Merge commit 'refs/codex/unblock/master-current' into HEAD

# Conflicts:
#	docs/config-catalog.md
#	packages/session-persistence/session-persistence-jsonl/README.md
#	packages/session-persistence/session-persistence-jsonl/src/index.ts
#	packages/session-persistence/session-persistence-jsonl/tests/jsonl.spec.ts

docs/core-data-structures/commands.md

@@ -0,0 +1,84 @@
+# Human Commands
+
+The human-command seam of [`dsh-commands`](../../packages/ui/commands). TUI and ACP adapters use it to discover and directly execute plugin-owned commands for an exact agent without creating a model message. The [command Agent Note](../../.agents/notes/implemented/feature/2026-07-19-plugin-command-registration.md) owns dispatch and lifecycle rationale; the [package README](../../packages/ui/commands/README.md) owns composition and limitations.
+
+Source: [`packages/ui/commands/src/index.ts`](../../packages/ui/commands/src/index.ts)
+
+## Input metadata
+
+ACP currently exposes one unstructured-input hint. Command availability follows plugin composition: every adapter consuming the registry sees every effective definition.
+
+```ts type-equiv
+/** Immutable command input metadata compatible with ACP unstructured input. */
+interface CommandInputDescriptor {
+  /** Placeholder shown before the user supplies free-form input. */
+  readonly hint: string
+}
+```
+
+## Definition
+
+`CommandDefinition` is the plugin-authored registration. The registry validates and freezes a detached effective definition.
+
+```ts type-equiv
+/** Plugin-owned command registration. */
+interface CommandDefinition {
+  /** Lowercase command name without the leading slash. */
+  readonly name: string
+  /** Human-readable summary used in discovery UI. */
+  readonly description: string
+  /** Optional free-form input hint advertised to capable clients. */
+  readonly input?: CommandInputDescriptor
+  /** Execute against the receiving agent without sending the command to the model. */
+  readonly handler: (invocation: CommandInvocation) => CommandResult | Promise<CommandResult>
+}
+```
+
+## Invocation and result
+
+The adapter owns cancellation and passes the exact target agent. `rawInput` begins immediately after the parsed name and retains the adapter-delivered separator and suffix. Results are direct UI outcomes, not tool results or session events.
+
+```ts type-equiv
+/** Invocation passed to one registered command handler. */
+interface CommandInvocation {
+  /** Exact agent whose human-facing surface received the command. */
+  readonly agent: Agent
+  /** Exact text following the registered command name, including separator whitespace. */
+  readonly rawInput: string
+  /** Cancellation signal owned by the dispatching UI request. */
+  readonly signal: AbortSignal
+}
+```
+
+```ts type-equiv
+/** Expected command outcome rendered directly by the dispatching UI. */
+type CommandResult =
+  | { readonly kind: 'success'; readonly text?: string }
+  | { readonly kind: 'error'; readonly text: string }
+```
+
+## Discovery and parsing views
+
+Adapters receive handler-free immutable descriptors after scope resolution. `parseCommand()` returns `ParsedCommand` before registry resolution; syntax-valid input can still name an unavailable command.
+
+```ts type-equiv
+/** Handler-free immutable command view returned to UI adapters. */
+interface CommandDescriptor {
+  /** Lowercase command name without the leading slash. */
+  readonly name: string
+  /** Human-readable summary used in discovery UI. */
+  readonly description: string
+  /** Optional free-form input hint advertised to capable clients. */
+  readonly input?: CommandInputDescriptor
+}
+```
+
+```ts type-equiv
+/** Syntactically valid slash command before registry resolution. */
+interface ParsedCommand {
+  /** Lowercase command name without the leading slash. */
+  readonly name: string
+  /** Exact text following the command name. */
+  readonly rawInput: string
+}
+```

docs/core-data-structures/core.md

@@ -18,6 +18,8 @@ Everything else is documented on a **sub-page**, not here. The rule that draws t
 | [llm-streaming.md](llm-streaming.md) | the `StreamChunk` wire protocol + adapter contract, `BlockAssembler`, the `LlmAdapter` seam |
 | [token-meter.md](token-meter.md) | immutable scalar and positional replay measurements with consumed-log revisions |
 | [scope.md](scope.md) | scoped registration identity, dispatch carriers, and the owned `Scope` context |
+| [goal.md](goal.md) | persisted goal identity, lifecycle snapshots, activation, change records, and round attribution |
+| [commands.md](commands.md) | the human-command seam: definitions, adapter discovery, direct invocation, results, and parsing views |
 | [session.md](session.md) | the full `SessionEventMap` variant catalog, `TurnTrigger`/`TurnEndReason`, `deriveMessages()`, the turn-enclosure invariant |
 | [persistence.md](persistence.md) | the durability seam: `SessionPersistence`, JSONL + SQLite backends, `session/flush`, crash recovery, `SessionHeader` |
 | [session-query.md](session-query.md) | logical records, bounded exact-event reads, and relationship traces |
@@ -29,6 +31,7 @@ Everything else is documented on a **sub-page**, not here. The rule that draws t
 | [sandbox.md](sandbox.md) | the process-confinement seam: file-effect modes, `SandboxPolicy`, `ConfinedArgv`, enforcement and fail-closed errors |
 | [code-runtime.md](code-runtime.md) | the code-execution seam: `CodeRunRequest`/`Result`, binding namespaces, captured logs, the `CodeRunFailure` taxonomy |
 | [filesystem.md](filesystem.md) | the filesystem seam: `FsTarget`, read/write/edit outcomes, observed-file state, `FsErrorCode` |
+| [lsp.md](lsp.md) | the LSP navigation seam: `LspQueryRequest`/`Result`, `LspProvider`/`Service`, four operations, `LspError` |
 | [skills.md](skills.md) | the skill service: discovery priority, `SkillSummary`/`SkillDefinition`, session-prefix catalog, model-facing `skill` loading |
 | [compaction.md](compaction.md) | the compaction seam: the `compact/*` session events, `CompactionResult`, the `CompactService` interface |
 | [subagent.md](subagent.md) | the subagent seam: the named-provider registry, `SubagentStartRequest`/`Result`/`Run`, the start-time-vs-runtime capability split |
@@ -190,6 +193,16 @@ interface LlmModelInfo {
 }
 ```
 
+Correctness-sensitive model capacity is queried separately from the advisory catalog and is owned by the adapter serving the exact route.
+
+```ts type-equiv
+/** Provider-owned context capacity for one exact provider/model route. */
+interface LlmModelContext {
+  /** Maximum combined request and response context in tokens. */
+  contextWindow: number
+}
+```
+
 ```ts type-equiv
 /** A single model request, fully assembled. */
 interface GenerateOptions {
@@ -224,7 +237,7 @@ interface GenerateOptions {
 }
 ```
 
-Why a model response stopped is a merge-extensible reason:
+Why a model response stopped is a merge-extensible reason. Terminal provider failures carry the streaming contract's [`LlmFailure`](llm-streaming.md#llmfailure):
 
 ```ts type-equiv
 /**
@@ -235,8 +248,8 @@ interface FinishReasonMap {
   'stop': { kind: 'stop' }
   'tool-calls': { kind: 'tool-calls' }
   'max-tokens': { kind: 'max-tokens' }
-  'aborted': { kind: 'aborted' }
-  'error': { kind: 'error'; message: string; code?: string }
+  'aborted': { kind: 'aborted'; failure: LlmFailure }
+  'error': { kind: 'error'; failure: LlmFailure }
 }
 ```
 
@@ -360,15 +373,20 @@ interface Agent {
   readonly ctx: Context
 
   /**
-   * Queue detached, frozen lossless-JSON input; starts a turn when idle.
+   * Queue one detached, frozen lossless-JSON item. If claimed, it is the sole
+   * ordinary message in its FIFO-ordered turn; the next claimed item waits for
+   * that turn's checkpoint.
    * Invalid input throws synchronously before notification or enqueue.
    */
   send(content: ContentBlock[], options?: SendOptions): void
 
   /**
-   * Steer a running turn: content is injected between steps of the current
-   * turn. Uses the same owned-value and synchronous-validation boundary as
-   * {@link send}; when idle, behaves exactly like that method.
+   * Submit steering while the agent is `running`. An open turn records it at
+   * the next steering checkpoint before a request or continuation decision;
+   * policy may stop before another step. After turn close and its checkpoint,
+   * any remainder is queued for a later turn; terminal `agent/turn-stop`,
+   * cancellation, or disposal may discard it. Uses the same synchronous
+   * snapshot-and-validation boundary as {@link send}; when idle, delegates to it.
    */
   steer(content: ContentBlock[], options?: SendOptions): void
 
@@ -382,8 +400,9 @@ interface Agent {
   inject(content: ContentBlock[], options?: InjectOptions): void
 
   /**
-   * Clear queued and steering work, including work waiting to start, and abort
-   * the active step. The supplied reason is preserved across pre-step and active
+   * Clear all queued and steering work, including items waiting to start, and
+   * abort the active step. An effective call first emits `agent/cancel-requested`
+   * with the resolved reason. That reason is preserved across pre-step and active
    * cancellation windows, and `whenIdle()` resolves after cancellation reaches
    * quiescence. Idle cancellation is a no-op and does not arm a later cancel.
    */
@@ -395,7 +414,7 @@ interface Agent {
 }
 ```
 
-`AgentStatus` is `'idle' | 'running' | 'disposed'`, and `SessionId` is branded. `AgentOptions` is merge-extensible and currently includes `provider?` and `model?`; dispatch requires both after `agent/request`. Persona belongs to `dsh-system-prompt`: an agent-scoped `deployment:persona` may shadow the global default.
+`AgentStatus` is `'idle' | 'running' | 'disposed'`, and `SessionId` is branded. `running` describes the driver-wide drain interval, which can span turn close, its durability checkpoint, and consecutive queued turns; it does not prove a turn is still open. `AgentOptions` is merge-extensible and currently includes `provider?` and `model?`; dispatch requires both after `agent/request`. Persona belongs to `dsh-system-prompt`: an agent-scoped `deployment:persona` may shadow the global default.
 
 The [event taxonomy](../architecture.md#event) owns the `agent/*` lifecycle, checkpoint, and waterfall contracts. Turn and step boundaries are durable session events rather than agent emits.
 
@@ -419,13 +438,14 @@ interface HookContext {
 }
 ```
 
-`agent/prompt-submit` returns a `PromptDecision` (allow a drained queued message — optionally rewriting its `content` or attaching `additionalContexts` — or block it; a batch whose every prompt is blocked opens a zero-step turn that ends `rejected`):
+`agent/prompt-submit` returns a `PromptDecision` (allow the turn's claimed queued message — optionally rewriting its `content` or attaching `additionalContexts` — or record `prompt/blocked` and end that zero-step turn as `rejected`):
 
 ```ts type-equiv
 /**
  * Prompt interception result. `allow.content` replaces the prompt and each
- * `additionalContexts` entry becomes a separate context message. `block` records a
- * durable `prompt/blocked`; an all-blocked batch ends a zero-step rejected turn.
+ * `additionalContexts` entry becomes a separate context message. `block`
+ * records a durable `prompt/blocked` and ends the claimed prompt's zero-step
+ * turn as rejected.
  */
 type PromptDecision =
   | { kind: 'allow'; content?: ContentBlock[]; additionalContexts?: HookContext[] }
@@ -441,14 +461,14 @@ type ContinuationDecision =
   | { action: 'continue'; reason?: { content: ContentBlock[]; source: MessageSource } }
 ```
 
-`agent/request-error` receives the original `RequestError`, whose optional provider-neutral `code` supports stable routing without message parsing:
+`agent/request-error` receives the exact original `RequestError` beside its immutable `LlmFailure`, an immutable list of failures that already authorized another request in the consecutive sequence, the turn signal, and `next()`. Recovery plugins route on `failure.code`, not the live error's message; each policy counts only its own codes, and a successful request clears the history:
 
 ```ts type-equiv
 /** Model-request failure with an optional machine-routable provider code. */
 type RequestError = Error & { code?: string }
 ```
 
-It returns a `RequestErrorDecision`; `retry` opens a new numbered step after the recovery listener's durable mutation, while `fail` preserves that error:
+It returns a `RequestErrorDecision`; `retry` opens a new numbered step after the recovery listener's durable mutation, while `fail` retains the structured failure on `turn/end`:
 
 ```ts type-equiv
 /** Failed-request recovery decision; `retry` opens another numbered step while listeners delegate by calling `next()`. */

docs/core-data-structures/goal.md

@@ -0,0 +1,143 @@
+# Same-session goals
+
+Types shared by the event-sourced goal domain and its policy consumers. The [goal-domain Agent Note](../../.agents/notes/implemented/feature/2026-07-19-persisted-same-session-goal-domain.md) owns the persistence and activation decisions; this page records the literal shapes from [`packages/goal/goal/src/types.ts`](../../packages/goal/goal/src/types.ts).
+
+## Identity and lifecycle
+
+`GoalId` is a [branded id](core.md#branded-ids). A caller mutates one exact revision through `GoalRef`; every accepted durable mutation increments the revision.
+
+```ts type-equiv
+/** Compare-and-set identity for one exact goal revision. */
+interface GoalRef {
+  /** Stable goal identity. */
+  readonly id: GoalId
+  /** Positive revision; every durable mutation increments it. */
+  readonly revision: number
+}
+```
+
+The durable phase answers what happened to the objective. Process-local activation separately answers whether a continuation consumer may start another round.
+
+```ts type-equiv
+/** Durable continuation phase. Activation is process-local and separate. */
+type GoalPhase =
+  | 'active'
+  | 'paused'
+  | 'blocked'
+  | 'complete'
+```
+
+Blocking is the single durable stopped-by-a-problem state. Its policy-owned reason carries a stable lower-kebab-case code for routing and a free-form explanation for humans and models.
+
+```ts type-equiv
+/** Machine-routable and human-readable explanation for a blocked goal. */
+interface GoalBlockReason {
+  /** Stable lower-kebab-case classification chosen by the blocking policy. */
+  readonly code: string
+  /** Non-empty explanation shown to humans and models. */
+  readonly message: string
+}
+```
+
+```ts type-equiv
+/** Full durable state written by every non-clear goal mutation. */
+interface GoalSnapshot extends GoalRef {
+  /** Human-requested completion objective. */
+  readonly objective: string
+  /** Durable lifecycle phase. */
+  readonly phase: GoalPhase
+  /** Present exactly while `phase` is `blocked`. */
+  readonly blockedReason?: GoalBlockReason
+  /** Total admitted goal-round cap. */
+  readonly maxGoalRounds: number
+}
+```
+
+```ts type-equiv
+/** Current goal projection, including values derived from the session log. */
+interface GoalView extends GoalSnapshot {
+  /** Highest admitted round number for this goal. */
+  readonly roundsStarted: number
+  /** Epoch milliseconds of the create mutation. */
+  readonly createdAt: number
+  /** Epoch milliseconds of the latest mutation. */
+  readonly updatedAt: number
+  /** Process-local continuation eligibility; never persisted. */
+  readonly activation: GoalActivation
+}
+```
+
+## Durable changes
+
+Every mutation is a `context/message` whose metadata is either a complete snapshot or a clear tombstone. The version, metadata, goal source, and verbatim rendered content form one replay invariant.
+
+```ts type-equiv
+/** Full-snapshot goal mutation retained in a model-visible context event. */
+interface GoalSnapshotChangeMeta {
+  readonly kind: 'goal/change'
+  readonly version: 1
+  readonly operation: Exclude<GoalOperation, 'clear'>
+  readonly goal: GoalSnapshot
+  readonly roundsStarted: number
+  readonly createdAt: number
+  readonly updatedAt: number
+}
+```
+
+```ts type-equiv
+/** Tombstone retained when the current goal is cleared. */
+interface GoalClearChangeMeta {
+  readonly kind: 'goal/change'
+  readonly version: 1
+  readonly operation: 'clear'
+  readonly cleared: GoalRef
+  readonly clearedAt: number
+}
+```
+
+Goal state changes use round `0`. A continuation consumer attributes each admitted user-message turn with a positive, sequential round number and the current revision; replay rejects gaps, stale revisions, stopped phases, and cap overflow.
+
+```ts type-equiv
+/** Message attribution for durable goal state and continuation rounds. */
+interface GoalMessageSource {
+  readonly kind: 'goal'
+  readonly goalId: GoalId
+  readonly revision: number
+  /** Zero for state changes; positive for admitted continuation rounds. */
+  readonly round: number
+}
+```
+
+## Requests and notifications
+
+Creation separates caller omission from the deployment choice, which `create()` resolves internally. An edit is a partial replacement whose runtime validator requires at least one field. Every mutation notification carries the accepted operation and exact revision; clear omits `goal`.
+
+```ts type-equiv
+/** Input whose omitted round cap is resolved by the service configuration. */
+interface CreateGoalRequest {
+  readonly objective: string
+  readonly maxGoalRounds?: number
+}
+```
+
+```ts type-equiv
+/** Fields changed by an edit; at least one must be present. */
+interface EditGoalRequest {
+  readonly objective?: string
+  readonly maxGoalRounds?: number
+}
+```
+
+```ts type-equiv
+/** Live notification after one goal mutation has been accepted for logging. */
+interface GoalChanged {
+  readonly operation: GoalOperation
+  readonly ref: GoalRef
+  /** Absent for a clear tombstone. */
+  readonly goal?: GoalView
+}
+```
+
+## Service behavior
+
+[`GoalService`](../../packages/goal/goal/src/index.ts) resolves creation defaults, folds strict replay, enforces exact-live-agent identity and compare-and-set mutations, overlays deferred injections, and emits contained `goal/changed` notifications. The package [README](../../packages/goal/goal/README.md) owns the callable and model-visible contract.

docs/core-data-structures/llm-streaming.md

@@ -31,18 +31,40 @@ type StreamChunk =
   }
 ```
 
+## `LlmFailure`
+
+Every thrown or in-band final-adapter failure normalizes to one serializable provider-neutral payload. `providerRetryAfterMs` is a validated positive delay requested by the provider, not a retry decision; `ProviderRequestId` is an opaque branded string for diagnostics.
+
+```ts type-equiv
+/** Serializable provider-boundary facts; policy decides whether they are retryable. */
+interface LlmFailure {
+  /** Human-readable provider or transport failure. */
+  readonly message: string
+  /** Stable provider-neutral machine-routing code. */
+  readonly code: string
+  /** HTTP status observed at the provider boundary, when available. */
+  readonly status?: number
+  /** Provider-requested delay in milliseconds, when valid and available. */
+  readonly providerRetryAfterMs?: number
+  /** Opaque provider-issued request identifier for diagnostics. */
+  readonly requestId?: ProviderRequestId
+}
+```
+
 ## The adapter contract
 
 Every adapter MUST obey these, and every consumer may rely on them:
 
 - **`usage` before `finish`, nothing after `finish`.** Defer both to the provider's end-of-stream marker so a trailing usage-only chunk can't violate the ordering.
 - **Tool-call `arguments` stay raw JSON strings end-to-end.** Partial fragments stream via `argumentsDelta`; a provider that hands back parsed objects re-stringifies at `block-end`.
-- **Two sanctioned error paths.** A failure may either THROW from `stream()` (transport/protocol errors) **or** end the stream with `finish {kind:'error'|'aborted'}` (provider in-band errors, for adapters that can't throw mid-stream). Consumers must handle *both*. The agent loop closes the failed step and offers either form to `agent/request-error`; absent recovery it becomes a turn error, and no normal completed assistant message is logged for that request.
+- **Two sanctioned error paths, one fact shape.** A failure may either THROW from `stream()` (transport/protocol errors) **or** end the stream with `finish {kind:'error'|'aborted', failure}` (provider in-band errors, for adapters that can't throw mid-stream). `LlmError.failure` carries the same `LlmFailure`. The final adapter boundary preserves the exact thrown `Error` object and associates immutable facts with that call; the agent loop closes the failed step and offers the error, facts, and immutable prior-retried facts to `agent/request-error`. Absent recovery the structured failure becomes the turn error, and no normal assistant message or tool side effect is committed for that attempt.
+- **One adapter call is one provider attempt.** Adapters disable library retries. Agent-level recovery opens another durable numbered step; direct `ctx.llm.stream()` callers remain single-attempt.
+- **Provider stalls are bounded at the transport.** Both shipping remote adapters expose positive finite `streamIdleTimeoutMs` with a five-minute default. The watchdog arms only while iterator `next()` is outstanding, uses one stable signal for the whole request, maps its own expiry to `TIMEOUT`, and keeps an earlier caller abort as `ABORTED`.
 - **Context overflow has one canonical code.** Both DeepSeek adapters classify explicit provider detail through `isContextWindowExceededError()` and surface `CONTEXT_WINDOW_EXCEEDED`, whether the failure arrives as a thrown HTTP `LlmError` or an in-band finish error. Consumers route on the code, never provider text.
 - **Every provider HTTP request carries the app-attribution header.** Adapters send `attributionHeaders()` (below) - the `User-Agent` baseline - and prove it with a wire-level test (mock server asserting the received header, or the library's header hook for a library-backed adapter).
 - **Replay state is adapter-owned.** A successful `finish` may carry lossless-JSON state needed to reconstruct a native provider response. The loop stores it with the assembled assistant message unless an `agent/step-result` listener rewrote the content. On a later request, `LlmService` passes the state only when the historical provider and target provider are currently registered to the exact same adapter instance. That adapter validates the state and owns any cross-model or cross-provider conversion; other adapters receive the provider-neutral content and provenance without the private state.
 
-This contract was pinned down by two deliberately independent implementations: `dsh-llm-deepseek` (hand-rolled fetch/SSE) and `dsh-llm-pi-ai` (a generic multi-provider adapter through `@earendil-works/pi-ai`). The library-backed adapter cannot throw mid-stream, so it exercises the finish-chunk error path the hand-rolled one might not.
+This contract is pinned down by two deliberately independent implementations: `dsh-llm-deepseek` (hand-rolled fetch/SSE) and `dsh-llm-pi-ai` (a generic multi-provider adapter through `@earendil-works/pi-ai`). The library-backed adapter exercises the finish-chunk error path, while transport-boundary tests prove each idle watchdog stops its actual request.
 
 ## `AppIdentity` — app attribution
 
@@ -132,7 +154,7 @@ declare class BlockAssembler {
 
 ## The seam
 
-`LlmAdapter` is the provider seam: subclass, implement `stream()`, and register one adapter instance with `ctx.llm.registerAdapter(providers, adapter)`. `GenerateOptions.provider` selects the registered adapter; `GenerateOptions.model` is passed to that adapter and need not be registered at lifecycle start. Duplicate provider routes fail atomically. Optional `providerInfo()` and asynchronous `listModels()` methods feed `LlmService.listProviders()` / `listModels()` with detached selector metadata. That catalog is advisory rather than a request whitelist: the adapter remains authoritative and may accept unlisted model ids. Adapter lookup happens at the terminal continuation of the `llm/stream` waterfall, so a listener may short-circuit the call or route a mutable one-shot request before lookup. The `block-start` / `block-end` `index` correlation and the assembler together mean an adapter only has to emit well-formed chunks — block reassembly is not each adapter's problem. The consumer surface (`ctx.llm.stream()`) and the `llm/stream` waterfall are described in [architecture.md § Content blocks and streaming](../architecture.md#content-blocks-and-streaming-dsh-llm).
+`LlmAdapter` is the provider seam: subclass, implement `stream()`, and register one adapter instance with `ctx.llm.registerAdapter(providers, adapter)`. `GenerateOptions.provider` selects the registered adapter; `GenerateOptions.model` is passed to that adapter and need not be registered at lifecycle start. Duplicate provider routes fail atomically. Optional `providerInfo()` and asynchronous `listModels()` methods feed `LlmService.listProviders()` / `listModels()` with detached selector metadata. That catalog is advisory rather than a request whitelist: the adapter remains authoritative and may accept unlisted model ids. The separate `resolveModelContext()` query exposes correctness-sensitive capacity for an exact route without making catalog membership authoritative; absence means unknown metadata, not invalid routing. Adapter lookup happens at the terminal continuation of the `llm/stream` waterfall, so a listener may short-circuit the call or route a mutable one-shot request before lookup. The `block-start` / `block-end` `index` correlation and the assembler together mean an adapter only has to emit well-formed chunks — block reassembly is not each adapter's problem. The consumer surface (`ctx.llm.stream()`) and the `llm/stream` waterfall are described in [architecture.md § Content blocks and streaming](../architecture.md#content-blocks-and-streaming-dsh-llm).
 
 ```ts public-api
 /**
@@ -156,6 +178,17 @@ declare abstract class LlmAdapter {
    * @returns discoverable models in adapter-preferred order.
    */
   listModels(_provider: string): Promise<readonly LlmModelInfo[]>;
+  /**
+   * Resolve context capacity for one model accepted by this adapter. Absence
+   * means the adapter does not know the capacity, not that routing is invalid.
+   * @param _provider - one provider route owned by this adapter.
+   * @param _model - exact model id passed to {@link GenerateOptions.model}.
+   * @returns provider-owned context metadata, or `undefined` when unavailable.
+   */
+  resolveModelContext(
+    _provider: string,
+    _model: string,
+  ): Promise<LlmModelContext | undefined>;
   /**
    * Stream one model call as raw chunks. The only required method.
    * @param options - the fully-assembled request; implementations must honor `options.signal`.

docs/core-data-structures/lsp.md

@@ -0,0 +1,163 @@
+# LSP navigation
+
+The LSP seam — a [capability seam](../../.agents/notes/implemented/architecture/2026-07-15-lsp-capability-seam.md) exposing semantic code navigation on one `ctx.lsp` service, split across packages: interface ([dsh-lsp](../../packages/lsp/lsp), `ctx.lsp` + the provider registry), a generic implementation ([dsh-lsp-local](../../packages/lsp/lsp-local), a configured stdio language-server host), and consumer ([dsh-tool-lsp](../../packages/lsp/tool-lsp), the `lsp` tool schema). LSP is **one optional capability**, not part of the agent-loop spine — so its vocabulary lives here, not in [core.md](core.md). A provider swap does not change how the model asks for navigation.
+
+Source: [`packages/lsp/lsp/src/types.ts`](../../packages/lsp/lsp/src/types.ts)
+
+## Operations and coordinates
+
+The seam and model expose exactly four semantic queries; the union is closed, so adding one is a compile-enforced change across the seam, providers, and the tool. Positions and ranges are zero-based UTF-16, matching the protocol; the model-facing tool owns the one-based cursor convention and converts on the way in and out.
+
+```ts type-equiv
+/**
+ * The four semantic queries the seam and model expose. A closed union: adding an operation is a
+ * compile-enforced change across the seam, providers, and the tool. Symbols and call hierarchy are
+ * deliberately deferred (they need different schemas).
+ */
+type LspOperation = 'goToDefinition' | 'findReferences' | 'goToImplementation' | 'hover'
+```
+
+```ts type-equiv
+/** A zero-based UTF-16 cursor coordinate, matching the LSP wire convention. */
+interface LspPosition {
+  /** Zero-based line. */
+  readonly line: number
+  /** Zero-based UTF-16 code-unit offset within the line. */
+  readonly character: number
+}
+```
+
+```ts type-equiv
+/** A zero-based UTF-16 half-open range `[start, end)`. */
+interface LspRange {
+  readonly start: LspPosition
+  readonly end: LspPosition
+}
+```
+
+## Request
+
+Every field is required: `workspaceRoot` is caller-supplied, `languageId` comes from the provider's registration (not the request), and consumers own timeouts and result limits — so no field needs implementation defaulting and there is no `resolve()` step. The provider receives the caller's request plus the derived `languageId`, which only synchronizes the transient document and never participates in selection.
+
+```ts type-equiv
+/**
+ * A caller's normalized query. Every field is required: `workspaceRoot` is caller-supplied,
+ * `languageId` comes from the provider registration (not here), and consumers own timeouts and
+ * result limits — so no field needs implementation defaulting and there is no `resolve()` step.
+ */
+interface LspQueryRequest {
+  /** Which semantic query to run. */
+  readonly operation: LspOperation
+  /** The source file to query (relative to `workspaceRoot` or absolute; the provider canonicalizes). */
+  readonly filePath: string
+  /** The zero-based UTF-16 cursor position to query at. */
+  readonly position: LspPosition
+  /** The workspace root the provider resolves against and indexes; required, never defaulted. */
+  readonly workspaceRoot: string
+}
+```
+
+```ts type-equiv
+/**
+ * A request as a provider receives it: the caller's {@link LspQueryRequest} plus the `languageId`
+ * the seam derived from the provider's extension mapping. The language id only synchronizes the
+ * transient document; it does not participate in selection.
+ */
+interface LspProviderQuery extends LspQueryRequest {
+  /** The LSP language id for `filePath`, from this provider's extension mapping. */
+  readonly languageId: string
+}
+```
+
+## Result
+
+A CLOSED discriminated union: navigation operations normalize to `locations`, `hover` to content or `null`. Consumers `switch` on `kind` to exhaustiveness so a new arm breaks compilation until handled. `findReferences` always includes declarations — the provider enforces this internally, so callers get no flag. The `locations` variant carries `resolvedWorkspaceRoot`: the provider's canonical form of the request's `workspaceRoot` and the root its `file:` URIs are relative to, so a caller relativizing display paths uses it rather than the possibly-symlinked request root.
+
+```ts type-equiv
+/** One resolved location: a document URI and the range within it. */
+interface LspLocation {
+  /** The target document URI (`file:` or otherwise), verbatim from the server. */
+  readonly uri: string
+  /** The range within the target document. */
+  readonly range: LspRange
+}
+```
+
+```ts type-equiv
+/** Normalized hover content, or `null` for no hover at the position. */
+interface LspHover {
+  /** The normalized hover text (markdown or plaintext, provider-joined). */
+  readonly contents: string
+  /** The range the hover applies to, when the server supplied one. */
+  readonly range?: LspRange
+}
+```
+
+```ts type-equiv
+/**
+ * The closed result union. Navigation operations (`goToDefinition`, `findReferences`,
+ * `goToImplementation`) normalize to `locations`; `hover` normalizes to content or `null`.
+ * Consumers `switch` on `kind` to exhaustiveness so a new arm breaks compilation until handled.
+ *
+ * The `locations` variant carries `resolvedWorkspaceRoot`: the provider's canonical form of the
+ * request's `workspaceRoot`, and the root its `file:` location URIs are relative to. A caller that
+ * relativizes display paths MUST use this, not the request's (possibly symlinked) `workspaceRoot`;
+ * otherwise a symlinked workspace misclassifies in-workspace results as external.
+ */
+type LspQueryResult =
+  | { readonly kind: 'locations'; readonly locations: readonly LspLocation[]; readonly resolvedWorkspaceRoot: string }
+  | { readonly kind: 'hover'; readonly hover: LspHover | null }
+```
+
+## Provider and service
+
+A provider owns a stable branded `id` and an exclusive lowercase leading-dot extension map. `registerProvider` reserves the id and every extension atomically — an invalid or conflicting registration publishes nothing — and its disposer releases all reservations. Selection is per query and order-independent; no match throws `LspError` `LSP_UNAVAILABLE`. The seam exposes no protocol types, process/document controls, or generic JSON-RPC escape hatch.
+
+```ts type-equiv
+/**
+ * A language-server backend registered on `ctx.lsp`. Each provider owns a stable {@link
+ * LspProviderId} and an extension-to-language-id map (lowercase, leading-dot keys).
+ * `findReferences` always includes declarations — the provider enforces this internally; callers
+ * get no flag.
+ */
+interface LspProvider {
+  /** Stable provider identity, reserved atomically with the extension mappings. */
+  readonly id: LspProviderId
+  /** Lowercase leading-dot extension → LSP language id (e.g. `{ '.ts': 'typescript' }`). */
+  readonly extensionToLanguage: Readonly<Record<string, string>>
+  /**
+   * Run one query. The seam has already selected this provider and derived `languageId`.
+   * @param request - the resolved provider query (caller request + derived language id).
+   * @param signal - optional cancellation; the provider stops its own work when it aborts.
+   * @returns the normalized, closed-union result.
+   */
+  query(request: LspProviderQuery, signal?: AbortSignal): Promise<LspQueryResult>
+}
+```
+
+```ts type-equiv
+/**
+ * The LSP capability seam (`ctx.lsp`). Owns provider registration/selection and normalized query
+ * execution; exposes exactly the four operations and no protocol escape hatch.
+ */
+interface LspService {
+  /**
+   * Register a provider, atomically reserving its id and every normalized extension. Any conflict
+   * or invalid input publishes nothing and throws `LspError`; the returned disposer releases all
+   * reservations. Disposed with the calling fiber.
+   * @param provider - the backend to register.
+   * @returns a synchronous disposer releasing the id and all extension reservations.
+   */
+  registerProvider(provider: LspProvider): () => void
+  /**
+   * Select a provider by the file's extension and run one query. Selection is per-query and
+   * order-independent; no match throws `LspError` `LSP_UNAVAILABLE`.
+   * @param request - the normalized query.
+   * @param signal - optional cancellation forwarded to the selected provider.
+   * @returns the normalized, closed-union result.
+   */
+  query(request: LspQueryRequest, signal?: AbortSignal): Promise<LspQueryResult>
+}
+```
+
+`LspProviderId` is the seam's branded id (`Branded<'LspProviderId'>` from [dsh-brand](../../packages/util/brand)); `LspError` extends `HarnessError` with stable codes such as `LSP_INVALID_PROVIDER`, `LSP_CONFLICT`, `LSP_UNAVAILABLE`, `LSP_DISPOSED`, `LSP_UNSUPPORTED_OPERATION`, and `LSP_MALFORMED_RESPONSE`, which callers route on instead of parsing `message`.

docs/core-data-structures/persistence.md

@@ -6,7 +6,7 @@ The seam is a textbook [capability seam](../../.agents/notes/implemented/archite
 
 ## The flush checkpoint
 
-`session/event` is a *synchronous* notification; persistence plugins buffer it (write-behind) and drain at the awaited `session/flush` checkpoint the loop fires at every turn end. Flush is `ctx.parallel` (awaited): a turn's events are durably committed before the next turn starts, and the turn boundary is the commit boundary. A rejecting flush is reported via `agent/error` and the logger — never as a session event (it would land past the commit boundary), so the backend keeps its buffered events for the next flush.
+`session/event` is a *synchronous* notification; persistence plugins buffer it (write-behind) until `session/flush`. The loop awaits an ordinary turn's checkpoint before claiming the next queue item; synchronous idle `inject()` schedules its checkpoint without blocking `send()`, and disposal still drains it. A successful flush durably commits the closed turn as one unit; a rejecting flush is reported through `agent/error` and the logger — never as a session event past the closed turn — while the backend keeps its buffered events for the next flush.
 
 ## Crash recovery preserves an interrupted turn
 
@@ -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
   }
 }
 ```
@@ -95,5 +102,5 @@ Replay/fork is therefore `ctx.sessions.create(id, { seed: seedEvents })`; resumi
 
 Both implement the same abstract `SessionPersistence` (locate/create/append/load/list over `SessionEvent`) and pass `runPersistenceContract`, proving the seam is genuinely backend-agnostic:
 
-- **[dsh-session-persistence-jsonl](../../packages/session-persistence/session-persistence-jsonl)** — an append-only JSONL log per session with crash-safe atomic writes, the interrupted-turn crash recovery above, and a read/replay path.
+- **[dsh-session-persistence-jsonl](../../packages/session-persistence/session-persistence-jsonl)** — an append-only logical JSONL log per session, stored as checksummed concatenated Zstandard frames by default or raw lines by configuration, with crash-safe atomic writes, interrupted-turn recovery, and a read/replay path.
 - **[dsh-session-persistence-sqlite](../../packages/session-persistence/session-persistence-sqlite)** — `node:sqlite`, one row per `SessionEvent`. The row shape `(session_id, seq, type, time, data, source_event_seqs, surface_op)` maps 1:1 onto the event, including optional surface metadata, so there is no parallel persisted schema to keep in sync.

docs/core-data-structures/session.md

@@ -17,27 +17,28 @@ The append-only event types. Merge-extensible: a plugin declares extra event typ
  */
 interface SessionEventMap {
   /**
-   * Opens turn `turn`. `trigger` records what started it — a drained message
-   * batch or an idle-time injection. The turn is the durability/replay
+   * Opens turn `turn`. `trigger` records what started it — one claimed queued
+   * message or an idle-time injection. The turn is the durability/replay
    * boundary: every event sits between a `turn/start` and its matching
    * `turn/end` (the turn-enclosure invariant).
    */
   'turn/start': { turn: number; trigger: TurnTrigger }
   /**
    * Closes turn `turn` with the {@link TurnEndReason} that ended it. The loop
-   * fires the awaited `session/flush` checkpoint at every turn end, so the turn
-   * boundary is also the durable-commit boundary.
+   * awaits `session/flush` after an ordinary turn ends before claiming the next
+   * queued item. Success commits the turn; rejection is reported live and does
+   * not prevent later work.
    */
   'turn/end': { turn: number; reason: TurnEndReason }
   /** Opens step `step` of turn `turn` — one model call plus the tool executions it requested. */
   'step/start': { turn: number; step: number }
   /** Closes step `step` of turn `turn`. */
   'step/end': { turn: number; step: number }
-  /** A user-visible prompt (queued message drained at turn start). */
+  /** A user-visible prompt (the queued message claimed for this turn). */
   'user/message': { content: ContentBlock[]; source: MessageSource }
   /**
    * Durable record of a prompt veto and its reason. It is log-only: the blocked
-   * prompt never enters the model-visible surface, including in a mixed batch.
+   * prompt never enters the model-visible surface, and its turn runs zero steps.
    */
   'prompt/blocked': { content: ContentBlock[]; source: MessageSource; reason: string }
   /**
@@ -429,7 +430,7 @@ declare class Session {
 - `context/message` → a user-role message carrying its `content` verbatim at its chronological position. Optional JSON `meta` remains in the event log and is never rendered.
 - `steering/message` → a user-role message carrying its content verbatim at its chronological position.
 
-Everything else (`turn/*`, `step/*`) is structural and does not project into a message. Token usage is observed on `assistant/message.usage` (the step that produced it); an operational error's step number is on `turn/end.reason` for `kind: 'error'`. Because this unreleased format intentionally has no compatibility promise, seed/load validation rejects request headers without provider+model and assistant messages without provider/model provenance instead of guessing a route for historical data.
+Everything else (`turn/*`, `step/*`, plugin-owned `llm/retry`) is structural and does not project into a message. Token accounting reads per-step `assistant/chunk { type: 'usage' }` records and treats `assistant/message.usage` as the committed-step fallback when no usage chunk exists; failed model-request attempts have no assistant message, so their usage chunk is the durable accounting record. An operational error's step number is on `turn/end.reason` for `kind: 'error'`, with normalized `LlmFailure` facts for a final model-request failure and message/code for other live errors. Because this unreleased format intentionally has no compatibility promise, seed/load validation rejects request headers without provider+model and assistant messages without provider/model provenance instead of guessing a route for historical data.
 
 ## Live-session fork API
 
@@ -473,15 +474,19 @@ interface TurnEndReasonMap {
    * The turn failed: a step threw or the model reported a failure. `step` is the
    * step number the failure occurred on (the operational error's location — the
    * single durable record of an in-turn failure; live diagnostics also fire via
-   * `agent/error`). `code` is the error's code when one was attached.
+   * `agent/error`). Final model-request failures retain their normalized facts
+   * as one `failure`; other turn failures retain their live Error message/code.
    */
-  error: { kind: 'error'; step: number; message: string; code?: string }
+  error: { kind: 'error'; step: number } & (
+    | { failure: LlmFailure; message?: never; code?: never }
+    | { message: string; code?: string; failure?: never }
+  )
   disposed: { kind: 'disposed' }
   /** At least one step reached its output-token ceiling, even if a plugin continued the turn. */
   'max-tokens': { kind: 'max-tokens' }
   /**
-   * Policy blocked every prompt before the first step. The zero-step turn still
-   * records a balanced durable boundary and the veto reason.
+   * Policy blocked the turn's claimed prompt before the first step. The
+   * zero-step turn still records a balanced durable boundary and veto reason.
    */
   rejected: { kind: 'rejected'; reason: string }
   /**
@@ -492,11 +497,11 @@ interface TurnEndReasonMap {
 }
 ```
 
-`max-tokens` mirrors the model-call `FinishReason` of the same name: any `max-tokens` step in a turn makes the whole turn end `max-tokens` rather than `completed` (the cut-short fact wins over a later continuation), so a consumer can tell a clean stop from a truncated one — but only over `completed`: the `disposed`/`aborted`/`error` outcomes take precedence. `rejected` is a zero-step turn whose whole prompt batch an `agent/prompt-submit` hook blocked (the ACP bridge maps it to `cancelled`). `interrupted` is the one reason no loop emits — it is synthesized by crash recovery (see [persistence.md](persistence.md)). Both maps are merge-extensible.
+`max-tokens` mirrors the model-call `FinishReason` of the same name: any `max-tokens` step in a turn makes the whole turn end `max-tokens` rather than `completed` (the cut-short fact wins over a later continuation), so a consumer can tell a clean stop from a truncated one — but only over `completed`: the `disposed`/`aborted`/`error` outcomes take precedence. `rejected` is a zero-step turn whose claimed prompt an `agent/prompt-submit` hook blocked (the ACP bridge maps it to `cancelled`). `interrupted` is the one reason no loop emits — it is synthesized by crash recovery (see [persistence.md](persistence.md)). Both maps are merge-extensible.
 
 ## The turn-enclosure invariant
 
-Every session event lives **inside** a turn (between a `turn/start` and its `turn/end`). The loop appends queued `user/message` events *after* `turn/start`, and an idle `agent.inject()` wraps its `context/message` in a one-shot `injection` turn. This makes the turn the single durability/replay boundary: a backend can treat anything after the last `turn/end` as an interrupted-crash tail without risking the loss of legitimately-recorded between-turn context. The `dsh-invariants` plugin enforces it in dev (a message event outside an open turn throws). See [the turn-enclosure invariant Agent Note](../../.agents/notes/implemented/architecture/2026-06-15-turn-enclosure-invariant.md).
+Every session event lives **inside** a turn (between a `turn/start` and its `turn/end`). The loop appends queued `user/message` events *after* `turn/start`, and an idle `agent.inject()` wraps its `context/message` in a one-shot `injection` turn. This makes the turn the single durability/replay boundary: a backend can treat anything after the last `turn/end` as an interrupted-crash tail without risking the loss of legitimately-recorded between-turn context. The optional `dsh-session/invariant` companion enforces it in dev through `ctx.invariants` (a message event outside an open turn throws). See [the turn-enclosure invariant Agent Note](../../.agents/notes/implemented/architecture/2026-06-15-turn-enclosure-invariant.md).
 
 ## Plugin-contributed log-only events
 
@@ -506,6 +511,6 @@ The hook bridges' `hook/invoked` / `hook/result` provenance pairs (from `@deepse
 
 ## Durability contract
 
-What a persistence backend relies on: the durable log persists every event verbatim, **including** `assistant/chunk` — `seq` must stay contiguous, so chunks cannot be filtered out of the canonical log. All `event.data` must be JSON-serializable; `Session.append` enforces this at the source (throwing on non-serializable data), so a bad event never enters the log and `session.events` always equals what a backend can persist. Adding an event type that carries non-serializable data, or that breaks the turn/step nesting the invariants plugin checks, is a breaking change to the on-disk format.
+What a persistence backend relies on: the durable log persists every event verbatim, **including** `assistant/chunk` — `seq` must stay contiguous, so chunks cannot be filtered out of the canonical log. All `event.data` must be JSON-serializable; `Session.append` enforces this at the source (throwing on non-serializable data), so a bad event never enters the log and `session.events` always equals what a backend can persist. Adding an event type that carries non-serializable data, or that breaks the turn/step nesting checked by the session invariant companion, is a breaking change to the on-disk format.
 
 The backends that consume this contract are on [persistence.md](persistence.md).

docs/core-data-structures/subagent.md

@@ -49,7 +49,10 @@ interface SubagentStartRequest {
    * The spawning ("parent") agent — the one whose tool call started this
    * subagent. REQUIRED: in-process backends read `parent.session.header` for
    * the working directory, the `parentSession` lineage to stamp on the child,
-   * and the parent's delegation depth. Out-of-process backends (ACP) ignore it.
+   * and the parent's delegation depth. The out-of-process backend (ACP) reads
+   * exactly one field — the session header's cwd, the child's workspace when
+   * no deployment `cwd` override is configured; nothing else crosses the
+   * process boundary.
    */
   readonly parent: Agent
   /**
@@ -237,5 +240,5 @@ 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).

docs/core-data-structures/user-interaction.md

@@ -1,6 +1,6 @@
 # User Interaction
 
-The user-interaction seam of [dsh-user-interaction](../../packages/ui/user-interaction). It is the provider-neutral vocabulary a tool or permission plugin uses when it needs the human to answer before the agent can continue. UI surfaces provide the active `UserInteractionProvider`: `dsh-stdio-demo` selects keyboard-driven `dsh-tui` overlays or `dsh-stdio` readline prompts, and `dsh-acp` maps questions to ACP form elicitations.
+The user-interaction seam of [dsh-user-interaction](../../packages/ui/user-interaction). It is the provider-neutral vocabulary a tool or permission plugin uses when it needs the human to answer before the agent can continue. UI surfaces provide the active `UserInteractionProvider`: `dsh-tui` uses keyboard-driven overlays, and `dsh-acp` maps questions to ACP form elicitations.
 
 Source: [`packages/ui/user-interaction/src/index.ts`](../../packages/ui/user-interaction/src/index.ts)
 

docs/core-data-structures/workflow.md

@@ -8,7 +8,7 @@ Source: [`packages/workflow/workflow/src/types.ts`](../../packages/workflow/work
 
 ## The start request
 
-What a caller asks for when starting a run. The tool layer builds this from the model's `{ script, meta, args }` call plus the calling agent; `meta` and `args` are plain JSON DATA (the engine shape-validates `meta` and rejects loud BEFORE anything runs — no script text is ever evaluated to obtain it). `parent` is REQUIRED — every child the script spawns is attributed to it (cwd, lineage, and depth flow through the [subagent seam](subagent.md)).
+What a caller asks for when starting a run. The ordinary workflow tool builds this from the model's `{ script, meta, args }` call plus the calling agent; specialized consumers may also select one engine-wide `subagentProvider` and lower `maxTotalAgents` for the run, but the script cannot observe or replace either policy. `meta` and `args` are plain JSON DATA (the engine shape-validates `meta` and rejects loud BEFORE anything runs — no script text is ever evaluated to obtain it). `parent` is REQUIRED — every child the script spawns is attributed to it (cwd, lineage, and depth flow through the [subagent seam](subagent.md)).
 
 ```ts type-equiv
 /**
@@ -26,6 +26,17 @@ interface WorkflowStartRequest {
   meta: WorkflowMeta
   /** Optional input exposed verbatim to the script as the `args` global. */
   args?: unknown
+  /**
+   * Optional engine-wide child-provider override for this run. The workflow
+   * script cannot observe or replace it; omission uses the engine's configured
+   * provider.
+   */
+  subagentProvider?: string
+  /**
+   * Optional per-run total-child ceiling. Implementations reject values above
+   * their deployment ceiling before publishing the run.
+   */
+  maxTotalAgents?: number
   /** The agent on whose behalf the run executes (parent of every child). */
   parent: Agent
   /** Cancels the run when aborted (the tool's `exec.signal`). */