fix(subprocess): clean managed processes on host exit

packages/subprocess/subprocess-local/README.md

@@ -12,7 +12,8 @@ Local Service provider for the [`@deepseek-ai/dsh-subprocess`](../subprocess/REA
 - **Offset-based reads** — collect-mode readers return deltas in whole-stream byte coordinates; the service never holds a cursor, so consumer-owned cursors (the bash background read path) and full-stream re-reads coexist, before and after settlement.
 - **Executable lookup** — `resolveExecutable` checks absolute files or searches the scrubbed effective PATH with platform-aware executable extensions; relative paths containing separators are rejected at the seam, and relative PATH entries resolve from the host process cwd.
 - **Terminal-process ownership** — `spawnTerminal` allocates `node-pty`, bridges UTF-8 terminal text, inspects and signals the current foreground process group, and exposes one awaited termination operation that sweeps descendants before and after terminating the top-level shell. Each foreground inspection retains exact identities from the rooted tree; Linux also enumerates the POSIX session after its leader exits. A previously observed macOS descendant and any same-session Linux member therefore remain fenced after reparenting, while pid/start identity prevents cleanup from following PID reuse. The higher PTY backend owns prompt readiness, buffers, and model-facing operations.
-- **Terminate-and-join disposal** — the service retains live handles only so its own disposal can escalate every running tree and await its exit; settled and spawn-failed handles leave the live set on settlement.
+- **Terminate-and-join disposal** — the service retains live handles so its own disposal can escalate every running tree and await its exit; quiescent and spawn-failed handles leave the live set after whole-tree or terminal-session cleanup finishes.
+- **Synchronous host-exit finalization** — while the service effect is active, a Node `exit` listener force-terminates every ordinary tree and observable terminal session still in the same live sets. The local-only operations send POSIX SIGKILL to the managed group, run Windows `taskkill /T /F`, and synchronously signal captured/current terminal identities around the PTY root kill; they create no promise or timer, preserve the host's exit code and diagnostic, contain each target's failure, and do not claim quiescence. Normal disposal keeps the awaited graceful path above. See the [host-exit cleanup decision](../../../.agents/notes/implemented/bug-fix/2026-08-11-synchronous-subprocess-exit-cleanup.md).
 
 ## Model Experience
 
@@ -27,6 +28,7 @@ No direct invalidation; the named consumers own any request-prefix changes.
 - **Windows tree support is best-effort** — termination routes through `taskkill /PID <pid> /T /F` with all outcomes contained (absent tree, races, missing binary), and liveness falls back to the direct-child boundary.
 - **Terminal process inspection is Linux/macOS only** — the terminal primitive fails when its inspector has no supported platform implementation; Linux exact probes cover x64 and arm64, while macOS uses `ps` snapshots.
 - **A daemonized terminal descendant can still escape the observable boundary** — on macOS, a child that reparents before any foreground-inspection snapshot is no longer discoverable from the `node-pty` root; on Linux, a child that calls `setsid` leaves both the tree and owned terminal session. The local provider does not add a continuous process-table monitor.
+- **In-process cleanup requires a JavaScript-observable exit** — direct `process.exit()`, default uncaught exceptions, and default unhandled rejections emit Node's synchronous `exit` event. `SIGKILL`, fatal OOM, `process.abort()`, native crashes, power loss, and any failure that cannot run JavaScript require an external supervisor, container init, or equivalent OS owner.
 - **The credential scrub is a name heuristic** — `*KEY*`/`*PASSWORD*`/`*SECRET*`/`*TOKEN*` only; differently-named secrets (e.g. `*PASSPHRASE*`) pass through, and a whitelist for over-scrubbed vars is noted future work.
 - **Completed spill files are not deleted** — bounded full-output recovery files (and the private per-process spill dir) accumulate under the OS tmpdir until something external cleans them; oversize incomplete spills are discarded and deletion is attempted immediately, but a cleanup failure can leave a bounded file behind.