Drop Deno from the agents and spawn child processes directly

.agents/memory/bot-agents-child-processes.md

@@ -0,0 +1,39 @@
+---
+description: Child processes use plain node:child_process spawn (explicit stdio, uid/gid, whole env); src/child.ts has exitCode (128+signo) and echo; no execFile maxBuffer
+---
+
+Every call site calls `spawn` from `node:child_process` itself, with
+everything explicit:
+
+- **`uid`/`gid`** of the profile for anything an agent profile runs (each
+  profile is its own UID, 20000+). Never drop them.
+- **`env`** is the whole environment the child gets (a sanitized one for
+  agents); nothing from the coordinator is merged in.
+- **`stdio`**: stdin is `"ignore"` so an agent CLI never waits on input
+  (only `codex login --with-api-key` pipes the token in). Output that is not
+  read is `"ignore"`; output that is read is `"pipe"` and streamed.
+- No `execFile`/`exec`: their `maxBuffer` (1 MiB) kills a chatty child. Read
+  piped streams incrementally instead.
+
+`src/child.ts` holds what the call sites share:
+
+- **`exitCode(child)`**: call it right after `spawn`. It settles on `exit`
+  (not `close`, which a daemonized grandchild can hold open), maps a signal to
+  `128 + signo` as a shell does, and rejects on a failed start. The rejection
+  is pre-caught so it is not reported as unhandled before the caller awaits it.
+- **`echo(stream, chunk)`**: writes and waits for `drain` when the buffer is
+  full, so echoing never outruns a slow reader.
+
+Tests use `spawnSync` for short commands.
+
+Other port details:
+
+- **`src/errors.ts`** `isNotFound` checks `ENOENT` (file) or `ESRCH` (process).
+- Temporary files are an exclusive `wx` create with mode `0600`.
+- `src/json.ts` holds type guards used instead of `as` casts on parsed JSON.
+- `process` and `Buffer` must come from `node:` imports:
+  `no-restricted-globals` in `scripts/project-lint.ts` enforces it
+  ([[lint-parity-never-shrinks]]).
+
+Related: how each agent CLI reports bad credentials is in
+[[agent-cli-auth-failures]].