Tianyi Cui
b3d40d427e
A fork subagent seeds its child session with a prefix of the parent's log, and that seed becomes the child's persisted log — so a fork child's .jsonl begins with the PARENT's events, including the parent's assistant/chunk events. The snapshot replay harness derived a child's script from its whole log, which would replay the parent's recorded responses as the child's model calls. Spawn-only scenarios never hit it, but a fork snapshot would mis-route silently. Record the seed boundary and skip the inherited prefix at replay: - SessionHeader gains an optional `seedLength` (how many leading events were inherited via a seed), threaded through CreateSessionOptions/CreateAgentOptions meta and stamped by the fork backend (= seeded-prefix length; absent for spawn). It is EXPLICIT, never inferred from seed.length: a resume seeds the whole stored log, so the resume path passes the persisted boundary back. - Both persistence backends round-trip it: JSONL header line, SQLite seed_length column. The SQLite table change bumps SCHEMA_VERSION 2->3; per the pre-release stance the backend rejects an older user_version on open with NO migration. - llm-replay's parseSessionHeader reads seedLength and loadSessionScripts derives a child script from events AFTER the boundary. seedLength is 0 for spawn, so spawn replay is byte-for-byte unchanged. Closes the routing-correctness gap the per-session snapshot replay RFC under- stated; a recorded fork scenario remains a future addition but now derives correctly. RFC: docs/rfc/implemented/testing/2026-06-22-fork-child-replay-seed-boundary.md. Regression coverage: a fork child fixture whose seeded prefix carries a parent chunk (derived script must exclude it, proven red without the slice); a seedLength persistence round-trip through the shared coordinator contract (both backends); the fork backend stamping it; resume preserving it from the persisted header.
subagent/ — subagent capability family
The subagent seam: an agent delegating work to a child agent. Like the bash and llm families this is a capability seam (see capability seams) — but with one defining difference: multiple provider implementations coexist in one context, registered by name, rather than the single-implementation bash shape. The registry mirrors the LLM adapter registry.
| Package | Role | ctx key |
|---|---|---|
subagent/ |
Abstract subagent seam: named-provider registry + vocabulary | ctx.subagents |
subagent-inprocess/ |
Shared in-process run driver (pure lib; registers nothing) | — |
subagent-spawn/ |
In-process backend: a fresh child agent | (registers on ctx.subagents) |
subagent-fork/ |
In-process backend: a child seeded with the parent's completed-turn prefix | (registers on ctx.subagents) |
subagent-acp/ |
Out-of-process backend: a child agent in a spawned subprocess, driven over ACP | (registers on ctx.subagents) |
tool-subagent/ |
Model-facing subagent delegation tool over ctx.subagents |
(registers on ctx.tools) |
The interface lives at subagent/subagent/. The in-process subagent-spawn / subagent-fork backends share the subagent-inprocess driver (a pure library — both depend on it, neither on the other), and the out-of-process subagent-acp backend ships alongside them here; the test-only dsh-subagent-mock (in support) is separate. All product packages except the mock.
The proposal and design rationale: docs/rfc/implemented/feature/2026-06-21-subagent-capability-seam.md.