Merge main into windows-support

Brings windows-support up to date with main (T-404/405/406, T-413–416,
T-421, the T-422 workspace-lifecycle epic, and the 2.4.0 release).

Conflict resolutions:
- terminal_pane.dart: keep the Windows PowerShell shell selection and
  main's workspace-cwd fix (T-381) together.
- tool_check.dart: accept main's deletion (dead, unreferenced code).
- CHANGELOG.md: keep both Unreleased sections.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/src/pty/native_pty.dart

@@ -451,6 +451,11 @@ class NativePty implements PtySession {
   void _reap() {
     if (_dead) return;
     _dead = true;
+    // The reader isolate sends EOF only after exiting its poll loop, so
+    // nothing touches the master fd anymore. Release it here — close()
+    // short-circuits on _dead, so skipping this leaks the fd and its pty
+    // device for the life of the app on every natural child exit (T-360).
+    _nativeClose(_fd);
     final s = calloc<ffi.Int32>();
     _waitpid(pid, s, _kWnohang);
     calloc.free(s);