fix(#2289): context-monitor emits injection envelope only for supported events (#2324)

* fix(#2289): context-monitor emits injection envelope only for supported events

gsd-context-monitor is wired to Codex Stop/SubagentStart/SubagentStop/PreCompact
(#772), but it emitted a hookSpecificOutput.additionalContext envelope for every
event. Codex's Stop schema rejects that shape ("hook returned invalid stop hook
JSON output") exactly when context is low.

Use a positive allowlist: emit only for context-injection events (PostToolUse,
AfterTool, and the pre-existing Gemini missing-name fallback); exit 0 silently
for Stop and every other event. Debounce and critical-session bookkeeping still
run on silenced events. Behavioral regression tests drive the real hook.

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

* docs(#2289): backfill PR number 2324 into changeset

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

* test(#2285): de-flake per-plan use_worktree property test on duplicate briefs

The fast-check property in claude-orchestration.test.cjs located each plan's
agent() call via indexOf on the brief, but only plan IDs were unique — briefs
could collide (fast-check shrinks toward short strings). On a colliding seed the
lookup found the first duplicate's line and misattributed its isolation, failing
"use_worktree:true must carry isolation" intermittently (surfaced on macOS CI).
emitWorkflowScript is correct for duplicate briefs (verified); suffix the unique
id onto each agent() label so the test probe is unambiguous.

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

---------

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

tests/fixtures/golden-install-parity/opencode.json

@@ -385,7 +385,7 @@
   "hooks/gsd-check-update-worker.js": "385fb7c67810baf6",
   "hooks/gsd-check-update.js": "4549451414ffa7d7",
   "hooks/gsd-config-reload.js": "96546e0e8bb47904",
-  "hooks/gsd-context-monitor.js": "7a9787868a39b76d",
+  "hooks/gsd-context-monitor.js": "91ce47cd2dc3bbe8",
   "hooks/gsd-cursor-post-tool.js": "9168e0a09de1972a",
   "hooks/gsd-cursor-pre-tool.js": "873998b25e308c29",
   "hooks/gsd-cursor-session-start.js": "9b2e6f4f0c405375",