Hypatia May
b341155652
A plugin owning a standalone open/close bracket cannot tell a dead marker from a live one: an unmatched `compact/start` reads identically whether the previous writer died mid-compaction or a compaction is running now. `Session.firstLiveSeq` already holds that answer exactly, but only in memory. Append the log-only `session/inherited` event at that seq from the seeded constructor — the single waist all six seeded-start paths pass through (resume, configured startup on a persisted id, `sessions.fork()`, a subagent fork child, `adopt()`'s live prefix, and a bare seeded `create`). Read it through the new `isInheritedSeq(events, seq)`. The constructor placement means persistence needs no changes: the marker is already in `events` when a backend captures the creation seed, so it rides the ordinary seed path with no load-time write. It also covers fork, where the inherited bracket's owner may still be running — the case a persistence-layer boundary could not reach. Activity ordering excludes the boundary through `lastActivityTime()`, since lazy resume makes browsing a pickup and the three call sites would otherwise float every opened session to the top of a picker or list.
subagent/ — subagent capability family
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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 (no provider; one cleanup effect per run) | — |
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) |
subagent-dsh-sdk/ |
Out-of-process backend: a child harness runtime in a spawned subprocess, driven over stdio JSON-RPC through the TypeScript SDK client | (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 library with no provider of its own — both depend on it, neither on the other), and the out-of-process subagent-acp / subagent-dsh-sdk backends spawn their children through the subprocess/ seam (the shared credential scrub, tree-scoped teardown, and dispose ladder). Tests replace only the child boundary with package-local fixtures.
The proposal and design rationale: .agents/notes/implemented/feature/2026-06-21-subagent-capability-seam.md.