db9532cfd4de","createdAt":1783352209682,"cwd":"/tmp/acp-snap-cwd-aopaZV"}
+{"type":"session","version":0,"id":"0bebc0f4-a089-4fde-9b6e-db9532cfd4de","createdAt":1783352209682,"cwd":"/tmp/acp-snap-cwd-aopaZV","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352209686,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"hook/invoked","seq":1,"time":1783352209687,"data":{"turn":1,"point":"UserPromptSubmit","dialect":"codex","handlerId":"codex:UserPromptSubmit:1"}}
 {"type":"hook/result","seq":2,"time":1783352209706,"data":{"turn":1,"point":"UserPromptSubmit","handlerId":"codex:UserPromptSubmit:1","decision":"pass","exitCode":0,"durationMs":19.49695100000008}}
diff --git a/examples/acp-agent/tests/snapshots/hook-codex-stop-continue/session.jsonl b/examples/acp-agent/tests/snapshots/hook-codex-stop-continue/session.jsonl
index cee758076c..5cf14d9b49 100644
--- a/examples/acp-agent/tests/snapshots/hook-codex-stop-continue/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/hook-codex-stop-continue/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"eb17be12-ca8c-46c8-b500-0977e8400208","createdAt":1784522152392,"cwd":"/var/folders/4j/54c8wb496zxfrs1ny_21jbb00000gn/T/acp-snap-cwd-ESgqLu"}
+{"type":"session","version":0,"id":"eb17be12-ca8c-46c8-b500-0977e8400208","createdAt":1784522152392,"cwd":"/var/folders/4j/54c8wb496zxfrs1ny_21jbb00000gn/T/acp-snap-cwd-ESgqLu","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1784522152397,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1784522152397,"data":{"content":[{"type":"text","text":"Reply with the single word FIRST and stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1784522152399,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/model-switching/session.jsonl b/examples/acp-agent/tests/snapshots/model-switching/session.jsonl
index 1f04eca07d..ddc592bbb6 100644
--- a/examples/acp-agent/tests/snapshots/model-switching/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/model-switching/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"622d16ce-0a94-476b-97a4-26dad50b1fbf","createdAt":1784086275585,"cwd":"/var/folders/_g/59jgff8x2gqd39f5vy1wnbfc0000gn/T/acp-snap-cwd-Cwf7Bh"}
+{"type":"session","version":0,"id":"622d16ce-0a94-476b-97a4-26dad50b1fbf","createdAt":1784086275585,"cwd":"/var/folders/_g/59jgff8x2gqd39f5vy1wnbfc0000gn/T/acp-snap-cwd-Cwf7Bh","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1784086275588,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1784086275588,"data":{"content":[{"type":"text","text":"Without using tools, reply with exactly FLASH and stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1784086275590,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/multi-turn/session.jsonl b/examples/acp-agent/tests/snapshots/multi-turn/session.jsonl
index cd32072eaa..83ccf18a3f 100644
--- a/examples/acp-agent/tests/snapshots/multi-turn/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/multi-turn/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"228b7b82-84ed-49b7-a567-981c03b28c77","createdAt":1783352113760,"cwd":"/tmp/acp-snap-cwd-aN2GRR"}
+{"type":"session","version":0,"id":"228b7b82-84ed-49b7-a567-981c03b28c77","createdAt":1783352113760,"cwd":"/tmp/acp-snap-cwd-aN2GRR","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352113765,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352113765,"data":{"content":[{"type":"text","text":"Reply with exactly the word: ONE. No tools."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352113767,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/parallel-tool-calls/session.jsonl b/examples/acp-agent/tests/snapshots/parallel-tool-calls/session.jsonl
index 81503dc4cf..e83f0cd59c 100644
--- a/examples/acp-agent/tests/snapshots/parallel-tool-calls/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/parallel-tool-calls/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}"}
+{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":0,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":0,"data":{"content":[{"type":"text","text":"Use the read tool twice in the same assistant message: read a.txt and b.txt. Then reply DONE."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":0,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/permission-switching/session.jsonl b/examples/acp-agent/tests/snapshots/permission-switching/session.jsonl
index 43fc43d979..ff44da7e1d 100644
--- a/examples/acp-agent/tests/snapshots/permission-switching/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/permission-switching/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"df041acb-2f14-4d5f-b6e2-2fb6b9eb6427","createdAt":1783860666204,"cwd":"/var/folders/2g/b32ct0qn1d728l_v6tdkjytr0000gn/T/acp-snap-cwd-4oJKT4"}
+{"type":"session","version":0,"id":"df041acb-2f14-4d5f-b6e2-2fb6b9eb6427","createdAt":1783860666204,"cwd":"/var/folders/2g/b32ct0qn1d728l_v6tdkjytr0000gn/T/acp-snap-cwd-4oJKT4","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783860666206,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"permission/preset","seq":1,"time":1783962244578,"data":{"preset":"workspace-write"}}
 {"type":"sandbox/mode","seq":2,"time":1784518115721,"data":{"mode":"workspace-write"}}
diff --git a/examples/acp-agent/tests/snapshots/reject-extra-dirs/session.jsonl b/examples/acp-agent/tests/snapshots/reject-extra-dirs/session.jsonl
index a6f73319bc..63f2775383 100644
--- a/examples/acp-agent/tests/snapshots/reject-extra-dirs/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/reject-extra-dirs/session.jsonl
@@ -1 +1 @@
-{"type":"session","version":0,"id":"00000000-0000-0000-0000-000000000000","createdAt":0}
+{"type":"session","version":0,"id":"00000000-0000-0000-0000-000000000000","createdAt":0,"delegationDepth":0}
diff --git a/examples/acp-agent/tests/snapshots/repeat-tool-guard/session.jsonl b/examples/acp-agent/tests/snapshots/repeat-tool-guard/session.jsonl
index 20d18973d9..c77e0ef38d 100644
--- a/examples/acp-agent/tests/snapshots/repeat-tool-guard/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/repeat-tool-guard/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}"}
+{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":0,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":0,"data":{"content":[{"type":"text","text":"Write the todo list 'watch the kettle boil' five times in a row without changing it, then reply DONE."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":0,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/skill-load/session.jsonl b/examples/acp-agent/tests/snapshots/skill-load/session.jsonl
index 0fe1a5152c..1a9704954a 100644
--- a/examples/acp-agent/tests/snapshots/skill-load/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/skill-load/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"9eb4181f-2d05-49d3-98fc-3711fe2f5664","createdAt":1783654655599,"cwd":"/var/folders/_g/59jgff8x2gqd39f5vy1wnbfc0000gn/T/acp-snap-cwd-DhYwNW"}
+{"type":"session","version":0,"id":"9eb4181f-2d05-49d3-98fc-3711fe2f5664","createdAt":1783654655599,"cwd":"/var/folders/_g/59jgff8x2gqd39f5vy1wnbfc0000gn/T/acp-snap-cwd-DhYwNW","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783654655602,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783654655603,"data":{"content":[{"type":"text","text":"Load the snapshot-skill skill with the skill tool, then reply DONE."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783654655608,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/input.json b/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/input.json
new file mode 100644
index 0000000000..414a33affe
--- /dev/null
+++ b/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/input.json
@@ -0,0 +1,7 @@
+{
+  "steps": [
+    { "op": "initialize" },
+    { "op": "newSession" },
+    { "op": "prompt", "text": "Delegate through two child generations. The depth-two child must attempt one more subagent call and report the rejection." }
+  ]
+}
diff --git a/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/replay.override.json b/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/replay.override.json
new file mode 100644
index 0000000000..ea012cfb63
--- /dev/null
+++ b/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/replay.override.json
@@ -0,0 +1,22 @@
+[
+  {
+    "kind": "chunks",
+    "chunks": [
+      { "type": "block-start", "index": 0, "blockType": "tool-call" },
+      { "type": "tool-call-delta", "index": 0, "id": "call_root_child", "name": "subagent", "argumentsDelta": "{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\"}" },
+      { "type": "block-end", "index": 0, "block": { "type": "tool-call", "id": "call_root_child", "name": "subagent", "arguments": "{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\"}" } },
+      { "type": "usage", "usage": { "inputTokens": 10, "outputTokens": 5 } },
+      { "type": "finish", "reason": { "kind": "tool-calls" } }
+    ]
+  },
+  {
+    "kind": "chunks",
+    "chunks": [
+      { "type": "block-start", "index": 0, "blockType": "text" },
+      { "type": "text-delta", "index": 0, "text": "ROOT_DONE" },
+      { "type": "block-end", "index": 0, "block": { "type": "text", "text": "ROOT_DONE" } },
+      { "type": "usage", "usage": { "inputTokens": 10, "outputTokens": 2 } },
+      { "type": "finish", "reason": { "kind": "stop" } }
+    ]
+  }
+]
diff --git a/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/session.1.jsonl b/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/session.1.jsonl
new file mode 100644
index 0000000000..b7017c51f3
--- /dev/null
+++ b/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/session.1.jsonl
@@ -0,0 +1,23 @@
+{"type":"session","version":0,"id":"22222222-2222-4222-8222-222222222222","createdAt":1001,"cwd":"/tmp/subagent-depth-two","parentSession":"11111111-1111-4111-8111-111111111111","delegationDepth":1}
+{"type":"turn/start","seq":0,"time":1784540790312,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
+{"type":"user/message","seq":1,"time":1784540790312,"data":{"content":[{"type":"text","text":"Call subagent once. Ask that child to attempt one further subagent call, then report the result."}],"source":{"kind":"user"}},"surfaceOp":"append"}
+{"type":"step/start","seq":2,"time":1784540790318,"data":{"turn":1,"step":1}}
+{"type":"request/header","seq":3,"time":1784540790318,"data":{"header":{"config":{"provider":"deepseek","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
+{"type":"assistant/chunk","seq":4,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}}}
+{"type":"assistant/chunk","seq":5,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"call_depth_one_child","name":"subagent","argumentsDelta":"{\"description\":\"Start depth two\",\"prompt\":\"Attempt one subagent call beyond the configured cap, then report the rejection.\"}"}}}
+{"type":"assistant/chunk","seq":6,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_depth_one_child","name":"subagent","arguments":"{\"description\":\"Start depth two\",\"prompt\":\"Attempt one subagent call beyond the configured cap, then report the rejection.\"}"}}}}
+{"type":"assistant/chunk","seq":7,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":10,"outputTokens":5}}}}
+{"type":"assistant/chunk","seq":8,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
+{"type":"assistant/message","seq":9,"time":1784540790318,"data":{"turn":1,"step":1,"content":[{"type":"tool-call","id":"call_depth_one_child","name":"subagent","arguments":"{\"description\":\"Start depth two\",\"prompt\":\"Attempt one subagent call beyond the configured cap, then report the rejection.\"}"}],"provenance":{"provider":"deepseek","model":"deepseek-v4-flash"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[4,5,6,7,8],"surfaceOp":"append"}
+{"type":"tool/call","seq":10,"time":1784540790319,"data":{"turn":1,"step":1,"callId":"call_depth_one_child","name":"subagent","arguments":"{\"description\":\"Start depth two\",\"prompt\":\"Attempt one subagent call beyond the configured cap, then report the rejection.\"}"}}
+{"type":"tool/result","seq":11,"time":1784540790362,"data":{"turn":1,"step":1,"callId":"call_depth_one_child","content":[{"type":"text","text":"DEPTH_REJECTED"}],"isError":false},"sourceEventSeqs":[10],"surfaceOp":"append"}
+{"type":"step/end","seq":12,"time":1784540790363,"data":{"turn":1,"step":1}}
+{"type":"step/start","seq":13,"time":1784540790364,"data":{"turn":1,"step":2}}
+{"type":"assistant/chunk","seq":14,"time":1784540790365,"data":{"turn":1,"step":2,"chunk":{"type":"block-start","index":0,"blockType":"text"}}}
+{"type":"assistant/chunk","seq":15,"time":1784540790365,"data":{"turn":1,"step":2,"chunk":{"type":"text-delta","index":0,"text":"DEPTH_ONE_DONE"}}}
+{"type":"assistant/chunk","seq":16,"time":1784540790365,"data":{"turn":1,"step":2,"chunk":{"type":"block-end","index":0,"block":{"type":"text","text":"DEPTH_ONE_DONE"}}}}
+{"type":"assistant/chunk","seq":17,"time":1784540790365,"data":{"turn":1,"step":2,"chunk":{"type":"usage","usage":{"inputTokens":10,"outputTokens":2}}}}
+{"type":"assistant/chunk","seq":18,"time":1784540790365,"data":{"turn":1,"step":2,"chunk":{"type":"finish","reason":{"kind":"stop"}}}}
+{"type":"assistant/message","seq":19,"time":1784540790365,"data":{"turn":1,"step":2,"content":[{"type":"text","text":"DEPTH_ONE_DONE"}],"provenance":{"provider":"deepseek","model":"deepseek-v4-flash"},"usage":{"inputTokens":10,"outputTokens":2}},"sourceEventSeqs":[14,15,16,17,18],"surfaceOp":"append"}
+{"type":"step/end","seq":20,"time":1784540790365,"data":{"turn":1,"step":2}}
+{"type":"turn/end","seq":21,"time":1784540790365,"data":{"turn":1,"reason":{"kind":"completed"}}}
diff --git a/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/session.2.jsonl b/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/session.2.jsonl
new file mode 100644
index 0000000000..7b36136970
--- /dev/null
+++ b/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/session.2.jsonl
@@ -0,0 +1,23 @@
+{"type":"session","version":0,"id":"33333333-3333-4333-8333-333333333333","createdAt":1002,"cwd":"/tmp/subagent-depth-two","parentSession":"22222222-2222-4222-8222-222222222222","delegationDepth":2}
+{"type":"turn/start","seq":0,"time":1784540790319,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
+{"type":"user/message","seq":1,"time":1784540790319,"data":{"content":[{"type":"text","text":"Attempt one subagent call beyond the configured cap, then report the rejection."}],"source":{"kind":"user"}},"surfaceOp":"append"}
+{"type":"step/start","seq":2,"time":1784540790334,"data":{"turn":1,"step":1}}
+{"type":"request/header","seq":3,"time":1784540790334,"data":{"header":{"config":{"provider":"deepseek","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
+{"type":"assistant/chunk","seq":4,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}}}
+{"type":"assistant/chunk","seq":5,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"call_depth_three_rejected","name":"subagent","argumentsDelta":"{\"description\":\"Exceed depth cap\",\"prompt\":\"This child must never start.\"}"}}}
+{"type":"assistant/chunk","seq":6,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_depth_three_rejected","name":"subagent","arguments":"{\"description\":\"Exceed depth cap\",\"prompt\":\"This child must never start.\"}"}}}}
+{"type":"assistant/chunk","seq":7,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":10,"outputTokens":5}}}}
+{"type":"assistant/chunk","seq":8,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
+{"type":"assistant/message","seq":9,"time":1784540790335,"data":{"turn":1,"step":1,"content":[{"type":"tool-call","id":"call_depth_three_rejected","name":"subagent","arguments":"{\"description\":\"Exceed depth cap\",\"prompt\":\"This child must never start.\"}"}],"provenance":{"provider":"deepseek","model":"deepseek-v4-flash"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[4,5,6,7,8],"surfaceOp":"append"}
+{"type":"tool/call","seq":10,"time":1784540790335,"data":{"turn":1,"step":1,"callId":"call_depth_three_rejected","name":"subagent","arguments":"{\"description\":\"Exceed depth cap\",\"prompt\":\"This child must never start.\"}"}}
+{"type":"tool/result","seq":11,"time":1784540790337,"data":{"turn":1,"step":1,"callId":"call_depth_three_rejected","content":[{"type":"text","text":"Error: subagent depth 3 exceeds maxDepth 2"}],"isError":true},"sourceEventSeqs":[10],"surfaceOp":"append"}
+{"type":"step/end","seq":12,"time":1784540790338,"data":{"turn":1,"step":1}}
+{"type":"step/start","seq":13,"time":1784540790338,"data":{"turn":1,"step":2}}
+{"type":"assistant/chunk","seq":14,"time":1784540790339,"data":{"turn":1,"step":2,"chunk":{"type":"block-start","index":0,"blockType":"text"}}}
+{"type":"assistant/chunk","seq":15,"time":1784540790339,"data":{"turn":1,"step":2,"chunk":{"type":"text-delta","index":0,"text":"DEPTH_REJECTED"}}}
+{"type":"assistant/chunk","seq":16,"time":1784540790339,"data":{"turn":1,"step":2,"chunk":{"type":"block-end","index":0,"block":{"type":"text","text":"DEPTH_REJECTED"}}}}
+{"type":"assistant/chunk","seq":17,"time":1784540790339,"data":{"turn":1,"step":2,"chunk":{"type":"usage","usage":{"inputTokens":10,"outputTokens":2}}}}
+{"type":"assistant/chunk","seq":18,"time":1784540790339,"data":{"turn":1,"step":2,"chunk":{"type":"finish","reason":{"kind":"stop"}}}}
+{"type":"assistant/message","seq":19,"time":1784540790339,"data":{"turn":1,"step":2,"content":[{"type":"text","text":"DEPTH_REJECTED"}],"provenance":{"provider":"deepseek","model":"deepseek-v4-flash"},"usage":{"inputTokens":10,"outputTokens":2}},"sourceEventSeqs":[14,15,16,17,18],"surfaceOp":"append"}
+{"type":"step/end","seq":20,"time":1784540790339,"data":{"turn":1,"step":2}}
+{"type":"turn/end","seq":21,"time":1784540790339,"data":{"turn":1,"reason":{"kind":"completed"}}}
diff --git a/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/session.jsonl b/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/session.jsonl
new file mode 100644
index 0000000000..b9bdc1baea
--- /dev/null
+++ b/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/session.jsonl
@@ -0,0 +1,23 @@
+{"type":"session","version":0,"id":"11111111-1111-4111-8111-111111111111","createdAt":1000,"cwd":"/tmp/subagent-depth-two","delegationDepth":0}
+{"type":"turn/start","seq":0,"time":1784540790290,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
+{"type":"user/message","seq":1,"time":1784540790291,"data":{"content":[{"type":"text","text":"Delegate through two child generations. The depth-two child must attempt one more subagent call and report the rejection."}],"source":{"kind":"user"}},"surfaceOp":"append"}
+{"type":"step/start","seq":2,"time":1784540790308,"data":{"turn":1,"step":1}}
+{"type":"request/header","seq":3,"time":1784540790308,"data":{"header":{"config":{"provider":"deepseek","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
+{"type":"assistant/chunk","seq":4,"time":1784540790309,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}}}
+{"type":"assistant/chunk","seq":5,"time":1784540790309,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"call_root_child","name":"subagent","argumentsDelta":"{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\"}"}}}
+{"type":"assistant/chunk","seq":6,"time":1784540790309,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_root_child","name":"subagent","arguments":"{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\"}"}}}}
+{"type":"assistant/chunk","seq":7,"time":1784540790309,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":10,"outputTokens":5}}}}
+{"type":"assistant/chunk","seq":8,"time":1784540790309,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
+{"type":"assistant/message","seq":9,"time":1784540790310,"data":{"turn":1,"step":1,"content":[{"type":"tool-call","id":"call_root_child","name":"subagent","arguments":"{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\"}"}],"provenance":{"provider":"deepseek","model":"deepseek-v4-flash"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[4,5,6,7,8],"surfaceOp":"append"}
+{"type":"tool/call","seq":10,"time":1784540790310,"data":{"turn":1,"step":1,"callId":"call_root_child","name":"subagent","arguments":"{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\"}"}}
+{"type":"tool/result","seq":11,"time":1784540790381,"data":{"turn":1,"step":1,"callId":"call_root_child","content":[{"type":"text","text":"DEPTH_ONE_DONE"}],"isError":false},"sourceEventSeqs":[10],"surfaceOp":"append"}
+{"type":"step/end","seq":12,"time":1784540790382,"data":{"turn":1,"step":1}}
+{"type":"step/start","seq":13,"time":1784540790382,"data":{"turn":1,"step":2}}
+{"type":"assistant/chunk","seq":14,"time":1784540790383,"data":{"turn":1,"step":2,"chunk":{"type":"block-start","index":0,"blockType":"text"}}}
+{"type":"assistant/chunk","seq":15,"time":1784540790383,"data":{"turn":1,"step":2,"chunk":{"type":"text-delta","index":0,"text":"ROOT_DONE"}}}
+{"type":"assistant/chunk","seq":16,"time":1784540790383,"data":{"turn":1,"step":2,"chunk":{"type":"block-end","index":0,"block":{"type":"text","text":"ROOT_DONE"}}}}
+{"type":"assistant/chunk","seq":17,"time":1784540790383,"data":{"turn":1,"step":2,"chunk":{"type":"usage","usage":{"inputTokens":10,"outputTokens":2}}}}
+{"type":"assistant/chunk","seq":18,"time":1784540790383,"data":{"turn":1,"step":2,"chunk":{"type":"finish","reason":{"kind":"stop"}}}}
+{"type":"assistant/message","seq":19,"time":1784540790383,"data":{"turn":1,"step":2,"content":[{"type":"text","text":"ROOT_DONE"}],"provenance":{"provider":"deepseek","model":"deepseek-v4-flash"},"usage":{"inputTokens":10,"outputTokens":2}},"sourceEventSeqs":[14,15,16,17,18],"surfaceOp":"append"}
+{"type":"step/end","seq":20,"time":1784540790383,"data":{"turn":1,"step":2}}
+{"type":"turn/end","seq":21,"time":1784540790383,"data":{"turn":1,"reason":{"kind":"completed"}}}
diff --git a/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/stdout.expected.jsonl b/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/stdout.expected.jsonl
new file mode 100644
index 0000000000..7f629a2d71
--- /dev/null
+++ b/examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/stdout.expected.jsonl
@@ -0,0 +1,6 @@
+{"jsonrpc":"2.0","id":1,"result":{"protocolVersion":1,"agentInfo":{"name":"deepseek-harness-acp","version":"0.0.1"},"agentCapabilities":{"loadSession":true,"promptCapabilities":{"image":false,"audio":false,"embeddedContext":false}},"authMethods":[]}}
+{"jsonrpc":"2.0","id":2,"result":{"sessionId":"{{sessionId}}","configOptions":[{"id":"model","name":"Model","description":"Sets this session's provider and model.","category":"model","type":"select","currentValue":"[\"deepseek\",\"deepseek-v4-flash\"]","options":[{"value":"[\"deepseek\",\"deepseek-v4-flash\"]","name":"deepseek-v4-flash"},{"value":"[\"deepseek\",\"deepseek-v4-pro\"]","name":"deepseek-v4-pro"}]},{"id":"permission","name":"Permissions","description":"The session permission preset: each choice bundles a sandbox mode and an approval policy.","category":"mode","type":"select","currentValue":"danger-full-access","options":[{"value":"workspace-write","name":"workspace-write","description":"Write inside the workspace and permitted temporary directories; wider retries require approval."},{"value":"danger-full-access","name":"danger-full-access","description":"Full file access without approval prompts."}]}]}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"tool_call","toolCallId":"call_root_child","title":"subagent","kind":"other","status":"in_progress","rawInput":{"description":"Start depth one","prompt":"Call subagent once. Ask that child to attempt one further subagent call, then report the result."}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"tool_call_update","toolCallId":"call_root_child","status":"completed","content":[{"type":"content","content":{"type":"text","text":"DEPTH_ONE_DONE"}}]}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":"ROOT_DONE"}}}}
+{"jsonrpc":"2.0","id":3,"result":{"stopReason":"end_turn"}}
diff --git a/examples/acp-agent/tests/snapshots/subagent-fork/session.1.jsonl b/examples/acp-agent/tests/snapshots/subagent-fork/session.1.jsonl
index 4ecb61b60f..0ec70d6f81 100644
--- a/examples/acp-agent/tests/snapshots/subagent-fork/session.1.jsonl
+++ b/examples/acp-agent/tests/snapshots/subagent-fork/session.1.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"ada8966c-9fa3-441b-8721-37ff1e795e6a","createdAt":1783352137161,"cwd":"/tmp/acp-snap-cwd-0HLtcD","parentSession":"96cf59c9-b347-48b9-b234-a5200913ad05","seedLength":37}
+{"type":"session","version":0,"id":"ada8966c-9fa3-441b-8721-37ff1e795e6a","createdAt":1783352137161,"cwd":"/tmp/acp-snap-cwd-0HLtcD","parentSession":"96cf59c9-b347-48b9-b234-a5200913ad05","seedLength":37,"delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783352134837,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352134838,"data":{"content":[{"type":"text","text":"Remember this fact for later: the project codeword is MARMALADE. Reply with the single word OK and stop. Do not use any tools."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352134840,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/subagent-fork/session.jsonl b/examples/acp-agent/tests/snapshots/subagent-fork/session.jsonl
index 64da6e60e5..60c1e5cc10 100644
--- a/examples/acp-agent/tests/snapshots/subagent-fork/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/subagent-fork/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"96cf59c9-b347-48b9-b234-a5200913ad05","createdAt":1783352134832,"cwd":"/tmp/acp-snap-cwd-0HLtcD"}
+{"type":"session","version":0,"id":"96cf59c9-b347-48b9-b234-a5200913ad05","createdAt":1783352134832,"cwd":"/tmp/acp-snap-cwd-0HLtcD","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352134837,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352134838,"data":{"content":[{"type":"text","text":"Remember this fact for later: the project codeword is MARMALADE. Reply with the single word OK and stop. Do not use any tools."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352134840,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/subagent-mixed/session.1.jsonl b/examples/acp-agent/tests/snapshots/subagent-mixed/session.1.jsonl
index c99a5681e2..4c8d25ad82 100644
--- a/examples/acp-agent/tests/snapshots/subagent-mixed/session.1.jsonl
+++ b/examples/acp-agent/tests/snapshots/subagent-mixed/session.1.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"e4aafa18-b9e3-48d0-8aae-6c9b25dcae80","createdAt":1783352145223,"cwd":"/tmp/acp-snap-cwd-i43JSF","parentSession":"959ffdf5-03e2-465e-9482-009b704632dc"}
+{"type":"session","version":0,"id":"e4aafa18-b9e3-48d0-8aae-6c9b25dcae80","createdAt":1783352145223,"cwd":"/tmp/acp-snap-cwd-i43JSF","parentSession":"959ffdf5-03e2-465e-9482-009b704632dc","delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783352145224,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352145224,"data":{"content":[{"type":"text","text":"Reply with exactly the word ALPHA and nothing else."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352145224,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/subagent-mixed/session.2.jsonl b/examples/acp-agent/tests/snapshots/subagent-mixed/session.2.jsonl
index adfcb6f60e..4bc55d2910 100644
--- a/examples/acp-agent/tests/snapshots/subagent-mixed/session.2.jsonl
+++ b/examples/acp-agent/tests/snapshots/subagent-mixed/session.2.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"02b3a8dd-1d5e-4866-825f-5fbf5000a632","createdAt":1783352147504,"cwd":"/tmp/acp-snap-cwd-i43JSF","parentSession":"959ffdf5-03e2-465e-9482-009b704632dc","seedLength":31}
+{"type":"session","version":0,"id":"02b3a8dd-1d5e-4866-825f-5fbf5000a632","createdAt":1783352147504,"cwd":"/tmp/acp-snap-cwd-i43JSF","parentSession":"959ffdf5-03e2-465e-9482-009b704632dc","seedLength":31,"delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783352142834,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352142834,"data":{"content":[{"type":"text","text":"Remember this fact for later: the project codeword is SAFFRON. Reply with the single word OK and stop. Do not use any tools."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352142835,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/subagent-mixed/session.jsonl b/examples/acp-agent/tests/snapshots/subagent-mixed/session.jsonl
index 1ea4f541e1..b977a17e16 100644
--- a/examples/acp-agent/tests/snapshots/subagent-mixed/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/subagent-mixed/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"959ffdf5-03e2-465e-9482-009b704632dc","createdAt":1783352142830,"cwd":"/tmp/acp-snap-cwd-i43JSF"}
+{"type":"session","version":0,"id":"959ffdf5-03e2-465e-9482-009b704632dc","createdAt":1783352142830,"cwd":"/tmp/acp-snap-cwd-i43JSF","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352142834,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352142834,"data":{"content":[{"type":"text","text":"Remember this fact for later: the project codeword is SAFFRON. Reply with the single word OK and stop. Do not use any tools."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352142835,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/subagent-multi/session.1.jsonl b/examples/acp-agent/tests/snapshots/subagent-multi/session.1.jsonl
index 86c481c5ff..53b59caa4b 100644
--- a/examples/acp-agent/tests/snapshots/subagent-multi/session.1.jsonl
+++ b/examples/acp-agent/tests/snapshots/subagent-multi/session.1.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"553f8e92-aac1-4df3-8657-eacbb58f9581","createdAt":1783352127669,"cwd":"/tmp/acp-snap-cwd-28z5Of","parentSession":"14dda109-5728-45ba-a002-7db9543fe50e"}
+{"type":"session","version":0,"id":"553f8e92-aac1-4df3-8657-eacbb58f9581","createdAt":1783352127669,"cwd":"/tmp/acp-snap-cwd-28z5Of","parentSession":"14dda109-5728-45ba-a002-7db9543fe50e","delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783352127670,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352127670,"data":{"content":[{"type":"text","text":"Reply with exactly the word ALPHA and nothing else."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352127671,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/subagent-multi/session.2.jsonl b/examples/acp-agent/tests/snapshots/subagent-multi/session.2.jsonl
index 483e687a14..412ae705db 100644
--- a/examples/acp-agent/tests/snapshots/subagent-multi/session.2.jsonl
+++ b/examples/acp-agent/tests/snapshots/subagent-multi/session.2.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"5f49e80c-16fc-42c7-a617-0b6bd0680aa3","createdAt":1783352129662,"cwd":"/tmp/acp-snap-cwd-28z5Of","parentSession":"14dda109-5728-45ba-a002-7db9543fe50e"}
+{"type":"session","version":0,"id":"5f49e80c-16fc-42c7-a617-0b6bd0680aa3","createdAt":1783352129662,"cwd":"/tmp/acp-snap-cwd-28z5Of","parentSession":"14dda109-5728-45ba-a002-7db9543fe50e","delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783352129662,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352129662,"data":{"content":[{"type":"text","text":"Reply with exactly the word BETA and nothing else."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352129663,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/subagent-multi/session.jsonl b/examples/acp-agent/tests/snapshots/subagent-multi/session.jsonl
index a8093fba04..b632943f89 100644
--- a/examples/acp-agent/tests/snapshots/subagent-multi/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/subagent-multi/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"14dda109-5728-45ba-a002-7db9543fe50e","createdAt":1783352126247,"cwd":"/tmp/acp-snap-cwd-28z5Of"}
+{"type":"session","version":0,"id":"14dda109-5728-45ba-a002-7db9543fe50e","createdAt":1783352126247,"cwd":"/tmp/acp-snap-cwd-28z5Of","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352126251,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352126251,"data":{"content":[{"type":"text","text":"Use the subagent tool TWICE, once at a time, to delegate two subtasks to child agents. First subtask: 'Reply with exactly the word ALPHA and nothing else.' Second subtask (after the first returns): 'Reply with exactly the word BETA and nothing else.' After both subagents return, reply with the single word PARENT_DONE and stop. Do not use the bash tool."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352126252,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/subagent-spawn/session.1.jsonl b/examples/acp-agent/tests/snapshots/subagent-spawn/session.1.jsonl
index 8dd26c4e70..3d0bf1e801 100644
--- a/examples/acp-agent/tests/snapshots/subagent-spawn/session.1.jsonl
+++ b/examples/acp-agent/tests/snapshots/subagent-spawn/session.1.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"ea339828-7885-42e1-9083-4355e6f1708d","createdAt":1783352120855,"cwd":"/tmp/acp-snap-cwd-rbeWyt","parentSession":"5138ed0d-e86e-4a7d-b75b-803307e92b17"}
+{"type":"session","version":0,"id":"ea339828-7885-42e1-9083-4355e6f1708d","createdAt":1783352120855,"cwd":"/tmp/acp-snap-cwd-rbeWyt","parentSession":"5138ed0d-e86e-4a7d-b75b-803307e92b17","delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783352120856,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352120856,"data":{"content":[{"type":"text","text":"Reply with exactly the word CHILD_OK and nothing else."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352120856,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/subagent-spawn/session.jsonl b/examples/acp-agent/tests/snapshots/subagent-spawn/session.jsonl
index 6a87cfabb5..655fb4f2a0 100644
--- a/examples/acp-agent/tests/snapshots/subagent-spawn/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/subagent-spawn/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"5138ed0d-e86e-4a7d-b75b-803307e92b17","createdAt":1783352119267,"cwd":"/tmp/acp-snap-cwd-rbeWyt"}
+{"type":"session","version":0,"id":"5138ed0d-e86e-4a7d-b75b-803307e92b17","createdAt":1783352119267,"cwd":"/tmp/acp-snap-cwd-rbeWyt","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352119273,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352119274,"data":{"content":[{"type":"text","text":"Use the subagent tool exactly once to delegate this subtask to a child agent: 'Reply with exactly the word CHILD_OK and nothing else.' After the subagent returns, reply with the single word PARENT_DONE and stop. Do not use the bash tool."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352119275,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/text-turn/session.jsonl b/examples/acp-agent/tests/snapshots/text-turn/session.jsonl
index 04ac2f9794..1f2209ca19 100644
--- a/examples/acp-agent/tests/snapshots/text-turn/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/text-turn/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"539aa64c-7f37-40ff-abd8-ed45b717be1b","createdAt":1783600629539,"cwd":"/var/folders/bn/vj1dvck95yd5jh3x4wskflxm0000gn/T/acp-snap-cwd-ka5r8w"}
+{"type":"session","version":0,"id":"539aa64c-7f37-40ff-abd8-ed45b717be1b","createdAt":1783600629539,"cwd":"/var/folders/bn/vj1dvck95yd5jh3x4wskflxm0000gn/T/acp-snap-cwd-ka5r8w","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783600629541,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783600629541,"data":{"content":[{"type":"text","text":"Reply with exactly the word: PONG. Do not use any tools."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783600629542,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/todo-plan/session.jsonl b/examples/acp-agent/tests/snapshots/todo-plan/session.jsonl
index 909afc44cd..cea8a4fa88 100644
--- a/examples/acp-agent/tests/snapshots/todo-plan/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/todo-plan/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"b0f1f758-dcf0-474e-851d-e62c11ec0a09","createdAt":1783352057652,"cwd":"/tmp/acp-snap-cwd-AYilT7"}
+{"type":"session","version":0,"id":"b0f1f758-dcf0-474e-851d-e62c11ec0a09","createdAt":1783352057652,"cwd":"/tmp/acp-snap-cwd-AYilT7","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352057655,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352057655,"data":{"content":[{"type":"text","text":"Use the todo_write tool to record a plan with exactly three todos: \"read the code\" (in_progress), \"write the fix\" (pending), \"run the tests\" (pending). Send all three in one todo_write call. Then reply with the single word DONE and stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352057657,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/tool-call-turn/session.jsonl b/examples/acp-agent/tests/snapshots/tool-call-turn/session.jsonl
index f631c9bf54..3b0e93b464 100644
--- a/examples/acp-agent/tests/snapshots/tool-call-turn/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/tool-call-turn/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"e9421ff4-baae-4807-a7ea-fd8a65f2c897","createdAt":1783352044766,"cwd":"/tmp/acp-snap-cwd-OwUkBh"}
+{"type":"session","version":0,"id":"e9421ff4-baae-4807-a7ea-fd8a65f2c897","createdAt":1783352044766,"cwd":"/tmp/acp-snap-cwd-OwUkBh","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352044771,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352044771,"data":{"content":[{"type":"text","text":"Use the bash tool to run exactly: echo SNAPSHOT_OK. Then reply with the single word DONE and stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352044773,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/workflow-run/session.1.jsonl b/examples/acp-agent/tests/snapshots/workflow-run/session.1.jsonl
index 3d89428bbd..eb8d9ed63e 100644
--- a/examples/acp-agent/tests/snapshots/workflow-run/session.1.jsonl
+++ b/examples/acp-agent/tests/snapshots/workflow-run/session.1.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"583a4db2-3350-436c-b4a5-5615fd159052","createdAt":1783600636316,"cwd":"/var/folders/bn/vj1dvck95yd5jh3x4wskflxm0000gn/T/acp-snap-cwd-vdJYjz","parentSession":"3fd7d599-56b1-493a-930d-f1fc5e1556e8"}
+{"type":"session","version":0,"id":"583a4db2-3350-436c-b4a5-5615fd159052","createdAt":1783600636316,"cwd":"/var/folders/bn/vj1dvck95yd5jh3x4wskflxm0000gn/T/acp-snap-cwd-vdJYjz","parentSession":"3fd7d599-56b1-493a-930d-f1fc5e1556e8","delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783600636316,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783600636316,"data":{"content":[{"type":"text","text":"Reply with exactly the word WF_CHILD_OK and nothing else."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783600636316,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/workflow-run/session.jsonl b/examples/acp-agent/tests/snapshots/workflow-run/session.jsonl
index 3e0ae3da73..20f4e296cd 100644
--- a/examples/acp-agent/tests/snapshots/workflow-run/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/workflow-run/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"3fd7d599-56b1-493a-930d-f1fc5e1556e8","createdAt":1783600631835,"cwd":"/var/folders/bn/vj1dvck95yd5jh3x4wskflxm0000gn/T/acp-snap-cwd-vdJYjz"}
+{"type":"session","version":0,"id":"3fd7d599-56b1-493a-930d-f1fc5e1556e8","createdAt":1783600631835,"cwd":"/var/folders/bn/vj1dvck95yd5jh3x4wskflxm0000gn/T/acp-snap-cwd-vdJYjz","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783600631838,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783600631838,"data":{"content":[{"type":"text","text":"Use the workflow tool exactly once, with args omitted, meta set to { \"name\": \"snapshot-flow\", \"description\": \"one child for the snapshot\" }, and this EXACT script body (copy it verbatim):\nphase('Run')\nconst reply = await agent('Reply with exactly the word WF_CHILD_OK and nothing else.')\nreturn { reply }\nAfter the workflow returns, reply with the single word WORKFLOW_DONE and stop. Do not use any other tool."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783600631839,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/workspace-context/session.jsonl b/examples/acp-agent/tests/snapshots/workspace-context/session.jsonl
index f50e124b32..9e08a7800b 100644
--- a/examples/acp-agent/tests/snapshots/workspace-context/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/workspace-context/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}"}
+{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783778297065,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783778297066,"data":{"content":[{"type":"text","text":"Read nested/task.txt with the read tool, then reply DONE."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783778297069,"data":{"turn":1,"step":1}}
diff --git a/examples/acp-agent/tests/snapshots/workspace-edit/session.jsonl b/examples/acp-agent/tests/snapshots/workspace-edit/session.jsonl
index 6b9b03a95e..4a5b37a374 100644
--- a/examples/acp-agent/tests/snapshots/workspace-edit/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/workspace-edit/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"48aca674-000a-4583-810b-01f8785cef13","createdAt":1783352264076,"cwd":"/tmp/acp-snap-cwd-rxbEpP"}
+{"type":"session","version":0,"id":"48aca674-000a-4583-810b-01f8785cef13","createdAt":1783352264076,"cwd":"/tmp/acp-snap-cwd-rxbEpP","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352264080,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352264081,"data":{"content":[{"type":"text","text":"A file named greeting.txt in the current directory contains one word. Use the bash tool to append a second line containing the word WORLD to it (so it has two lines), then read the file back with `cat greeting.txt` to confirm, and reply with the single word DONE. Use a single bash call per action."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352264082,"data":{"turn":1,"step":1}}
diff --git a/examples/headless-agent/cordis.yml b/examples/headless-agent/cordis.yml
index 7f48c529c4..1cd161eea7 100644
--- a/examples/headless-agent/cordis.yml
+++ b/examples/headless-agent/cordis.yml
@@ -64,12 +64,14 @@
   config:
     provider: spawn
     toolName: subagent
+    maxDepth: 1
 
 - id: tool-subagent-fork
   name: '@deepseek-ai/dsh-tool-subagent'
   config:
     provider: fork
     toolName: subagent_fork
+    maxDepth: 1
 
 # The worker-thread workflow engine fans a model-written JavaScript script's
 # `agent()` calls out through the spawn backend.
diff --git a/examples/headless-agent/tests/snapshots/advanced-toolchain/session.1.jsonl b/examples/headless-agent/tests/snapshots/advanced-toolchain/session.1.jsonl
index b4e8cd6340..d8affeaab8 100644
--- a/examples/headless-agent/tests/snapshots/advanced-toolchain/session.1.jsonl
+++ b/examples/headless-agent/tests/snapshots/advanced-toolchain/session.1.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"22222222-2222-4222-8222-222222222222","createdAt":1783950001000,"cwd":"/tmp/advanced-headless","parentSession":"11111111-1111-4111-8111-111111111111"}
+{"type":"session","version":0,"id":"22222222-2222-4222-8222-222222222222","createdAt":1783950001000,"cwd":"/tmp/advanced-headless","parentSession":"11111111-1111-4111-8111-111111111111","delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783957884563,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783957884563,"data":{"content":[{"type":"text","text":"Reply with exactly DIRECT_CHILD_OK and nothing else."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783957884564,"data":{"turn":1,"step":1}}
diff --git a/examples/headless-agent/tests/snapshots/advanced-toolchain/session.2.jsonl b/examples/headless-agent/tests/snapshots/advanced-toolchain/session.2.jsonl
index d8d2e59e6e..f0b6154472 100644
--- a/examples/headless-agent/tests/snapshots/advanced-toolchain/session.2.jsonl
+++ b/examples/headless-agent/tests/snapshots/advanced-toolchain/session.2.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"33333333-3333-4333-8333-333333333333","createdAt":1783950002000,"cwd":"/tmp/advanced-headless","parentSession":"11111111-1111-4111-8111-111111111111"}
+{"type":"session","version":0,"id":"33333333-3333-4333-8333-333333333333","createdAt":1783950002000,"cwd":"/tmp/advanced-headless","parentSession":"11111111-1111-4111-8111-111111111111","delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783957884700,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783957884700,"data":{"content":[{"type":"text","text":"Reply with exactly WORKFLOW_CHILD_OK and nothing else."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783957884700,"data":{"turn":1,"step":1}}
diff --git a/examples/headless-agent/tests/snapshots/advanced-toolchain/session.jsonl b/examples/headless-agent/tests/snapshots/advanced-toolchain/session.jsonl
index e3849110ce..045d7879df 100644
--- a/examples/headless-agent/tests/snapshots/advanced-toolchain/session.jsonl
+++ b/examples/headless-agent/tests/snapshots/advanced-toolchain/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"11111111-1111-4111-8111-111111111111","createdAt":1783950000000,"cwd":"/tmp/advanced-headless"}
+{"type":"session","version":0,"id":"11111111-1111-4111-8111-111111111111","createdAt":1783950000000,"cwd":"/tmp/advanced-headless","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783957884479,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783957884479,"data":{"content":[{"type":"text","text":"Run this advanced flow exactly once: mount a no-op Cordis plugin named snapshot-marker; use run_code to inspect the live dynamic mounts through tools.cordis_inspect; delegate once to a direct spawn child; run one workflow that delegates to another spawn child; unmount dyn-1; then reply with exactly ADVANCED_HEADLESS_OK."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783957884486,"data":{"turn":1,"step":1}}
diff --git a/examples/tui-agent/tests/snapshots/bash-terminal-card/session.jsonl b/examples/tui-agent/tests/snapshots/bash-terminal-card/session.jsonl
index e53f4b3da3..5c3bba5676 100644
--- a/examples/tui-agent/tests/snapshots/bash-terminal-card/session.jsonl
+++ b/examples/tui-agent/tests/snapshots/bash-terminal-card/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"e128dda9-ed11-4868-8266-0ef90d03c3d6","createdAt":1783352050748,"cwd":"/tmp/acp-snap-cwd-mrFUuk"}
+{"type":"session","version":0,"id":"e128dda9-ed11-4868-8266-0ef90d03c3d6","createdAt":1783352050748,"cwd":"/tmp/acp-snap-cwd-mrFUuk","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352050753,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352050753,"data":{"content":[{"type":"text","text":"Use the bash tool to run exactly: echo TERMINAL_OK. Then reply with the single word DONE and stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352050755,"data":{"turn":1,"step":1}}
diff --git a/examples/tui-agent/tests/snapshots/code-mode/session.jsonl b/examples/tui-agent/tests/snapshots/code-mode/session.jsonl
index 0fe57055e8..8ee160ba26 100644
--- a/examples/tui-agent/tests/snapshots/code-mode/session.jsonl
+++ b/examples/tui-agent/tests/snapshots/code-mode/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"94cd1ae4-e1d1-4ec8-9d27-50a1f849b6b3","createdAt":1783611771392,"cwd":"/var/folders/2c/psb0_fmx7hbgz558xjt_f0l00000gn/T/acp-snap-cwd-BteTVR"}
+{"type":"session","version":0,"id":"94cd1ae4-e1d1-4ec8-9d27-50a1f849b6b3","createdAt":1783611771392,"cwd":"/var/folders/2c/psb0_fmx7hbgz558xjt_f0l00000gn/T/acp-snap-cwd-BteTVR","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783611771394,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783611771394,"data":{"content":[{"type":"text","text":"Using ONE run_code program: call the bash tool twice — exactly `echo CODE_ONE` then exactly `echo CODE_TWO` — and return the two outputs joined with a plus sign. Then reply with that joined string only and stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783611771396,"data":{"turn":1,"step":1}}
diff --git a/examples/tui-agent/tests/snapshots/cordis-dynamic-toolchain/session.1.jsonl b/examples/tui-agent/tests/snapshots/cordis-dynamic-toolchain/session.1.jsonl
index 25a6f76411..26519d458e 100644
--- a/examples/tui-agent/tests/snapshots/cordis-dynamic-toolchain/session.1.jsonl
+++ b/examples/tui-agent/tests/snapshots/cordis-dynamic-toolchain/session.1.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"22222222-2222-4222-8222-222222222222","createdAt":1783950001000,"cwd":"/tmp/advanced-acp","parentSession":"11111111-1111-4111-8111-111111111111"}
+{"type":"session","version":0,"id":"22222222-2222-4222-8222-222222222222","createdAt":1783950001000,"cwd":"/tmp/advanced-acp","parentSession":"11111111-1111-4111-8111-111111111111","delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783957884563,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783957884563,"data":{"content":[{"type":"text","text":"Reply with exactly DIRECT_CHILD_OK and nothing else."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783957884564,"data":{"turn":1,"step":1}}
diff --git a/examples/tui-agent/tests/snapshots/cordis-dynamic-toolchain/session.2.jsonl b/examples/tui-agent/tests/snapshots/cordis-dynamic-toolchain/session.2.jsonl
index 45d9043a4a..9daa8958dc 100644
--- a/examples/tui-agent/tests/snapshots/cordis-dynamic-toolchain/session.2.jsonl
+++ b/examples/tui-agent/tests/snapshots/cordis-dynamic-toolchain/session.2.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"33333333-3333-4333-8333-333333333333","createdAt":1783950002000,"cwd":"/tmp/advanced-acp","parentSession":"11111111-1111-4111-8111-111111111111"}
+{"type":"session","version":0,"id":"33333333-3333-4333-8333-333333333333","createdAt":1783950002000,"cwd":"/tmp/advanced-acp","parentSession":"11111111-1111-4111-8111-111111111111","delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783957884700,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783957884700,"data":{"content":[{"type":"text","text":"Reply with exactly WORKFLOW_CHILD_OK and nothing else."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783957884700,"data":{"turn":1,"step":1}}
diff --git a/examples/tui-agent/tests/snapshots/cordis-dynamic-toolchain/session.jsonl b/examples/tui-agent/tests/snapshots/cordis-dynamic-toolchain/session.jsonl
index 39f867984a..46c8e41257 100644
--- a/examples/tui-agent/tests/snapshots/cordis-dynamic-toolchain/session.jsonl
+++ b/examples/tui-agent/tests/snapshots/cordis-dynamic-toolchain/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"11111111-1111-4111-8111-111111111111","createdAt":1783950000000,"cwd":"/tmp/advanced-acp"}
+{"type":"session","version":0,"id":"11111111-1111-4111-8111-111111111111","createdAt":1783950000000,"cwd":"/tmp/advanced-acp","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783957884479,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783957884479,"data":{"content":[{"type":"text","text":"Run this advanced flow exactly once: mount a no-op Cordis plugin named snapshot-marker; use run_code to inspect the live dynamic mounts through tools.cordis_inspect; delegate once to a direct spawn child; run one workflow that delegates to another spawn child; unmount dyn-1; then reply with exactly ADVANCED_ACP_OK."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783957884486,"data":{"turn":1,"step":1}}
diff --git a/examples/tui-agent/tests/snapshots/dynamic-workflow/session.1.jsonl b/examples/tui-agent/tests/snapshots/dynamic-workflow/session.1.jsonl
index 3d89428bbd..eb8d9ed63e 100644
--- a/examples/tui-agent/tests/snapshots/dynamic-workflow/session.1.jsonl
+++ b/examples/tui-agent/tests/snapshots/dynamic-workflow/session.1.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"583a4db2-3350-436c-b4a5-5615fd159052","createdAt":1783600636316,"cwd":"/var/folders/bn/vj1dvck95yd5jh3x4wskflxm0000gn/T/acp-snap-cwd-vdJYjz","parentSession":"3fd7d599-56b1-493a-930d-f1fc5e1556e8"}
+{"type":"session","version":0,"id":"583a4db2-3350-436c-b4a5-5615fd159052","createdAt":1783600636316,"cwd":"/var/folders/bn/vj1dvck95yd5jh3x4wskflxm0000gn/T/acp-snap-cwd-vdJYjz","parentSession":"3fd7d599-56b1-493a-930d-f1fc5e1556e8","delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783600636316,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783600636316,"data":{"content":[{"type":"text","text":"Reply with exactly the word WF_CHILD_OK and nothing else."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783600636316,"data":{"turn":1,"step":1}}
diff --git a/examples/tui-agent/tests/snapshots/dynamic-workflow/session.jsonl b/examples/tui-agent/tests/snapshots/dynamic-workflow/session.jsonl
index 3e0ae3da73..20f4e296cd 100644
--- a/examples/tui-agent/tests/snapshots/dynamic-workflow/session.jsonl
+++ b/examples/tui-agent/tests/snapshots/dynamic-workflow/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"3fd7d599-56b1-493a-930d-f1fc5e1556e8","createdAt":1783600631835,"cwd":"/var/folders/bn/vj1dvck95yd5jh3x4wskflxm0000gn/T/acp-snap-cwd-vdJYjz"}
+{"type":"session","version":0,"id":"3fd7d599-56b1-493a-930d-f1fc5e1556e8","createdAt":1783600631835,"cwd":"/var/folders/bn/vj1dvck95yd5jh3x4wskflxm0000gn/T/acp-snap-cwd-vdJYjz","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783600631838,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783600631838,"data":{"content":[{"type":"text","text":"Use the workflow tool exactly once, with args omitted, meta set to { \"name\": \"snapshot-flow\", \"description\": \"one child for the snapshot\" }, and this EXACT script body (copy it verbatim):\nphase('Run')\nconst reply = await agent('Reply with exactly the word WF_CHILD_OK and nothing else.')\nreturn { reply }\nAfter the workflow returns, reply with the single word WORKFLOW_DONE and stop. Do not use any other tool."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783600631839,"data":{"turn":1,"step":1}}
diff --git a/examples/tui-agent/tests/snapshots/multi-turn-conversation/session.jsonl b/examples/tui-agent/tests/snapshots/multi-turn-conversation/session.jsonl
index cd32072eaa..83ccf18a3f 100644
--- a/examples/tui-agent/tests/snapshots/multi-turn-conversation/session.jsonl
+++ b/examples/tui-agent/tests/snapshots/multi-turn-conversation/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"228b7b82-84ed-49b7-a567-981c03b28c77","createdAt":1783352113760,"cwd":"/tmp/acp-snap-cwd-aN2GRR"}
+{"type":"session","version":0,"id":"228b7b82-84ed-49b7-a567-981c03b28c77","createdAt":1783352113760,"cwd":"/tmp/acp-snap-cwd-aN2GRR","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352113765,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352113765,"data":{"content":[{"type":"text","text":"Reply with exactly the word: ONE. No tools."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352113767,"data":{"turn":1,"step":1}}
diff --git a/examples/tui-agent/tests/snapshots/parallel-file-reads/session.jsonl b/examples/tui-agent/tests/snapshots/parallel-file-reads/session.jsonl
index 81503dc4cf..e83f0cd59c 100644
--- a/examples/tui-agent/tests/snapshots/parallel-file-reads/session.jsonl
+++ b/examples/tui-agent/tests/snapshots/parallel-file-reads/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}"}
+{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":0,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":0,"data":{"content":[{"type":"text","text":"Use the read tool twice in the same assistant message: read a.txt and b.txt. Then reply DONE."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":0,"data":{"turn":1,"step":1}}
diff --git a/examples/tui-agent/tests/snapshots/todo-plan/session.jsonl b/examples/tui-agent/tests/snapshots/todo-plan/session.jsonl
index 909afc44cd..cea8a4fa88 100644
--- a/examples/tui-agent/tests/snapshots/todo-plan/session.jsonl
+++ b/examples/tui-agent/tests/snapshots/todo-plan/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"b0f1f758-dcf0-474e-851d-e62c11ec0a09","createdAt":1783352057652,"cwd":"/tmp/acp-snap-cwd-AYilT7"}
+{"type":"session","version":0,"id":"b0f1f758-dcf0-474e-851d-e62c11ec0a09","createdAt":1783352057652,"cwd":"/tmp/acp-snap-cwd-AYilT7","delegationDepth":0}
 {"type":"turn/start","seq":0,"time":1783352057655,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783352057655,"data":{"content":[{"type":"text","text":"Use the todo_write tool to record a plan with exactly three todos: \"read the code\" (in_progress), \"write the fix\" (pending), \"run the tests\" (pending). Send all three in one todo_write call. Then reply with the single word DONE and stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783352057657,"data":{"turn":1,"step":1}}
diff --git a/packages/cordis/tool-cordis/src/api-catalog.ts b/packages/cordis/tool-cordis/src/api-catalog.ts
index efb29e547d..e4eb85c043 100644
--- a/packages/cordis/tool-cordis/src/api-catalog.ts
+++ b/packages/cordis/tool-cordis/src/api-catalog.ts
@@ -367,7 +367,7 @@ export const SERVICE_API: readonly ServiceApiEntry[] = [
     methods: [
       {
         signature: 'create(id?: SessionId, options?: CreateSessionOptions): Session',
-        jsDoc: '/**\n * Create a session owned by the calling fiber: disposing that fiber stops\n * event notification and removes the session from the store. `options.seed`\n * populates the session with a copy of those events (replay/fork);\n * `options.meta` attaches creation metadata (validated absolute `cwd`,\n * `parentSession` lineage) as the immutable {@link SessionHeader} (the store\n * fills `version`/`id`/`createdAt`).\n *\n * For an agent whose session must be torn down IN ORDER with its loop (so the\n * loop\'s final flush is captured before the store attachment ends), do NOT use this\n * — fold the session lifecycle into the agent\'s own effect via\n * {@link prepare} + {@link enter} + {@link announce} (see\n * `dsh-agent-loop`\'s creation transaction).\n *\n * @param id - the session id; omitted, the store mints `session-<n>`.\n * @param options - seed events and/or creation metadata for the header.\n * @returns the live session, already entered and announced.\n * @throws if a session with `id` already exists, metadata is not a plain\n *   lossless-JSON record with valid scalar fields, or `meta.cwd` is a\n *   non-absolute path (storage backends key directories off it).\n */',
+        jsDoc: '/**\n * Create a session owned by the calling fiber: disposing that fiber stops\n * event notification and removes the session from the store. `options.seed`\n * populates the session with a copy of those events (replay/fork);\n * `options.meta` attaches creation metadata (validated absolute `cwd`, seed\n * and parent lineage, and delegation depth) as the immutable\n * {@link SessionHeader} (the store fills `version`/`id`/`createdAt`).\n *\n * For an agent whose session must be torn down IN ORDER with its loop (so the\n * loop\'s final flush is captured before the store attachment ends), do NOT use this\n * — fold the session lifecycle into the agent\'s own effect via\n * {@link prepare} + {@link enter} + {@link announce} (see\n * `dsh-agent-loop`\'s creation transaction).\n *\n * @param id - the session id; omitted, the store mints `session-<n>`.\n * @param options - seed events and/or creation metadata for the header.\n * @returns the live session, already entered and announced.\n * @throws if a session with `id` already exists, metadata is not a plain\n *   lossless-JSON record with valid scalar fields, or `meta.cwd` is a\n *   non-absolute path (storage backends key directories off it).\n */',
       },
       {
         signature: 'prepare(id?: SessionId, options?: CreateSessionOptions): Session',
@@ -1093,11 +1093,11 @@ export const TYPE_API: readonly TypeApiEntry[] = [
   },
   {
     name: 'CreateAgentOptions',
-    declaration: 'export interface CreateAgentOptions {\n    readonly sessionId: SessionId;\n    readonly meta?: {\n        readonly cwd?: string;\n        readonly parentSession?: SessionId;\n        readonly seedLength?: number;\n    };\n    readonly seed?: readonly SessionEvent[];\n    readonly agentOptions?: AgentOptions;\n    readonly signal?: AbortSignal;\n    readonly setup?: (agentCtx: Context) => Promise<void> | void;\n}',
+    declaration: 'export interface CreateAgentOptions {\n    readonly sessionId: SessionId;\n    readonly meta?: {\n        readonly cwd?: string;\n        readonly parentSession?: SessionId;\n        readonly seedLength?: number;\n        readonly delegationDepth?: number;\n    };\n    readonly seed?: readonly SessionEvent[];\n    readonly agentOptions?: AgentOptions;\n    readonly signal?: AbortSignal;\n    readonly setup?: (agentCtx: Context) => Promise<void> | void;\n}',
   },
   {
     name: 'CreateSessionOptions',
-    declaration: 'export interface CreateSessionOptions {\n    readonly seed?: readonly SessionEvent[];\n    readonly meta?: {\n        readonly cwd?: string;\n        readonly parentSession?: SessionId;\n        readonly createdAt?: number;\n        readonly seedLength?: number;\n    };\n}',
+    declaration: 'export interface CreateSessionOptions {\n    readonly seed?: readonly SessionEvent[];\n    readonly meta?: {\n        readonly cwd?: string;\n        readonly parentSession?: SessionId;\n        readonly createdAt?: number;\n        readonly seedLength?: number;\n        readonly delegationDepth?: number;\n    };\n}',
   },
   {
     name: 'DiffCallView',
@@ -1321,7 +1321,7 @@ export const TYPE_API: readonly TypeApiEntry[] = [
   },
   {
     name: 'SessionHeader',
-    declaration: 'export interface SessionHeader {\n    readonly version: number;\n    readonly id: SessionId;\n    readonly createdAt: number;\n    readonly cwd?: string;\n    readonly parentSession?: SessionId;\n    readonly seedLength?: number;\n}',
+    declaration: 'export interface SessionHeader {\n    readonly version: number;\n    readonly id: SessionId;\n    readonly createdAt: number;\n    readonly cwd?: string;\n    readonly parentSession?: SessionId;\n    readonly seedLength?: number;\n    readonly delegationDepth?: number;\n}',
   },
   {
     name: 'SessionId',
diff --git a/packages/core/agent-loop/src/index.ts b/packages/core/agent-loop/src/index.ts
index 2a77afc983..7268182552 100644
--- a/packages/core/agent-loop/src/index.ts
+++ b/packages/core/agent-loop/src/index.ts
@@ -620,12 +620,7 @@ export class AgentLoop extends Service implements AgentFactory {
       transaction.assertActive()
       const session = this.runtime.ctx.sessions.prepare(options.resumeSessionId, {
         seed: loaded.events,
-        meta: {
-          createdAt: loaded.meta.createdAt,
-          ...loaded.meta.cwd === undefined ? {} : { cwd: loaded.meta.cwd },
-          ...loaded.meta.parentSession === undefined ? {} : { parentSession: loaded.meta.parentSession },
-          ...loaded.meta.seedLength === undefined ? {} : { seedLength: loaded.meta.seedLength },
-        },
+        meta: loaded.meta,
       })
       const agent = transaction.prepare(agentOptions, session, this.maxParallelToolCalls)
       await transaction.waitFor(options.setup?.(agent.ctx))
diff --git a/packages/core/agent-loop/tests/resume.spec.ts b/packages/core/agent-loop/tests/resume.spec.ts
index 57635bbe5f..0547388d96 100644
--- a/packages/core/agent-loop/tests/resume.spec.ts
+++ b/packages/core/agent-loop/tests/resume.spec.ts
@@ -411,7 +411,7 @@ describe('the session-persistence Agent Note: AgentLoop factory create/resume',
     await ctx.fiber.dispose()
   })
 
-  it('resume of a forked session preserves the parentSession lineage and seed boundary in the header', async () => {
+  it('resume of a forked session preserves the lineage, seed boundary, and delegation depth in the header', async () => {
     // Lifecycle 1: persist a FORKED session (carries parentSession + seedLength
     // in its header) by creating it with a complete-turn seed — the write path
     // materializes the fork (header + seed) on disk.
@@ -423,7 +423,7 @@ describe('the session-persistence Agent Note: AgentLoop factory create/resume',
     const { ctx: ctx1, root } = await persistentHarness(adapter1)
     const forked = ctx1.sessions.create(SessionId('forked-sess'), {
       seed,
-      meta: { cwd: '/w', parentSession: SessionId('parent-sess'), seedLength: seed.length },
+      meta: { cwd: '/w', parentSession: SessionId('parent-sess'), seedLength: seed.length, delegationDepth: 1 },
     })
     await ctx1.parallel('session/flush', forked)
     await ctx1.fiber.dispose()
@@ -447,6 +447,9 @@ describe('the session-persistence Agent Note: AgentLoop factory create/resume',
     expect(a2.session.header.parentSession).toBe('parent-sess')
     expect(a2.session.header.cwd).toBe('/w')
     expect(a2.session.header.seedLength).toBe(seed.length)
+    // The recursion budget survives resume — a dropped depth would let a
+    // resumed child delegate as if it were top-level.
+    expect(a2.session.header.delegationDepth).toBe(1)
     await ctx2.fiber.dispose()
   })
 
diff --git a/packages/core/agent/src/index.ts b/packages/core/agent/src/index.ts
index 75f00daebb..061ddae53f 100644
--- a/packages/core/agent/src/index.ts
+++ b/packages/core/agent/src/index.ts
@@ -46,15 +46,21 @@ export interface CreateAgentOptions {
   readonly sessionId: SessionId
   /**
    * Session creation metadata: validated absolute `cwd`, `parentSession`
-   * fork lineage, and the `seedLength` seed boundary. Mirrors the
-   * `cwd`/`parentSession`/`seedLength` fields of
+   * fork lineage, the `seedLength` seed boundary, and the `delegationDepth`
+   * recursion budget. Mirrors the
+   * `cwd`/`parentSession`/`seedLength`/`delegationDepth` fields of
    * {@link CreateSessionOptions.meta} in dsh-session (the internal-only
    * `createdAt`, used when reconstructing a persisted session, is deliberately
    * excluded — a factory caller never sets it). This is durable session data,
    * so the session boundary validates and snapshots it before asynchronous
    * setup begins.
    */
-  readonly meta?: { readonly cwd?: string; readonly parentSession?: SessionId; readonly seedLength?: number }
+  readonly meta?: {
+    readonly cwd?: string
+    readonly parentSession?: SessionId
+    readonly seedLength?: number
+    readonly delegationDepth?: number
+  }
   /**
    * Seed events to reconstruct the child session's log from (the fork lineage
    * primitive). When present, the factory creates the session with this event
diff --git a/packages/core/session/README.md b/packages/core/session/README.md
index 1b584ac3d9..f9ce78ad14 100644
--- a/packages/core/session/README.md
+++ b/packages/core/session/README.md
@@ -8,7 +8,7 @@ Creates and holds event-sourced `Session` instances. Persistence is intentionall
 
 ### Public API
 
-- `ctx.sessions.create(id?, { seed?, meta? }?)` validates and detaches durable seed/header data, fills the version and id, defaults `createdAt` to now, publishes the session, and binds it to the calling fiber. Persisted reconstruction supplies its original `createdAt` and `seedLength`.
+- `ctx.sessions.create(id?, { seed?, meta? }?)` validates and detaches durable seed/header data, fills the version and id, defaults `createdAt` to now, publishes the session, and binds it to the calling fiber. Persisted reconstruction supplies its original `createdAt`, `seedLength`, and `delegationDepth`.
 - `ctx.sessions.flush(session)` dispatches the awaited parallel durability checkpoint through the session's captured scope. Every listener starts and the call waits for all to settle before reporting failure; unpublished, detached, and stale objects reject.
 - `ctx.sessions.fork(source, boundary?, childSessionId?): Session` — Resolve a live session object or id, select a seed through the inclusive `boundary` event seq (default: current last event), require that boundary to be `turn/end`, and create a live child session with lineage metadata.
 - `ctx.sessions.get(id: SessionId): Session | undefined`
@@ -38,7 +38,7 @@ Plain class (not a Cordis Service). Create via `ctx.sessions.create()`.
 - `session.surface` exposes the readonly `SessionSurface` view owned by the session's single incremental surface manager; `replaceGeneration` changes on every committed rewrite.
 - `session.events` is a cached frozen snapshot invalidated by append; accepted events remain deeply frozen.
 - `session.seq`, `session.id` — current sequence and readonly typed identity.
-- `session.header: SessionHeader` — detached, deep-frozen creation metadata (`version`, `id`, `createdAt`, optional `cwd`/`parentSession`/`seedLength`). Construction validates the durable record and requires its id to match `session.id`.
+- `session.header: SessionHeader` — detached, deep-frozen creation metadata (`version`, `id`, `createdAt`, optional `cwd`/`parentSession`/`seedLength`/`delegationDepth`). Construction validates the durable record and requires its id to match `session.id`.
 
 ### Lossless JSON utilities
 
@@ -73,7 +73,7 @@ Every `SessionEvent` carries two optional top-level fields (structural metadata)
 
 ### Metadata types (`types.ts`)
 
-- `SessionHeader` — session metadata written once when published as `Session.header`, where detachment and deep-freezing enforce immutability at runtime: `{ version, id, createdAt, cwd?, parentSession?, seedLength? }`. Persistence loaders may return mutable detached copies of the same data type. Owned here (beside `SessionId`) because `Session.header` is typed by it; persistence backends re-export it rather than own it (which would force a package cycle).
+- `SessionHeader` — session metadata written once when published as `Session.header`, where detachment and deep-freezing enforce immutability at runtime: `{ version, id, createdAt, cwd?, parentSession?, seedLength?, delegationDepth? }`. Persistence loaders may return mutable detached copies of the same data type. Owned here (beside `SessionId`) because `Session.header` is typed by it; persistence backends re-export it rather than own it (which would force a package cycle).
 
 ### Extension points
 
diff --git a/packages/core/session/src/index.ts b/packages/core/session/src/index.ts
index 99024999e9..9b2eb74a37 100644
--- a/packages/core/session/src/index.ts
+++ b/packages/core/session/src/index.ts
@@ -113,6 +113,10 @@ function snapshotSessionHeader(id: SessionId, source?: SessionHeader): SessionHe
     && (typeof record.seedLength !== 'number' || !Number.isSafeInteger(record.seedLength) || record.seedLength < 0)) {
     throw new Error('session header seedLength must be a non-negative safe integer')
   }
+  if (record.delegationDepth !== undefined
+    && (typeof record.delegationDepth !== 'number' || !Number.isSafeInteger(record.delegationDepth) || record.delegationDepth < 0)) {
+    throw new Error('session header delegationDepth must be a non-negative safe integer')
+  }
   return deepFreeze(record as unknown as SessionHeader)
 }
 
@@ -558,9 +562,9 @@ export class SessionStore extends Service {
    * Create a session owned by the calling fiber: disposing that fiber stops
    * event notification and removes the session from the store. `options.seed`
    * populates the session with a copy of those events (replay/fork);
-   * `options.meta` attaches creation metadata (validated absolute `cwd`,
-   * `parentSession` lineage) as the immutable {@link SessionHeader} (the store
-   * fills `version`/`id`/`createdAt`).
+   * `options.meta` attaches creation metadata (validated absolute `cwd`, seed
+   * and parent lineage, and delegation depth) as the immutable
+   * {@link SessionHeader} (the store fills `version`/`id`/`createdAt`).
    *
    * For an agent whose session must be torn down IN ORDER with its loop (so the
    * loop's final flush is captured before the store attachment ends), do NOT use this
@@ -622,6 +626,7 @@ export class SessionStore extends Service {
       ...meta?.cwd === undefined ? {} : { cwd: meta.cwd },
       ...meta?.parentSession === undefined ? {} : { parentSession: meta.parentSession },
       ...meta?.seedLength === undefined ? {} : { seedLength: meta.seedLength },
+      ...meta?.delegationDepth === undefined ? {} : { delegationDepth: meta.delegationDepth },
     }
     return new Session(sessionId, seed, header)
   }
diff --git a/packages/core/session/src/types.ts b/packages/core/session/src/types.ts
index 7188c58b97..af8a04571e 100644
--- a/packages/core/session/src/types.ts
+++ b/packages/core/session/src/types.ts
@@ -47,6 +47,12 @@ export interface SessionHeader {
    * boundary lets resume and replay distinguish parent history from child work.
    */
   readonly seedLength?: number
+  /**
+   * Delegation depth: absent (zero) for a top-level session, parent depth + 1
+   * for a subagent child. Persisted so a recursion budget survives restart and
+   * resume — a runtime-only depth would reset a resumed child to top-level.
+   */
+  readonly delegationDepth?: number
 }
 
 /**
@@ -66,6 +72,7 @@ export interface CreateSessionOptions {
     readonly parentSession?: SessionId
     readonly createdAt?: number
     readonly seedLength?: number
+    readonly delegationDepth?: number
   }
 }
 
diff --git a/packages/core/session/tests/session.spec.ts b/packages/core/session/tests/session.spec.ts
index 588c8048f4..a17981146d 100644
--- a/packages/core/session/tests/session.spec.ts
+++ b/packages/core/session/tests/session.spec.ts
@@ -881,6 +881,19 @@ describe('SessionStore', () => {
     })
   })
 
+  it('attaches delegationDepth from meta to the header', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const session = ctx.sessions.create(SessionId('delegated-child'), {
+      meta: { parentSession: SessionId('parent'), delegationDepth: 2 },
+    })
+    expect(session.header).toMatchObject({
+      id: 'delegated-child',
+      parentSession: 'parent',
+      delegationDepth: 2,
+    })
+  })
+
   it('rejects non-JSON and invalid scalar session metadata', async () => {
     const ctx = new Context()
     await ctx.plugin(SessionStore)
@@ -892,6 +905,9 @@ describe('SessionStore', () => {
       { meta: { seedLength: '1' }, error: /seedLength must be a non-negative safe integer/ },
       { meta: { seedLength: 0.5 }, error: /seedLength must be a non-negative safe integer/ },
       { meta: { seedLength: -1 }, error: /seedLength must be a non-negative safe integer/ },
+      { meta: { delegationDepth: '1' }, error: /delegationDepth must be a non-negative safe integer/ },
+      { meta: { delegationDepth: 0.5 }, error: /delegationDepth must be a non-negative safe integer/ },
+      { meta: { delegationDepth: -1 }, error: /delegationDepth must be a non-negative safe integer/ },
     ]
 
     for (const [index, { meta, error }] of cases.entries()) {
diff --git a/packages/session-persistence/session-persistence-jsonl/README.md b/packages/session-persistence/session-persistence-jsonl/README.md
index cf733b85d4..d6130d414a 100644
--- a/packages/session-persistence/session-persistence-jsonl/README.md
+++ b/packages/session-persistence/session-persistence-jsonl/README.md
@@ -10,7 +10,7 @@ The JSONL durable session-persistence backend — a concrete `SessionPersistence
     <encoded-id>.jsonl           # header line + one SessionEvent per line (verbatim)
 ```
 
-- The first `.jsonl` line is the immutable `SessionHeader` tagged `{ type: 'session', version, id, cwd?, createdAt, parentSession?, seedLength? }`; every subsequent line is one `SessionEvent` JSON, **verbatim including `assistant/chunk`** so `seq` stays contiguous (`events[i].seq === i`).
+- The first `.jsonl` line is the immutable `SessionHeader` tagged `{ type: 'session', version, id, cwd?, createdAt, parentSession?, seedLength?, delegationDepth }`. `delegationDepth` is required on disk and is `0` for a top-level session; a missing or invalid value rejects the log. Every subsequent line is one `SessionEvent` JSON, **verbatim including `assistant/chunk`** so `seq` stays contiguous (`events[i].seq === i`).
 - Session ids are unvalidated branded strings, so they are percent-encoded to a single safe path segment before use (no traversal, no collision).
 
 ## Config
diff --git a/packages/session-persistence/session-persistence-jsonl/src/format.ts b/packages/session-persistence/session-persistence-jsonl/src/format.ts
index 39bdecf751..3349eac12e 100644
--- a/packages/session-persistence/session-persistence-jsonl/src/format.ts
+++ b/packages/session-persistence/session-persistence-jsonl/src/format.ts
@@ -25,6 +25,7 @@ export interface HeaderLine {
   cwd?: string
   parentSession?: SessionId
   seedLength?: number
+  delegationDepth: number
 }
 
 /**
@@ -41,6 +42,7 @@ export function toHeaderLine(header: SessionHeader): HeaderLine {
     ...header.cwd !== undefined ? { cwd: header.cwd } : {},
     ...header.parentSession !== undefined ? { parentSession: header.parentSession } : {},
     ...header.seedLength !== undefined ? { seedLength: header.seedLength } : {},
+    delegationDepth: header.delegationDepth ?? 0,
   }
 }
 
@@ -57,6 +59,7 @@ export function fromHeaderLine(line: HeaderLine): SessionHeader {
     ...line.cwd !== undefined ? { cwd: line.cwd } : {},
     ...line.parentSession !== undefined ? { parentSession: line.parentSession } : {},
     ...line.seedLength !== undefined ? { seedLength: line.seedLength } : {},
+    delegationDepth: line.delegationDepth,
   }
 }
 
@@ -68,6 +71,10 @@ function isHeaderLine(value: unknown): value is HeaderLine {
     && typeof (value as { version?: unknown }).version === 'number'
     && typeof (value as { id?: unknown }).id === 'string'
     && typeof (value as { createdAt?: unknown }).createdAt === 'number'
+    && typeof (value as { delegationDepth?: unknown }).delegationDepth === 'number'
+    && Number.isSafeInteger((value as { delegationDepth: number }).delegationDepth)
+    && (value as { delegationDepth: number }).delegationDepth >= 0
+    && !Object.is((value as { delegationDepth: number }).delegationDepth, -0)
   )
 }
 
diff --git a/packages/session-persistence/session-persistence-jsonl/tests/jsonl.spec.ts b/packages/session-persistence/session-persistence-jsonl/tests/jsonl.spec.ts
index e7dc469132..9a236c5397 100644
--- a/packages/session-persistence/session-persistence-jsonl/tests/jsonl.spec.ts
+++ b/packages/session-persistence/session-persistence-jsonl/tests/jsonl.spec.ts
@@ -461,9 +461,30 @@ describe('SessionPersistenceJsonl: scanLog unit', () => {
     expect(() => scanLog(Buffer.from('{"type":"event"}\n'))).toThrow(/session header/)
   })
 
+  it.each([
+    ['missing', undefined],
+    ['a string', '1'],
+    ['fractional', 1.5],
+    ['negative', -1],
+  ])('rejects a session header with %s delegationDepth', (_label, delegationDepth) => {
+    const log = JSON.stringify({
+      type: 'session',
+      version: 0,
+      id: 'invalid-depth',
+      createdAt: 1,
+      ...delegationDepth === undefined ? {} : { delegationDepth },
+    }) + '\n'
+    expect(() => scanLog(Buffer.from(log))).toThrow(/session header/)
+  })
+
+  it('rejects a session header with negative-zero delegationDepth', () => {
+    const log = '{"type":"session","version":0,"id":"invalid-depth","createdAt":1,"delegationDepth":-0}\n'
+    expect(() => scanLog(Buffer.from(log))).toThrow(/session header/)
+  })
+
   it('a seq gap after the last turn/end bounds the preserved tail (torn fragment tolerated)', () => {
     const log = [
-      JSON.stringify({ type: 'session', version: 0, id: 'g', createdAt: 1 }),
+      JSON.stringify({ type: 'session', version: 0, id: 'g', createdAt: 1, delegationDepth: 0 }),
       JSON.stringify({ type: 'turn/start', seq: 0, time: 1, data: { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } } }),
       JSON.stringify({ type: 'step/start', seq: 2, time: 2, data: { turn: 1, step: 1 } }), // gap: missing seq 1
     ].join('\n') + '\n'
@@ -475,7 +496,7 @@ describe('SessionPersistenceJsonl: scanLog unit', () => {
 
   it('rejects a seq gap BEFORE a later committed turn/end (committed data damaged)', () => {
     const log = [
-      JSON.stringify({ type: 'session', version: 0, id: 'g2', createdAt: 1 }),
+      JSON.stringify({ type: 'session', version: 0, id: 'g2', createdAt: 1, delegationDepth: 0 }),
       JSON.stringify({ type: 'turn/start', seq: 0, time: 1, data: { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } } }),
       JSON.stringify({ type: 'step/start', seq: 2, time: 2, data: { turn: 1, step: 1 } }), // gap: missing seq 1
       JSON.stringify({ type: 'turn/end', seq: 3, time: 3, data: { turn: 1, reason: { kind: 'completed' } } }),
@@ -487,7 +508,7 @@ describe('SessionPersistenceJsonl: scanLog unit', () => {
 
   it('rejects a corrupt line BEFORE a later committed turn/end (committed data damaged)', () => {
     const log = [
-      JSON.stringify({ type: 'session', version: 0, id: 'c', createdAt: 1 }),
+      JSON.stringify({ type: 'session', version: 0, id: 'c', createdAt: 1, delegationDepth: 0 }),
       '{not json', // corrupt, sits in the committed region (a turn/end follows)
       JSON.stringify({ type: 'turn/end', seq: 1, time: 2, data: { turn: 1, reason: { kind: 'completed' } } }),
     ].join('\n') + '\n'
@@ -495,7 +516,7 @@ describe('SessionPersistenceJsonl: scanLog unit', () => {
   })
 
   it('a header-only log (no event lines at all) preserves nothing — committedBytes is the header', () => {
-    const log = JSON.stringify({ type: 'session', version: 0, id: 'h0', createdAt: 1 }) + '\n'
+    const log = JSON.stringify({ type: 'session', version: 0, id: 'h0', createdAt: 1, delegationDepth: 0 }) + '\n'
     const scanned = scanLog(Buffer.from(log))
     expect(scanned.events).toEqual([])
     // committedBytes falls back to the header line's end (no preserved events).
@@ -504,7 +525,7 @@ describe('SessionPersistenceJsonl: scanLog unit', () => {
 
   it('a corrupt line after the last turn/end bounds the preserved tail', () => {
     const log = [
-      JSON.stringify({ type: 'session', version: 0, id: 'c2', createdAt: 1 }),
+      JSON.stringify({ type: 'session', version: 0, id: 'c2', createdAt: 1, delegationDepth: 0 }),
       JSON.stringify({ type: 'turn/start', seq: 0, time: 1, data: { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } } }),
       '{not json', // corrupt crash fragment, no turn/end committed
     ].join('\n') + '\n'
@@ -515,7 +536,7 @@ describe('SessionPersistenceJsonl: scanLog unit', () => {
 
   it('tolerates a seq gap AFTER a turn/end (uncommitted tail)', () => {
     const log = [
-      JSON.stringify({ type: 'session', version: 0, id: 't', createdAt: 1 }),
+      JSON.stringify({ type: 'session', version: 0, id: 't', createdAt: 1, delegationDepth: 0 }),
       JSON.stringify({ type: 'turn/start', seq: 0, time: 1, data: { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } } }),
       JSON.stringify({ type: 'turn/end', seq: 1, time: 2, data: { turn: 1, reason: { kind: 'completed' } } }),
       JSON.stringify({ type: 'step/start', seq: 9, time: 3, data: { turn: 2, step: 1 } }), // gap in uncommitted tail
@@ -593,7 +614,7 @@ describe('SessionPersistenceJsonl: edge cases', () => {
     // `readFirstLine` accumulates chunks before `list()` parses it.
     const bucket = join(root, '_no-cwd')
     await mkdir(bucket, { recursive: true })
-    const bigHeader = JSON.stringify({ type: 'session', version: 0, id: 'big', createdAt: 1, pad: 'x'.repeat(9000) })
+    const bigHeader = JSON.stringify({ type: 'session', version: 0, id: 'big', createdAt: 1, delegationDepth: 0, pad: 'x'.repeat(9000) })
     await writeFile(join(bucket, 'big.jsonl'), bigHeader + '\n')
     const ids = (await ctx.sessionPersistence.list()).map(x => x.id)
     expect(ids).toContain('big')
diff --git a/packages/session-persistence/session-persistence-sqlite/src/index.ts b/packages/session-persistence/session-persistence-sqlite/src/index.ts
index 4661b41309..edba26d9ae 100644
--- a/packages/session-persistence/session-persistence-sqlite/src/index.ts
+++ b/packages/session-persistence/session-persistence-sqlite/src/index.ts
@@ -253,14 +253,15 @@ export class SessionPersistenceSqlite extends SessionPersistence implements Pers
    */
   private writeRow(meta: SessionHeader): void {
     this.db.prepare(`
-      INSERT INTO sessions (id, version, created_at, cwd, parent_session, seed_length)
-      VALUES (?, ?, ?, ?, ?, ?)
+      INSERT INTO sessions (id, version, created_at, cwd, parent_session, seed_length, delegation_depth)
+      VALUES (?, ?, ?, ?, ?, ?, ?)
       ON CONFLICT(id) DO UPDATE SET
         version = excluded.version,
         created_at = excluded.created_at,
         cwd = excluded.cwd,
         parent_session = excluded.parent_session,
-        seed_length = excluded.seed_length
+        seed_length = excluded.seed_length,
+        delegation_depth = excluded.delegation_depth
     `).run(
       meta.id,
       meta.version,
@@ -268,6 +269,7 @@ export class SessionPersistenceSqlite extends SessionPersistence implements Pers
       meta.cwd ?? null,
       meta.parentSession ?? null,
       meta.seedLength ?? null,
+      meta.delegationDepth ?? null,
     )
   }
 }
diff --git a/packages/session-persistence/session-persistence-sqlite/src/schema.ts b/packages/session-persistence/session-persistence-sqlite/src/schema.ts
index adb23cbb43..4a7f12e759 100644
--- a/packages/session-persistence/session-persistence-sqlite/src/schema.ts
+++ b/packages/session-persistence/session-persistence-sqlite/src/schema.ts
@@ -15,7 +15,7 @@ import type { SessionEvent, SessionId, SessionHeader, SurfaceOp } from '@deepsee
  * layout; orthogonal to a session's own `version` (which versions the EVENT
  * vocabulary, stored per session in the `sessions` row).
  */
-export const SCHEMA_VERSION = 4
+export const SCHEMA_VERSION = 5
 
 /**
  * A row of the `sessions` table — the out-of-log metadata ({@link SessionHeader}).
@@ -31,6 +31,7 @@ export interface SessionRow {
   cwd: string | null
   parent_session: string | null
   seed_length: number | null
+  delegation_depth: number | null
 }
 
 /** An `events` table row: one `SessionEvent` mapped 1:1 (`data` is JSON text). */
@@ -83,9 +84,10 @@ export function openDatabase(path: string, journalMode: JournalMode): DatabaseSy
       id             TEXT PRIMARY KEY,
       version        INTEGER NOT NULL,
       created_at     INTEGER NOT NULL,
-      cwd            TEXT,
-      parent_session TEXT,
-      seed_length    INTEGER
+      cwd              TEXT,
+      parent_session   TEXT,
+      seed_length      INTEGER,
+      delegation_depth INTEGER
     ) STRICT
   `)
   db.exec(`
@@ -116,6 +118,7 @@ export function rowToMeta(row: SessionRow): SessionHeader {
     ...row.cwd !== null ? { cwd: row.cwd } : {},
     ...row.parent_session !== null ? { parentSession: row.parent_session as SessionId } : {},
     ...row.seed_length !== null ? { seedLength: row.seed_length } : {},
+    ...row.delegation_depth !== null ? { delegationDepth: row.delegation_depth } : {},
   }
 }
 
diff --git a/packages/session-persistence/session-persistence-sqlite/tests/sqlite.spec.ts b/packages/session-persistence/session-persistence-sqlite/tests/sqlite.spec.ts
index f26edfa54d..83d16b3315 100644
--- a/packages/session-persistence/session-persistence-sqlite/tests/sqlite.spec.ts
+++ b/packages/session-persistence/session-persistence-sqlite/tests/sqlite.spec.ts
@@ -385,7 +385,7 @@ describe('SessionPersistenceSqlite: durability and crash semantics', () => {
   })
 
   it('exposes the schema version constant', () => {
-    expect(SCHEMA_VERSION).toBe(4)
+    expect(SCHEMA_VERSION).toBe(5)
   })
 })
 
diff --git a/packages/session-persistence/session-persistence/README.md b/packages/session-persistence/session-persistence/README.md
index ca04cd1ab8..6d9e1392fe 100644
--- a/packages/session-persistence/session-persistence/README.md
+++ b/packages/session-persistence/session-persistence/README.md
@@ -2,7 +2,7 @@
 
 The abstract durable session-persistence seam (`ctx.sessionPersistence`). Defines WHAT a persistence backend does — durably store, reload, and list sessions — without saying HOW. Mirrors the `dsh-bash` capability-seam template ([capability seams](../../../.agents/notes/implemented/architecture/2026-06-13-capability-seams.md)): an abstract service here, a concrete implementation in a sibling package, consumers that inject the interface.
 
-The persisted unit IS the existing `SessionEvent` (event-sourced model — the log is the single source of truth), so there is no parallel "persisted message" type. Metadata that is NOT replayable conversation state (format version, cwd, lineage, seed boundary) travels separately as `SessionHeader`, owned by `dsh-session` and re-exported here.
+The persisted unit IS the existing `SessionEvent` (event-sourced model — the log is the single source of truth), so there is no parallel "persisted message" type. Metadata that is NOT replayable conversation state (format version, cwd, lineage, seed boundary, delegation depth) travels separately as `SessionHeader`, owned by `dsh-session` and re-exported here.
 
 ## Service API (`ctx.sessionPersistence`)
 
@@ -51,7 +51,7 @@ Three backends run these suites: an in-memory reference (in `tests/`), `dsh-sess
 
 ## Metadata and location types
 
-Re-exported from `dsh-session`: `SessionHeader` (immutable session metadata: `version`, `id`, `createdAt`, `cwd?`, `parentSession?`, `seedLength?`). `SessionLocation` is `{ readonly kind: string; readonly path: string }`; its path is an absolute backend target, not proof that the artifact exists or contains an unflushed turn.
+Re-exported from `dsh-session`: `SessionHeader` (immutable session metadata: `version`, `id`, `createdAt`, `cwd?`, `parentSession?`, `seedLength?`, `delegationDepth?`). `SessionLocation` is `{ readonly kind: string; readonly path: string }`; its path is an absolute backend target, not proof that the artifact exists or contains an unflushed turn.
 
 ## Model Experience
 
diff --git a/packages/session-persistence/session-persistence/tests/coordinator-contract.ts b/packages/session-persistence/session-persistence/tests/coordinator-contract.ts
index defcaefb6d..5ef2ce2fad 100644
--- a/packages/session-persistence/session-persistence/tests/coordinator-contract.ts
+++ b/packages/session-persistence/session-persistence/tests/coordinator-contract.ts
@@ -106,6 +106,27 @@ export function runCoordinatorContract(name: string, makeFixture: () => Promise<
       }
     })
 
+    it('round-trips the delegation depth through persistence', async () => {
+      // A subagent child's recursion budget lives in its header; a reload that
+      // dropped it would reset the child to top-level and un-bound maxDepth
+      // (JSONL stores it in the header line; SQLite uses `delegation_depth`).
+      const fix = await makeFixture()
+      const { ctx, fiber } = await freshCtx(fix)
+      try {
+        const session = ctx.sessions.create(SessionId('delegated-child'), {
+          meta: { cwd: WORK, parentSession: SessionId('root'), delegationDepth: 2 },
+        })
+        send(session, oneTurnLog())
+        await ctx.parallel('session/flush', session)
+
+        const loaded = await ctx.sessionPersistence.load(SessionId('delegated-child'))
+        expect(loaded.meta.delegationDepth).toBe(2)
+      } finally {
+        await fiber.dispose()
+        await fix.cleanup()
+      }
+    })
+
     it('source-frozen events cannot be mutated after buffering and persist unchanged', async () => {
       const fix = await makeFixture()
       const { ctx, fiber } = await freshCtx(fix)
diff --git a/packages/subagent/subagent-inprocess/README.md b/packages/subagent/subagent-inprocess/README.md
index 0503db9dc4..d51fc53e5d 100644
--- a/packages/subagent/subagent-inprocess/README.md
+++ b/packages/subagent/subagent-inprocess/README.md
@@ -8,7 +8,7 @@ This package is the shared run driver for the two in-process providers. Spawn pa
 
 The driver follows this sequence:
 
-1. Validate the parent depth and optional absolute `maxDepth`, then derive child depth as parent depth plus one.
+1. Validate the parent depth and optional absolute `maxDepth`, then derive child depth as parent depth plus one and persist it in the child session header.
 2. Call `parent.ctx.agents.create` directly, passing the required request signal into the factory's creation transaction.
 3. During that transaction's unpublished setup window, install the requested persona, tool restriction, and structured-output runtime.
 4. Publish the child, retain the returned `AgentHandle`, and drive one task with `child.send(prompt)` followed by `child.whenIdle()`.
@@ -26,7 +26,7 @@ After fulfillment, the caller owns the run. Provider-plugin unload does not revo
 
 `InProcessRunOptions` is `{ seed?: SessionEvent[] }`. Spawn omits it. Fork supplies a balanced completed-turn prefix and records its length so the result reader never mistakes a seeded parent message for child output.
 
-Depth enforcement is internal to `startInProcessRun`: it reads `AgentOptions.subagentDepth`, treats absence as top-level depth zero, rejects malformed stored values, and reports an attempted child depth above `maxDepth`. An unrepresentable depth above the safe-integer domain is a `RangeError`.
+Depth enforcement is internal to `startInProcessRun`: it reads the parent depth via `delegationDepthOf` (the persisted `SessionHeader.delegationDepth` is authoritative; runtime `AgentOptions.subagentDepth` may deepen but never lower it, so a resumed child keeps its budget), treats absence as top-level depth zero, rejects malformed stored values, and reports an attempted child depth above `maxDepth`. An unrepresentable depth above the safe-integer domain is a `RangeError`. The child depth is written to the child header, so it survives persistence and resume.
 
 ## Structured output
 
diff --git a/packages/subagent/subagent-inprocess/src/index.ts b/packages/subagent/subagent-inprocess/src/index.ts
index 6e62ee5127..f0e9731c9d 100644
--- a/packages/subagent/subagent-inprocess/src/index.ts
+++ b/packages/subagent/subagent-inprocess/src/index.ts
@@ -12,7 +12,7 @@ import type { Context } from 'cordis'
 import type { Agent, AgentOptions } from '@deepseek-ai/dsh-agent'
 import { SessionId, type SessionEvent, type TurnEndReason } from '@deepseek-ai/dsh-session'
 import type { ContentBlock } from '@deepseek-ai/dsh-llm'
-import { assertSubagentMaxDepth } from '@deepseek-ai/dsh-subagent'
+import { assertSubagentMaxDepth, delegationDepthOf } from '@deepseek-ai/dsh-subagent'
 import type { SubagentResult, SubagentRun, SubagentStartRequest, SubagentStopReason } from '@deepseek-ai/dsh-subagent'
 import {
   attachStructuredRuntime,
@@ -24,27 +24,6 @@ export {
   STRUCTURED_OUTPUT_INSTRUCTION,
 } from './structured.ts'
 
-declare module '@deepseek-ai/dsh-agent' {
-  interface AgentOptions {
-    /** Delegation depth: zero for a top-level agent and parent depth + 1 for a child. */
-    subagentDepth?: number
-  }
-}
-
-/**
- * Read an agent's delegation depth, treating absence as top-level depth zero.
- * @param agent - the agent whose options carry the depth.
- * @returns its non-negative safe-integer depth.
- */
-function depthOf(agent: Agent): number {
-  const depth = agent.options.subagentDepth
-  if (depth === undefined) return 0
-  if (!Number.isSafeInteger(depth) || depth < 0 || Object.is(depth, -0)) {
-    throw new TypeError('agent subagentDepth must be a non-negative safe integer')
-  }
-  return depth
-}
-
 /** Thrown when starting a child would exceed the requested depth cap. */
 class SubagentDepthError extends Error {
   constructor(public readonly attemptedDepth: number, public readonly maxDepth: number) {
@@ -96,7 +75,7 @@ export async function startInProcessRun(
   assertSubagentMaxDepth(request.maxDepth)
   if (request.signal.aborted) throw prePublicationAbort()
   const parent = request.parent
-  const childDepth = depthOf(parent) + 1
+  const childDepth = delegationDepthOf(parent) + 1
   if (!Number.isSafeInteger(childDepth)) {
     throw new RangeError('subagent child depth exceeds the safe-integer range')
   }
@@ -133,6 +112,8 @@ export async function startInProcessRun(
     meta: {
       ...parentHeader.cwd !== undefined ? { cwd: parentHeader.cwd } : {},
       parentSession: parentHeader.id,
+      // Durable: the recursion budget must survive persistence and resume.
+      delegationDepth: childDepth,
       ...seedLength > 0 ? { seedLength } : {},
     },
     ...options.seed !== undefined ? { seed: options.seed } : {},
diff --git a/packages/subagent/subagent-inprocess/tests/subagent-inprocess.spec.ts b/packages/subagent/subagent-inprocess/tests/subagent-inprocess.spec.ts
index 13029ef3e7..e82c1ad028 100644
--- a/packages/subagent/subagent-inprocess/tests/subagent-inprocess.spec.ts
+++ b/packages/subagent/subagent-inprocess/tests/subagent-inprocess.spec.ts
@@ -58,6 +58,43 @@ describe('startInProcessRun', () => {
     await run.dispose()
   })
 
+  it('persists the child depth in its session header', async () => {
+    const { ctx, parent } = await setup([textResponse('child answer')])
+    const run = await startInProcessRun(request(parent), {})
+    await run.result
+    // The recursion budget is durable session data, not only runtime options —
+    // a depth that lived only in AgentOptions would reset to 0 on resume.
+    expect(ctx.agents.get(run.id)!.session.header.delegationDepth).toBe(1)
+    await run.dispose()
+  })
+
+  it('counts a RESUMED child by its persisted header depth, not the absent runtime depth', async () => {
+    // Resume rebuilds runtime options, so the durable header must keep this
+    // depth-1 child from delegating as though it were top-level.
+    const { ctx } = await setup([textResponse('unused')])
+    const resumed = (await ctx.agents.create({
+      sessionId: SessionId('resumed-child'),
+      meta: { parentSession: SessionId('root'), delegationDepth: 1 },
+      agentOptions: { provider: 'mock', model: 'mock' },
+      signal: new AbortController().signal,
+    })).agent
+    await expect(startInProcessRun({ ...request(resumed), maxDepth: 1 }, {}))
+      .rejects.toMatchObject({ name: 'SubagentDepthError', attemptedDepth: 2, maxDepth: 1 })
+  })
+
+  it('lets runtime options deepen but never lower the persisted depth', async () => {
+    const { ctx } = await setup([textResponse('unused')])
+    const parent = (await ctx.agents.create({
+      sessionId: SessionId('deep-parent'),
+      meta: { delegationDepth: 2 },
+      agentOptions: { provider: 'mock', model: 'mock', subagentDepth: 1 },
+      signal: new AbortController().signal,
+    })).agent
+    // Persisted 2 vs runtime 1: the child is depth 3, so maxDepth 2 rejects.
+    await expect(startInProcessRun({ ...request(parent), maxDepth: 2 }, {}))
+      .rejects.toMatchObject({ name: 'SubagentDepthError', attemptedDepth: 3, maxDepth: 2 })
+  })
+
   it('rejects invalid and exceeded depth before publication', async () => {
     const { parent } = await setup([])
     await expect(startInProcessRun({ ...request(parent), maxDepth: -1 }, {}))
@@ -65,11 +102,11 @@ describe('startInProcessRun', () => {
     await expect(startInProcessRun({ ...request(parent), maxDepth: 0 }, {}))
       .rejects.toMatchObject({ name: 'SubagentDepthError' })
     for (const value of [Number.NaN, 1.5, -1, -0, Number.MAX_SAFE_INTEGER + 1]) {
-      const malformed = { options: { subagentDepth: value } } as unknown as Agent
+      const malformed = { options: { subagentDepth: value }, session: { header: {} } } as unknown as Agent
       await expect(startInProcessRun(request(malformed), {}))
         .rejects.toThrow('agent subagentDepth must be a non-negative safe integer')
     }
-    const maxParent = { options: { subagentDepth: Number.MAX_SAFE_INTEGER } } as unknown as Agent
+    const maxParent = { options: { subagentDepth: Number.MAX_SAFE_INTEGER }, session: { header: {} } } as unknown as Agent
     await expect(startInProcessRun(request(maxParent), {})).rejects.toBeInstanceOf(RangeError)
   })
 
diff --git a/packages/subagent/subagent/README.md b/packages/subagent/subagent/README.md
index 5097ad914a..105af77450 100644
--- a/packages/subagent/subagent/README.md
+++ b/packages/subagent/subagent/README.md
@@ -40,6 +40,10 @@ Start-time features are advertised in `provider.capabilities` because the servic
 - `toolFilter` — apply the requested child tool restriction.
 - `persona` — apply a per-child persona.
 
+## Delegation depth
+
+The seam owns the depth vocabulary shared by implementations and consumers: the `AgentOptions.subagentDepth` declaration, `assertSubagentMaxDepth`, and `delegationDepthOf(agent)`. The persisted `SessionHeader.delegationDepth` is authoritative and monotone — runtime options may deepen the count but never lower it, so a resumed child cannot be re-counted as top-level.
+
 Runtime features are optional methods on `SubagentRun`: `sendMessage?` steers a live child, while `resume?` asynchronously creates a continuation run. Method presence is the capability check.
 
 `inheritsParentContext` is descriptive rather than enforceable. It says only whether the child sees completed parent conversation history (`fork` does; `spawn` and ACP do not), not whether it inherits tools, services, or authority.
diff --git a/packages/subagent/subagent/src/index.ts b/packages/subagent/subagent/src/index.ts
index 19779f9137..00655f1f51 100644
--- a/packages/subagent/subagent/src/index.ts
+++ b/packages/subagent/subagent/src/index.ts
@@ -57,6 +57,33 @@ export type {
   SubagentStopReasonMap,
 } from './types.ts'
 
+declare module '@deepseek-ai/dsh-agent' {
+  interface AgentOptions {
+    /** Delegation depth: zero for a top-level agent and parent depth + 1 for a child. */
+    subagentDepth?: number
+  }
+}
+
+/**
+ * Read an agent's delegation depth, treating absence as top-level depth zero.
+ * The persisted session header is authoritative and monotone: runtime
+ * `AgentOptions.subagentDepth` may DEEPEN the count but can never lower it —
+ * a resumed child arrives with fresh options, and counting it from zero would
+ * let it delegate as if it were top-level.
+ * @param agent - the agent whose header and options carry the depth.
+ * @returns its non-negative safe-integer depth.
+ * @throws if the runtime `AgentOptions.subagentDepth` is not a non-negative safe integer.
+ */
+export function delegationDepthOf(agent: Agent): number {
+  const runtime = agent.options.subagentDepth
+  if (runtime !== undefined && (!Number.isSafeInteger(runtime) || runtime < 0 || Object.is(runtime, -0))) {
+    throw new TypeError('agent subagentDepth must be a non-negative safe integer')
+  }
+  // The header value was validated at the session boundary (creation and
+  // persistence load both construct through the store).
+  return Math.max(agent.session.header.delegationDepth ?? 0, runtime ?? 0)
+}
+
 /**
  * Reject a recursion cap that cannot represent an exact delegation depth.
  * @param maxDepth - the optional runtime value to validate.
diff --git a/packages/subagent/tool-subagent/README.md b/packages/subagent/tool-subagent/README.md
index 6355208a4d..e2af5ac552 100644
--- a/packages/subagent/tool-subagent/README.md
+++ b/packages/subagent/tool-subagent/README.md
@@ -22,7 +22,7 @@ With `run_in_background: true`, the tool registers the parent-owned task before
 | `agentOptions` | Default child options, currently including `model`. |
 | `persona` | Per-child persona; requires provider `persona` capability. |
 | `toolFilter` | Per-child global-tool restriction; requires `toolFilter` capability. |
-| `maxDepth` | Absolute delegation-depth cap; requires `depthLimit` capability. |
+| `maxDepth` | Absolute delegation-depth cap, default `3` (`0` forbids delegation); a numeric cap requires the `depthLimit` capability and fails the mount without it. `'provider-managed'` sends no cap for an out-of-process provider whose budget belongs to the child harness. The tool stays visible at the cap; each attempted start checks the calling agent's current depth and returns an errored tool result when rejected. |
 
 ## Concurrency
 
diff --git a/packages/subagent/tool-subagent/src/index.ts b/packages/subagent/tool-subagent/src/index.ts
index f46f3dda2c..bcd28c6ab1 100644
--- a/packages/subagent/tool-subagent/src/index.ts
+++ b/packages/subagent/tool-subagent/src/index.ts
@@ -45,8 +45,7 @@ export interface Config {
   /**
    * Tool filter applied to every child. Filtered tools disappear from its
    * prompt and reject execution. Requires the provider's `toolFilter`
-   * capability; unknown names fail startup. Children otherwise see this tool,
-   * so deny it or set `maxDepth` to bound recursion.
+   * capability; unknown names fail startup.
    */
   toolFilter?: {
     /** Global tool names the child keeps; everything else is removed. */
@@ -55,10 +54,15 @@ export interface Config {
     deny?: string[]
   }
   /**
-   * Maximum child depth. Requires the provider's `depthLimit` capability and a
-   * non-negative safe integer. Omission is unbounded.
+   * Maximum child depth: a non-negative safe integer (default `3`; `0` forbids
+   * delegation entirely), or `'provider-managed'` to send no cap. A numeric cap
+   * requires the provider's `depthLimit` capability (mount fails loud
+   * otherwise). The provider checks the calling agent's current depth at every
+   * start; the tool remains model-visible so runtime policy owns rejection.
+   * `'provider-managed'` is for an out-of-process provider (ACP) whose
+   * recursion budget belongs to the child harness's own deployment.
    */
-  maxDepth?: number
+  maxDepth?: number | 'provider-managed'
 }
 
 export const Config: z<Config> = z.object({
@@ -76,7 +80,7 @@ export const Config: z<Config> = z.object({
     allow: z.array(z.string()).default(undefined as unknown as string[]),
     deny: z.array(z.string()).default(undefined as unknown as string[]),
   }).default(undefined as unknown as { allow: string[]; deny: string[] }),
-  maxDepth: z.natural().max(Number.MAX_SAFE_INTEGER),
+  maxDepth: z.union([z.natural().max(Number.MAX_SAFE_INTEGER), z.const('provider-managed' as const)]).default(3),
 })
 
 /**
@@ -195,6 +199,7 @@ function providerWording(inheritsConversation: boolean): { description: string;
 }
 
 function startRequest(config: Config, prompt: string, parent: Agent, signal: AbortSignal): SubagentStartRequest {
+  const maxDepth = typeof config.maxDepth === 'number' ? config.maxDepth : undefined
   return {
     prompt: [{ type: 'text', text: prompt }],
     parent,
@@ -202,7 +207,7 @@ function startRequest(config: Config, prompt: string, parent: Agent, signal: Abo
     ...config.agentOptions !== undefined ? { agentOptions: config.agentOptions } : {},
     ...config.persona !== undefined ? { persona: config.persona } : {},
     ...config.toolFilter !== undefined ? { toolFilter: config.toolFilter } : {},
-    ...config.maxDepth !== undefined ? { maxDepth: config.maxDepth } : {},
+    ...maxDepth !== undefined ? { maxDepth } : {},
   }
 }
 
@@ -218,8 +223,9 @@ async function settleStart(start: Promise<SubagentRun>, signal: AbortSignal): Pr
 }
 
 export function apply(ctx: Context, config: Config): void {
-  // Direct apply() bypasses Schemastery's numeric constraints.
-  assertSubagentMaxDepth(config.maxDepth)
+  // Direct apply() bypasses Schemastery's numeric constraints. A direct-apply
+  // omission stays capless (the schema default only runs through the loader).
+  if (config.maxDepth !== 'provider-managed') assertSubagentMaxDepth(config.maxDepth)
   // Reject an empty explicit filter at load instead of failing every delegation.
   if (config.toolFilter !== undefined && config.toolFilter.allow === undefined && config.toolFilter.deny === undefined) {
     throw new Error('tool-subagent: `toolFilter` is configured but names neither `allow` nor `deny` — remove the key or fill the filter')
@@ -228,6 +234,15 @@ export function apply(ctx: Context, config: Config): void {
   // can change provider availability while this fiber remains active.
   let disposeTool: (() => void) | undefined
   const mount = (provider: SubagentProvider): void => {
+    // A numeric cap the provider cannot enforce is a misconfiguration — fail at
+    // mount (the earliest point the provider's capabilities are known), not on
+    // the first delegation.
+    if (typeof config.maxDepth === 'number' && !provider.capabilities.depthLimit) {
+      throw new Error(
+        `tool-subagent: provider "${provider.name}" cannot enforce maxDepth (no depthLimit capability) — `
+        + 'set maxDepth: \'provider-managed\' to leave the recursion budget to the provider',
+      )
+    }
     const wording = providerWording(provider.inheritsParentContext)
     const backgroundEnabled = config.enableRunInBackground !== false
     disposeTool = ctx.tools.register(defineTool({
diff --git a/packages/subagent/tool-subagent/tests/tool-subagent.spec.ts b/packages/subagent/tool-subagent/tests/tool-subagent.spec.ts
index d88367ced5..9e4d68c08c 100644
--- a/packages/subagent/tool-subagent/tests/tool-subagent.spec.ts
+++ b/packages/subagent/tool-subagent/tests/tool-subagent.spec.ts
@@ -7,6 +7,7 @@ import ToolRegistry from '@deepseek-ai/dsh-tools'
 import { type Agent } from '@deepseek-ai/dsh-agent'
 import AgentRegistry from '@deepseek-ai/dsh-agent'
 import SubagentService from '@deepseek-ai/dsh-subagent'
+import type { SubagentStartRequest } from '@deepseek-ai/dsh-subagent'
 import TaskService from '@deepseek-ai/dsh-tasks'
 import * as ToolTasks from '@deepseek-ai/dsh-tool-tasks'
 import * as mock from './scripted-provider.ts'
@@ -22,7 +23,7 @@ import { SessionId } from '@deepseek-ai/dsh-session'
  * shipping code path.
  */
 
-/** A minimal parent Agent — the tool reads `agent.id` for `parent`. */
+/** A minimal parent Agent passed through to the provider request. */
 function fakeAgent(id = 'parent-1'): Agent {
   return { id: SessionId(id) } as unknown as Agent
 }
@@ -85,7 +86,7 @@ describe('dsh-tool-subagent', () => {
     // Schema omission is advertising, not enforcement: the arg validator
     // allows undeclared keys, so the opt-out must also hold in execute().
     const ctx = await setup({ provider: 'mock', enableRunInBackground: false })
-    const parent = { id: SessionId('sess-off'), inject: () => {}, session: { header: { version: 0, id: 'sess-off', createdAt: 0 } } } as unknown as Agent
+    const parent = { id: SessionId('sess-off'), inject: () => {}, options: {}, session: { header: { version: 0, id: 'sess-off', createdAt: 0 } } } as unknown as Agent
 
     const forced = await callSubagent(ctx, { description: 'd', prompt: 'p', run_in_background: true }, { agent: parent })
     expect(forced.isError).toBe(true)
@@ -162,7 +163,7 @@ describe('dsh-tool-subagent', () => {
         dispose: async () => {},
       }),
     })
-    await ctx.plugin(tool, { provider: 'weird' })
+    await ctx.plugin(tool, { provider: 'weird', maxDepth: 'provider-managed' })
 
     const result = await callSubagent(ctx, { description: 'd', prompt: 'p' })
     expect(result.isError).toBe(true)
@@ -191,7 +192,7 @@ describe('dsh-tool-subagent', () => {
         }
       },
     })
-    await ctx.plugin(tool, { provider: 'capture', agentOptions: { model: 'child-model' } })
+    await ctx.plugin(tool, { provider: 'capture', agentOptions: { model: 'child-model' }, maxDepth: 'provider-managed' })
 
     await callSubagent(ctx, { description: 'd', prompt: 'p' })
     expect(seen?.agentOptions).toEqual({ model: 'child-model' })
@@ -348,7 +349,7 @@ describe('dsh-tool-subagent', () => {
         dispose: async () => void disposed(),
       }),
     })
-    await ctx.plugin(tool, { provider: 'spy' })
+    await ctx.plugin(tool, { provider: 'spy', maxDepth: 'provider-managed' })
 
     await callSubagent(ctx, { description: 'd', prompt: 'p' })
     expect(disposed).toHaveBeenCalledTimes(1)
@@ -371,7 +372,7 @@ describe('dsh-tool-subagent', () => {
         dispose: async () => void disposed(),
       }),
     })
-    await ctx.plugin(tool, { provider: 'spy' })
+    await ctx.plugin(tool, { provider: 'spy', maxDepth: 'provider-managed' })
 
     const result = await callSubagent(ctx, { description: 'd', prompt: 'p' })
     expect(result.isError).toBe(true)
@@ -404,7 +405,7 @@ describe('dsh-tool-subagent', () => {
         }
       },
     })
-    await ctx.plugin(tool, { provider: 'spy' })
+    await ctx.plugin(tool, { provider: 'spy', maxDepth: 'provider-managed' })
 
     const controller = new AbortController()
     const pending = callSubagent(ctx, { description: 'd', prompt: 'p' }, { signal: controller.signal })
@@ -432,7 +433,7 @@ describe('dsh-tool-subagent', () => {
         throw new Error('start aborted')
       },
     })
-    await ctx.plugin(tool, { provider: 'spy' })
+    await ctx.plugin(tool, { provider: 'spy', maxDepth: 'provider-managed' })
 
     const controller = new AbortController()
     controller.abort() // already aborted BEFORE the tool runs
@@ -511,7 +512,6 @@ describe('dsh-tool-subagent', () => {
   })
 
   it.each([
-    { label: 'null', value: null as unknown as number },
     { label: 'a string', value: '1' as unknown as number },
     { label: 'NaN', value: Number.NaN },
     { label: 'positive infinity', value: Number.POSITIVE_INFINITY },
@@ -555,7 +555,7 @@ describe('dsh-tool-subagent', () => {
         }
       },
     })
-    await ctx.plugin(tool, { provider: 'capture3', toolFilter: { deny: ['subagent'] } })
+    await ctx.plugin(tool, { provider: 'capture3', toolFilter: { deny: ['subagent'] }, maxDepth: 'provider-managed' })
     await callSubagent(ctx, { description: 'd', prompt: 'p' })
     expect(seen?.toolFilter).toEqual({ deny: ['subagent'] })
     expect(seen?.toolFilter).not.toHaveProperty('allow')
@@ -585,7 +585,7 @@ describe('dsh-tool-subagent', () => {
         }
       },
     })
-    await ctx.plugin(tool, { provider: 'capture4' })
+    await ctx.plugin(tool, { provider: 'capture4', maxDepth: 'provider-managed' })
     await callSubagent(ctx, { description: 'd', prompt: 'p' })
     expect(seen).toBeDefined()
     expect(seen).not.toHaveProperty('agentOptions')
@@ -616,6 +616,7 @@ describe('dsh-tool-subagent background mode', () => {
       id,
       ctx: scopeFiber.ctx,
       inject,
+      options: {},
       session: { id, header: { version: 0, id, createdAt: 0 } },
     } as unknown as Agent
     ctx.agents.register(agent)
@@ -846,6 +847,7 @@ describe('background preflight failure (no orphaned child, by construction)', ()
       id,
       ctx: scopeFiber.ctx,
       inject: () => {},
+      options: {},
       session: { id, header: { version: 0, id, createdAt: 0 } },
     } as unknown as Agent
     ctx.agents.register(parent)
@@ -879,3 +881,85 @@ describe('background preflight failure (no orphaned child, by construction)', ()
     expect(starts).toBe(0)
   })
 })
+
+describe('depth budget configuration', () => {
+  /** Mount the tool over a request-capturing provider with full capabilities. */
+  async function captureSetup(config: Omit<tool.Config, 'provider'> = {}) {
+    const requests: SubagentStartRequest[] = []
+    const ctx = new Context()
+    await ctx.plugin(SystemPrompt)
+    await ctx.plugin(ToolRegistry)
+    await ctx.plugin(SubagentService)
+    ctx.subagents.registerProvider({
+      name: 'capture',
+      capabilities: { outputSchema: true, depthLimit: true, toolFilter: true, persona: true },
+      inheritsParentContext: false,
+      start: async (request) => {
+        requests.push(request)
+        return {
+          id: SessionId(`capture-child-${requests.length}`),
+          localAgent: undefined,
+          result: Promise.resolve({ output: [{ type: 'text', text: 'ok' }], stopReason: 'completed' as const }),
+          dispose: async () => {},
+        }
+      },
+    })
+    await ctx.plugin(tool, { provider: 'capture', ...config })
+    return { ctx, requests }
+  }
+
+  it('defaults maxDepth to 3 and forwards it in the start request', async () => {
+    const { ctx, requests } = await captureSetup()
+    await callSubagent(ctx, { description: 'd', prompt: 'p' })
+    expect(requests[0]?.maxDepth).toBe(3)
+    expect(requests[0]?.toolFilter).toBeUndefined()
+  })
+
+  it('forwards an explicit tool filter unchanged instead of encoding the depth policy into it', async () => {
+    const { ctx, requests } = await captureSetup({ toolFilter: { deny: ['dangerous'] }, maxDepth: 0 })
+    await callSubagent(ctx, { description: 'd', prompt: 'p' })
+    expect(requests[0]?.maxDepth).toBe(0)
+    expect(requests[0]?.toolFilter).toEqual({ deny: ['dangerous'] })
+  })
+
+  it('rejects a numeric maxDepth on a provider without the depthLimit capability at mount', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SystemPrompt)
+    await ctx.plugin(ToolRegistry)
+    await ctx.plugin(SubagentService)
+    ctx.subagents.registerProvider({
+      name: 'no-depth',
+      capabilities: { outputSchema: false, depthLimit: false, toolFilter: false, persona: false },
+      inheritsParentContext: false,
+      start: async () => { throw new Error('unreachable') },
+    })
+    await expect(ctx.plugin(tool, { provider: 'no-depth' }))
+      .rejects.toThrow(/provider-managed/)
+  })
+
+  it("'provider-managed' omits the cap so a capability-less provider mounts and starts", async () => {
+    const requests: SubagentStartRequest[] = []
+    const ctx = new Context()
+    await ctx.plugin(SystemPrompt)
+    await ctx.plugin(ToolRegistry)
+    await ctx.plugin(SubagentService)
+    ctx.subagents.registerProvider({
+      name: 'external',
+      capabilities: { outputSchema: false, depthLimit: false, toolFilter: false, persona: false },
+      inheritsParentContext: false,
+      start: async (request) => {
+        requests.push(request)
+        return {
+          id: SessionId('external-child'),
+          localAgent: undefined,
+          result: Promise.resolve({ output: [{ type: 'text', text: 'ok' }], stopReason: 'completed' as const }),
+          dispose: async () => {},
+        }
+      },
+    })
+    await ctx.plugin(tool, { provider: 'external', maxDepth: 'provider-managed' })
+    await callSubagent(ctx, { description: 'd', prompt: 'p' })
+    expect(requests[0]?.maxDepth).toBeUndefined()
+    expect(requests[0]?.toolFilter).toBeUndefined()
+  })
+})
diff --git a/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-child/behavior.json b/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-child/behavior.json
index d44a3a9698..fd06978be1 100644
--- a/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-child/behavior.json
+++ b/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-child/behavior.json
@@ -2,11 +2,11 @@
   "prompt": "respond",
   "logs": [
     { "file": "b/parent.jsonl", "lines": [
-      { "type": "session", "id": "{{SID}}", "createdAt": 700, "cwd": "{{CWD}}" },
+      { "type": "session", "id": "{{SID}}", "createdAt": 700, "cwd": "{{CWD}}", "delegationDepth": 0 },
       { "type": "request/header", "seq": 0, "time": 3, "data": { "header": { "config": { "model": "fake" }, "system": "SYS PROMPT", "tools": [{ "name": "t1", "description": "D1", "parameters": { "type": "object" } }] }, "reason": "initial" } }
     ]},
     { "file": "b/child.jsonl", "lines": [
-      { "type": "session", "id": "abababab-cdcd-4efe-8ada-badabadabada", "createdAt": 800, "cwd": "{{CWD}}", "parentSession": "{{SID}}" },
+      { "type": "session", "id": "abababab-cdcd-4efe-8ada-badabadabada", "createdAt": 800, "cwd": "{{CWD}}", "parentSession": "{{SID}}", "delegationDepth": 1 },
       { "type": "request/header", "seq": 0, "time": 2, "data": { "header": { "config": { "model": "fake" }, "system": "SYS PROMPT", "tools": [{ "name": "t1", "description": "D1", "parameters": { "type": "object" } }] }, "reason": "initial" } }
     ]}
   ]
diff --git a/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-child/session.1.jsonl b/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-child/session.1.jsonl
index 1caf2610b3..4fa81014ae 100644
--- a/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-child/session.1.jsonl
+++ b/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-child/session.1.jsonl
@@ -1,2 +1,2 @@
-{"type":"session","id":"abababab-cdcd-4efe-8ada-badabadabada","createdAt":800,"cwd":"/var/folders/2g/b32ct0qn1d728l_v6tdkjytr0000gn/T/acp-snap-cwd-KBQJbW","parentSession":"f6fa7fcf-dd9c-4b39-8815-b25ddcebfd88"}
+{"type":"session","id":"abababab-cdcd-4efe-8ada-badabadabada","createdAt":800,"cwd":"/var/folders/2g/b32ct0qn1d728l_v6tdkjytr0000gn/T/acp-snap-cwd-KBQJbW","parentSession":"f6fa7fcf-dd9c-4b39-8815-b25ddcebfd88","delegationDepth":1}
 {"type":"request/header","seq":0,"time":2,"data":{"header":{"config":{"model":"fake"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
diff --git a/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-child/session.jsonl b/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-child/session.jsonl
index a2beac360d..e972a78d8e 100644
--- a/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-child/session.jsonl
+++ b/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-child/session.jsonl
@@ -1,2 +1,2 @@
-{"type":"session","id":"f6fa7fcf-dd9c-4b39-8815-b25ddcebfd88","createdAt":700,"cwd":"/var/folders/2g/b32ct0qn1d728l_v6tdkjytr0000gn/T/acp-snap-cwd-KBQJbW"}
+{"type":"session","id":"f6fa7fcf-dd9c-4b39-8815-b25ddcebfd88","createdAt":700,"cwd":"/var/folders/2g/b32ct0qn1d728l_v6tdkjytr0000gn/T/acp-snap-cwd-KBQJbW","delegationDepth":0}
 {"type":"request/header","seq":0,"time":3,"data":{"header":{"config":{"model":"fake"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
diff --git a/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-pin/behavior.json b/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-pin/behavior.json
index a24e30d80a..b0ed5f1a3f 100644
--- a/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-pin/behavior.json
+++ b/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-pin/behavior.json
@@ -3,7 +3,7 @@
   "logs": [{
     "file": "b/main.jsonl",
     "lines": [
-      { "type": "session", "id": "{{SID}}", "createdAt": 600, "cwd": "{{CWD}}" },
+      { "type": "session", "id": "{{SID}}", "createdAt": 600, "cwd": "{{CWD}}", "delegationDepth": 0 },
       { "type": "request/header", "seq": 0, "time": 4, "data": { "header": { "config": { "model": "fake" }, "system": "SYS PROMPT", "tools": [{ "name": "t1", "description": "D1", "parameters": { "type": "object" } }] }, "reason": "initial" } }
     ]
   }]
diff --git a/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-pin/session.jsonl b/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-pin/session.jsonl
index e9dd3fb16c..40bb4d37dc 100644
--- a/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-pin/session.jsonl
+++ b/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-pin/session.jsonl
@@ -1,2 +1,2 @@
-{"type":"session","id":"ccdc749f-56f3-4267-9750-598b5c60b7b2","createdAt":600,"cwd":"/var/folders/2g/b32ct0qn1d728l_v6tdkjytr0000gn/T/acp-snap-cwd-nOQ4Gy"}
+{"type":"session","id":"ccdc749f-56f3-4267-9750-598b5c60b7b2","createdAt":600,"cwd":"/var/folders/2g/b32ct0qn1d728l_v6tdkjytr0000gn/T/acp-snap-cwd-nOQ4Gy","delegationDepth":0}
 {"type":"request/header","seq":0,"time":4,"data":{"header":{"config":{"model":"fake"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
diff --git a/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-skip/session.jsonl b/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-skip/session.jsonl
index 104f2a0df2..035d1353b7 100644
--- a/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-skip/session.jsonl
+++ b/packages/support/acp-snapshot/tests/fixtures/record-suite/rec-skip/session.jsonl
@@ -1 +1 @@
-{"type":"session","id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}"}
+{"type":"session","id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0}
diff --git a/packages/support/acp-snapshot/tests/fixtures/suite/authored-error/behavior.json b/packages/support/acp-snapshot/tests/fixtures/suite/authored-error/behavior.json
index 808d9672b9..991de99fd6 100644
--- a/packages/support/acp-snapshot/tests/fixtures/suite/authored-error/behavior.json
+++ b/packages/support/acp-snapshot/tests/fixtures/suite/authored-error/behavior.json
@@ -3,7 +3,7 @@
   "logs": [{
     "file": "b/main.jsonl",
     "lines": [
-      { "type": "session", "id": "{{SID}}", "createdAt": 500, "cwd": "{{CWD}}" },
+      { "type": "session", "id": "{{SID}}", "createdAt": 500, "cwd": "{{CWD}}", "delegationDepth": 0 },
       { "type": "turn/end", "seq": 1, "time": 9, "data": { "error": "model exploded" } }
     ]
   }]
diff --git a/packages/support/acp-snapshot/tests/fixtures/suite/authored-error/session.jsonl b/packages/support/acp-snapshot/tests/fixtures/suite/authored-error/session.jsonl
index 36991a214e..a202c7141d 100644
--- a/packages/support/acp-snapshot/tests/fixtures/suite/authored-error/session.jsonl
+++ b/packages/support/acp-snapshot/tests/fixtures/suite/authored-error/session.jsonl
@@ -1,2 +1,2 @@
-{"type":"session","id":"44444444-3333-4222-8111-000000000000","createdAt":17,"cwd":"/rec/authored-cwd"}
+{"type":"session","id":"44444444-3333-4222-8111-000000000000","createdAt":17,"cwd":"/rec/authored-cwd","delegationDepth":0}
 {"type":"turn/end","seq":1,"time":17,"data":{"error":"model exploded"}}
diff --git a/packages/support/acp-snapshot/tests/fixtures/suite/blocked-log/behavior.json b/packages/support/acp-snapshot/tests/fixtures/suite/blocked-log/behavior.json
index e0a438297d..209159da7d 100644
--- a/packages/support/acp-snapshot/tests/fixtures/suite/blocked-log/behavior.json
+++ b/packages/support/acp-snapshot/tests/fixtures/suite/blocked-log/behavior.json
@@ -3,7 +3,7 @@
   "logs": [{
     "file": "b/main.jsonl",
     "lines": [
-      { "type": "session", "id": "{{SID}}", "createdAt": 400, "cwd": "{{CWD}}" },
+      { "type": "session", "id": "{{SID}}", "createdAt": 400, "cwd": "{{CWD}}", "delegationDepth": 0 },
       { "type": "hook/result", "seq": 1, "time": 8, "data": { "decision": "block", "durationMs": 37 } }
     ]
   }]
diff --git a/packages/support/acp-snapshot/tests/fixtures/suite/blocked-log/session.jsonl b/packages/support/acp-snapshot/tests/fixtures/suite/blocked-log/session.jsonl
index 6d8474812d..75eb18fa71 100644
--- a/packages/support/acp-snapshot/tests/fixtures/suite/blocked-log/session.jsonl
+++ b/packages/support/acp-snapshot/tests/fixtures/suite/blocked-log/session.jsonl
@@ -1,2 +1,2 @@
-{"type":"session","id":"99999999-8888-4777-8666-555555555555","createdAt":13,"cwd":"/rec/blocked-cwd"}
+{"type":"session","id":"99999999-8888-4777-8666-555555555555","createdAt":13,"cwd":"/rec/blocked-cwd","delegationDepth":0}
 {"type":"hook/result","seq":1,"time":13,"data":{"decision":"block","durationMs":99}}
diff --git a/packages/support/acp-snapshot/tests/fixtures/suite/no-model/session.jsonl b/packages/support/acp-snapshot/tests/fixtures/suite/no-model/session.jsonl
index 104f2a0df2..035d1353b7 100644
--- a/packages/support/acp-snapshot/tests/fixtures/suite/no-model/session.jsonl
+++ b/packages/support/acp-snapshot/tests/fixtures/suite/no-model/session.jsonl
@@ -1 +1 @@
-{"type":"session","id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}"}
+{"type":"session","id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0}
diff --git a/packages/support/acp-snapshot/tests/fixtures/suite/pin-turn/behavior.json b/packages/support/acp-snapshot/tests/fixtures/suite/pin-turn/behavior.json
index 4b63893a62..ad4c368e49 100644
--- a/packages/support/acp-snapshot/tests/fixtures/suite/pin-turn/behavior.json
+++ b/packages/support/acp-snapshot/tests/fixtures/suite/pin-turn/behavior.json
@@ -3,7 +3,7 @@
   "logs": [{
     "file": "b/main.jsonl",
     "lines": [
-      { "type": "session", "id": "{{SID}}", "createdAt": 100, "cwd": "{{CWD}}" },
+      { "type": "session", "id": "{{SID}}", "createdAt": 100, "cwd": "{{CWD}}", "delegationDepth": 0 },
       { "type": "request/header", "seq": 0, "time": 100, "data": { "header": { "config": { "model": "fake" }, "system": "SYS PROMPT", "tools": [{ "name": "t1", "description": "D1", "parameters": { "type": "object" } }] }, "reason": "initial" } },
       { "type": "request/header", "seq": 1, "time": 100, "data": { "header": { "config": { "model": "fake" }, "system": "SYS PROMPT\n\nNEW PROMPT LINE", "tools": [{ "name": "t1", "description": "D1", "parameters": { "type": "object" } }] }, "reason": "change" } },
       { "type": "turn/start", "seq": 2, "time": 100, "data": { "turn": 1 } }
diff --git a/packages/support/acp-snapshot/tests/fixtures/suite/pin-turn/session.jsonl b/packages/support/acp-snapshot/tests/fixtures/suite/pin-turn/session.jsonl
index 54b64b59a3..693e728d2c 100644
--- a/packages/support/acp-snapshot/tests/fixtures/suite/pin-turn/session.jsonl
+++ b/packages/support/acp-snapshot/tests/fixtures/suite/pin-turn/session.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","id":"12121212-3434-4545-8686-787878787878","createdAt":7,"cwd":"/rec/pin-cwd"}
+{"type":"session","id":"12121212-3434-4545-8686-787878787878","createdAt":7,"cwd":"/rec/pin-cwd","delegationDepth":0}
 {"type":"request/header","seq":0,"time":7,"data":{"header":{"config":{"model":"fake"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
 {"type":"request/header","seq":1,"time":7,"data":{"header":{"config":{"model":"fake"},"system":"{{system}}","tools":"{{tools}}"},"reason":"change"}}
 {"type":"turn/start","seq":2,"time":7,"data":{"turn":1}}
diff --git a/packages/support/acp-snapshot/tests/fixtures/suite/plain-turn/behavior.json b/packages/support/acp-snapshot/tests/fixtures/suite/plain-turn/behavior.json
index d5cbbf9d28..8903d0360e 100644
--- a/packages/support/acp-snapshot/tests/fixtures/suite/plain-turn/behavior.json
+++ b/packages/support/acp-snapshot/tests/fixtures/suite/plain-turn/behavior.json
@@ -3,12 +3,12 @@
   "echoWorkspace": true,
   "logs": [
     { "file": "b/parent.jsonl", "lines": [
-      { "type": "session", "id": "{{SID}}", "createdAt": 200, "cwd": "{{CWD}}" },
+      { "type": "session", "id": "{{SID}}", "createdAt": 200, "cwd": "{{CWD}}", "delegationDepth": 0 },
       { "type": "request/header", "seq": 0, "time": 5, "data": { "header": { "config": { "model": "fake" }, "system": "SYS PROMPT", "tools": [{ "name": "t1", "description": "D1", "parameters": { "type": "object" } }] }, "reason": "initial" } },
       { "type": "assistant/chunk", "seq": 1, "time": 5, "data": { "turn": 1, "step": 1, "chunk": { "type": "text-delta", "index": 0, "text": "hi" } } }
     ]},
     { "file": "b/child.jsonl", "lines": [
-      { "type": "session", "id": "eeeeeeee-1111-4222-8333-444444444444", "createdAt": 300, "cwd": "{{CWD}}", "parentSession": "{{SID}}" },
+      { "type": "session", "id": "eeeeeeee-1111-4222-8333-444444444444", "createdAt": 300, "cwd": "{{CWD}}", "parentSession": "{{SID}}", "delegationDepth": 1 },
       { "type": "request/header", "seq": 0, "time": 6, "data": { "header": { "config": { "model": "fake" }, "system": "SYS PROMPT", "tools": [{ "name": "t1", "description": "D1", "parameters": { "type": "object" } }] }, "reason": "initial" } }
     ]}
   ]
diff --git a/packages/support/acp-snapshot/tests/fixtures/suite/plain-turn/session.1.jsonl b/packages/support/acp-snapshot/tests/fixtures/suite/plain-turn/session.1.jsonl
index a844f891fc..5fb01dbe8a 100644
--- a/packages/support/acp-snapshot/tests/fixtures/suite/plain-turn/session.1.jsonl
+++ b/packages/support/acp-snapshot/tests/fixtures/suite/plain-turn/session.1.jsonl
@@ -1,2 +1,2 @@
-{"type":"session","id":"eeeeeeee-1111-4222-8333-444444444444","createdAt":12,"cwd":"/rec/plain-cwd","parentSession":"56565656-7878-4989-8a9a-9b9b9b9b9b9b"}
+{"type":"session","id":"eeeeeeee-1111-4222-8333-444444444444","createdAt":12,"cwd":"/rec/plain-cwd","parentSession":"56565656-7878-4989-8a9a-9b9b9b9b9b9b","delegationDepth":1}
 {"type":"request/header","seq":0,"time":12,"data":{"header":{"config":{"model":"fake"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
diff --git a/packages/support/acp-snapshot/tests/fixtures/suite/plain-turn/session.jsonl b/packages/support/acp-snapshot/tests/fixtures/suite/plain-turn/session.jsonl
index 744998f959..6bdf784ce2 100644
--- a/packages/support/acp-snapshot/tests/fixtures/suite/plain-turn/session.jsonl
+++ b/packages/support/acp-snapshot/tests/fixtures/suite/plain-turn/session.jsonl
@@ -1,3 +1,3 @@
-{"type":"session","id":"56565656-7878-4989-8a9a-9b9b9b9b9b9b","createdAt":11,"cwd":"/rec/plain-cwd"}
+{"type":"session","id":"56565656-7878-4989-8a9a-9b9b9b9b9b9b","createdAt":11,"cwd":"/rec/plain-cwd","delegationDepth":0}
 {"type":"request/header","seq":0,"time":11,"data":{"header":{"config":{"model":"fake"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
 {"type":"assistant/chunk","seq":1,"time":11,"data":{"turn":1,"step":1,"chunk":{"type":"text-delta","index":0,"text":"hi"}}}
diff --git a/packages/support/acp-snapshot/tests/suite.spec.ts b/packages/support/acp-snapshot/tests/suite.spec.ts
index ac6f944a4a..6fbb06bb9d 100644
--- a/packages/support/acp-snapshot/tests/suite.spec.ts
+++ b/packages/support/acp-snapshot/tests/suite.spec.ts
@@ -90,12 +90,12 @@ function staleRefreshFixtures(dir: string): void {
   writeFileSync(plainBehaviorFile, `${JSON.stringify(plainBehavior, null, 2)}\n`)
 
   writeFileSync(join(dir, 'blocked-log', 'session.jsonl'), [
-    '{"type":"session","id":"99999999-8888-4777-8666-555555555555","createdAt":13,"cwd":"/rec/blocked-cwd"}',
+    '{"type":"session","id":"99999999-8888-4777-8666-555555555555","createdAt":13,"cwd":"/rec/blocked-cwd","delegationDepth":0}',
     '{"type":"hook/result","seq":1,"time":13,"data":{"decision":"stale","durationMs":99}}',
     '',
   ].join('\n'))
   writeFileSync(join(dir, 'authored-error', 'session.jsonl'), [
-    '{"type":"session","id":"77777777-8888-4777-8666-555555555555","createdAt":13,"cwd":"/rec/error-cwd"}',
+    '{"type":"session","id":"77777777-8888-4777-8666-555555555555","createdAt":13,"cwd":"/rec/error-cwd","delegationDepth":0}',
     '{"type":"turn/end","seq":1,"time":9,"data":{"error":"stale"}}',
     '',
   ].join('\n'))
diff --git a/scripts/gen-tool-catalog.ts b/scripts/gen-tool-catalog.ts
index b831004a3b..4840d81dbc 100644
--- a/scripts/gen-tool-catalog.ts
+++ b/scripts/gen-tool-catalog.ts
@@ -79,11 +79,16 @@ class CatalogSearchBashExecutor extends BashExecutor {
   }
 }
 
-/** Register the descriptor needed to mount schema-producing consumers. */
+/**
+ * Register the descriptor needed to mount schema-producing consumers. Declares
+ * the full capability set of the shipped in-process providers so consumers
+ * mount under their shipped defaults (tool-subagent's default numeric maxDepth
+ * requires `depthLimit`).
+ */
 function registerCatalogSubagentProvider(ctx: Context, name: string): void {
   const provider: SubagentProvider = {
     name,
-    capabilities: { outputSchema: false, depthLimit: false, toolFilter: false, persona: false },
+    capabilities: { outputSchema: true, depthLimit: true, toolFilter: true, persona: true },
     inheritsParentContext: false,
     start: () => Promise.reject(new Error('tool-catalog provider cannot start a child')),
   }