feat(#772): adopt stable Codex hook events + commandWindows for Windows parity (#827)

* feat(#772): adopt stable Codex hook events + commandWindows for Windows parity

Register three new stable Codex hook events (SubagentStart, Stop,
PostToolUse) wired to gsd-context-monitor.js so Codex installs get
the same context-headroom tracking at subagent and session boundaries
that Claude/Qwen already have.

Add commandWindows field to the SessionStart hook entry on Windows so
Codex uses the .cmd shim directly (Git Bash/MSYS cannot POSIX-exec
node.exe). commandWindows is only emitted on win32; POSIX is unchanged.

Refactor reconcileCodexHooksJsonSessionStart into a generic
reconcileCodexHooksJsonEvent so any event name can be reconciled with
the same dedup/preserve-user-entries logic.

Add gsd-context-monitor.js and .cmd to MANAGED_HOOK_COMMAND_BASENAMES
_BY_SURFACE so idempotent re-runs de-duplicate entries correctly.

30 new tests covering: export surface, event registration for each of
the three events, commandWindows parity (POSIX vs win32), idempotency,
uninstall, and user-entry preservation.

Closes #772

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix(#772): windows path normalization + docs-lint

- Normalize scriptPath backslashes to forward slashes in
  ensureCodexHooksJsonEvent and ensureCodexHooksJsonSessionStart so that
  isManagedHookCommand can match stored commands against configDir on
  Windows CI runners. path.resolve returns backslash paths on Windows,
  but when platform is not 'win32' (e.g. platform:'linux' in tests),
  projectManagedHookCommand skips normalization — producing a mismatch
  that breaks idempotency deduplication (the same hook entry appended
  twice on re-register). Forward-slash paths are always valid in both
  Node.js and Codex, so the normalization is safe for all platforms.
- Fix changeset pr: 0 → 827 to resolve fail_malformed_fragment.
- Add Codex hook coverage table to docs/how-to/install-on-your-runtime.md
  documenting the SubagentStart/Stop/PostToolUse events + commandWindows
  Windows-parity field added by this enhancement.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/shell-command-projection.cts

@@ -181,6 +181,10 @@ const MANAGED_HOOK_COMMAND_BASENAMES_BY_SURFACE: Record<string, Set<string>> = {
     // reconcileCodexHooksJsonSessionStart can replace stale node-runner commands
     // with the .cmd shim on reinstall (and vice-versa on cross-platform moves).
     'gsd-check-update.cmd',
+    // #772: context-monitor is now registered for Codex SubagentStart/Stop/PostToolUse.
+    'gsd-context-monitor.js',
+    // #772: Windows .cmd shim for gsd-context-monitor — same #3426 pattern.
+    'gsd-context-monitor.cmd',
   ]),
 };