an endpoint for spawning an agent, so a caller that is not a chat can

A chat agent already has a way to start a worker — the harness gives it one.
Nothing else does. A watcher loop, a plugin, a background job, a cron entry: none
can reach that tool, which is exactly why a commander's loop shells out to
`claude -p` by hand and then invents its own record-keeping for what it started.

So this is the door Officer defines. `POST /sub-agents/spawn` takes a prompt and an
optional cwd and model, and returns either the session key immediately or the
result if asked to wait. Verified both ways against the live server: the
synchronous call came back with the four words it was told to say, and the async
call returned in milliseconds and the agent had written its file within five
seconds.

The budget check comes BEFORE the spawn, and refuses with a 429 naming the window.
The windows belong to the Anthropic account and every `claude` on the machine
spends them, so an endpoint that could start work without asking would burn the
last of one and cut off the turn the owner is sitting in — a failure that lands on
somebody else's conversation, which is the worst place for it.

`confined`, and confined in FACT on the day it was added rather than ahead of
itself — the registry test's comment records that `chat` sat on that list for a day
before it was true. The identity comes from `chatIdentity` on the caller's token
and `member: { osUser, home }` goes to the sidecar, which is the mechanism chat
already runs under. There is no path in the endpoint that chooses a directory, so
there is nothing for a caller to point elsewhere. `member` is passed explicitly
because it is required-but-may-be-undefined on purpose: optional let a call site
forget it, and forgetting means a member's agent running as the owner.

Not a queue, not a supervisor, not a retry. One call starts one agent; a caller
that wants three tries writes three calls, because a retry in here would be a
policy nobody chose applied to work this endpoint cannot read.

Closes todo/sub-agents/an-api-endpoint-for-spawning-an-agent-with-a.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CLAUDE.md

@@ -207,7 +207,7 @@ ahead of everything, and it re-verifies the token itself so it covers routes tha
 - `permissions/registry.ts` — the single enumeration of what the platform can do, in five kinds:
   `core` (every account, not deniable), `app` (**the grantable surface**), `confined` (grantable, but
   only to an account that has a Linux user), `execution` and `admin` (owner only, and `execution` is
-  never grantable at any level). **20 entries as of 2026-08-23** — verified by `bun run docs:check`, which fails if this number drifts again: 5 core, 4 app, 3 confined, 4 execution, 4 admin. It said 27 for nine days.
+  never grantable at any level). **21 entries as of 2026-08-23** — verified by `bun run docs:check`, which fails if this number drifts again: 5 core, 4 app, 4 confined, 4 execution, 4 admin. It said 27 for nine days.
 - `permissions/authorize.ts` — resolves "may this account do this". Owner short-circuits first; every
   other answer is role grants plus core, with `execution`/`admin` stripped even if a row grants them,
   and `confined` stripped for an account with no `osUser`.