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.
@deepseek-ai/dsh-subagent-fork
The in-process fork subagent backend: a SubagentProvider that runs each child as a child Agent seeded with a prefix of the parent's session log — so the child inherits the parent's conversation context instead of starting fresh. Shares the run driver (startInProcessRun) with dsh-subagent-spawn; the only difference is the seed.
The seed boundary (the crux)
At the moment a subagent tool's execute runs, the parent's CURRENT turn is open and unbalanced: the log holds the assistant/message carrying this spawn's tool-call and the dangling tool/call with no tool/result yet. Seeding that raw prefix would give the child an open turn that the session constructor and the dev-mode invariants replay reject.
So the fork seeds only the balanced completed-turn prefix — the parent's log up to and including its last turn/end, excluding the in-flight turn entirely (completedTurnPrefix). Because the live log keeps seq === index, the slice is contiguous-from-0 and a valid seed. A parent on its very first (not-yet-complete) turn forks an empty seed — i.e. effectively a fresh child.
The seam this rides on: CreateAgentOptions.seed (added on dsh-agent, threaded through AgentLoop.createAgent → ctx.sessions.prepare({ seed })), the same primitive resume uses.
Capabilities
{ outputSchema: false, depthLimit: true, toolFilter: false } — identical to spawn (the depth/model/output behavior is the shared driver's).
Config
| Key | Meaning |
|---|---|
providerName |
Registry name on ctx.subagents (default fork). |
See dsh-subagent-spawn for the run lifecycle, model inheritance, and depth tracking — all shared.