fix(core): resolve spawn completion on exit, not only close (Windows detached-child hang)

[Hona]

Summary

Fix shell commands hanging after their main process exits while a child still holds stdout/stderr open.

Fix

• Track process exited separately from stream/group closed.
• exitCode / isRunning resolve on exited; kill escalation (forceKillAfter) waits on closed so resistant descendants are still SIGKILLed.
• ShellTool completion = joining the output reader (drains to EOF). For a normal command this returns the instant the streams end: full output, no wall-clock delay, same backpressure-synced guarantee as before. A detached child can hold the pipe open forever, so an idle watcher that resets on every chunk bounds only that case -- a command still producing output is never cut off.

Why no temp file / no fixed drain

close only fires once every holder of the stdio write-end closes; a detached grandchild that inherited the pipe keeps it open, so close never comes. We cannot control the grandchild's stdio, so completion must key off process exit. "Exited" does not mean "fully read" -- a small produced-but-unconsumed backlog can remain, which is why we join the reader. A fixed-duration drain truncates that backlog for slow consumers; the idle-reset watcher does not.

Tests

• Detached child inheriting stdio no longer blocks exitCode (core spawner).
• POSIX kill escalation still SIGKILLs a SIGTERM-resistant descendant after the parent exits, including non-zero parent exit (core spawner).
• 1MB of fast output with delayed per-chunk metadata is fully captured after exit (shell tool).
• A command that leaves a detached child holding stdio open returns promptly via the idle drain instead of hanging on the pipe or the command timeout (shell tool, POSIX).
• Windows shell suite: 92/92.

Closes #24731
Closes #24784
Closes #20902
Closes #29822
Closes #25038
Closes #28697
Closes #25938

Refs #28654
Refs #22012

[Copilot]

Pull request overview

Fixes a Windows hang in the shell tool when a command spawns a detached child that inherits stdio (e.g. playwright-cli). The CrossSpawnSpawner previously completed only on the child's "close" event, which can be delayed indefinitely if a detached child keeps the parent's stdio pipes open. The fix completes the exit Deferred on whichever of "exit" or "close" fires first, while preserving the "close" listener as a backstop for the ENOENT path where cross-spawn never emits "exit".

Changes:

• Resolve the spawn completion Deferred in the "exit" handler in addition to the existing "close" handler, with end/exit guards so the value is consistent regardless of order.
• Added an explanatory comment documenting why both events are needed.
• Added a regression test (using fx.live) that spawns a detached daemon inheriting stdio and asserts exitCode resolves within 5s, reaping the daemon afterward.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
packages/core/src/cross-spawn-spawner.ts	Complete on first of exit/close; keep close as ENOENT backstop.
packages/core/test/effect/cross-spawn-spawner.test.ts	New regression test for detached child stdio inheritance (#24731); trailing blank lines added.

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