refactor(hooks): tighten the hook-protocol contract surface

Implement the tighten-hook-protocol-contract RFC (moved to implemented/):

- HookDialect narrows to 'claude' | 'codex': the 'native' variant had zero
  producers (native plugins on the seams write no hook/* provenance), and the
  dialect is defined as the bridge that ran the hook.
- HookOutput.suppressOutput is gone: the codec parsed it and every path
  discarded it with no warn and no deferral — hook stdout never enters a
  transcript, so there is nothing to suppress.
- hook/result.durationMs is gone: durable timing telemetry with no reader
  that the snapshot normalizer had to scrub as replay noise. With no duration
  to measure, runHook loses its injected now clock and the single-field
  RunHookResult wrapper — it returns the HookOutput directly. The committed
  hook fixtures had the field stripped mechanically (field-only diff); the
  stdout goldens never carried it.
- The bridges' double-defaulted defaultTimeoutMs config knob is replaced by
  one reference-default constant, DEFAULT_HOOK_TIMEOUT_MS, exported from the
  lib's runner and applied inside runHook; per-hook timeoutSec stays the
  override surface.
- The hook/result semantics move into the lib that declares the event:
  HookResultRecord now carries the decoded HookOutput and appendHookResult
  derives the decision string (decision ?? stop-on-continue:false ?? pass)
  and the 500-char stderrSummary truncation; both bridges delete their
  byte-identical private copies. The snapshot suite passes against the
  existing goldens, proving the derived values are unchanged.
- Rider: BLOCKING_EXIT_CODE is codec-internal again (zero importers).

Amend the hook-protocol-lib and hook-snapshot-matrix RFCs to the new facts,
update the lib/bridge READMEs and the session.md event tables, and retarget
the affected unit tests (including new lib-level coverage of the derivation
rules).

packages/hooks/hooks-codex/tests/coverage.spec.ts

@@ -206,7 +206,7 @@ describe('hooks-codex coverage — decision mapping paths', () => {
     expect(res?.type === 'hook/result' && res.data.stderrSummary?.endsWith('…')).toBe(true)
   })
 
-  it('warns on a skipped async hook and a direct apply() defaults the timeout', async () => {
+  it('warns on a skipped async hook and a direct apply() (schema bypass) runs', async () => {
     const d = dir()
     const marker = join(d, 'ran')
     hooks(d, { UserPromptSubmit: [{ hooks: [
@@ -220,7 +220,7 @@ describe('hooks-codex coverage — decision mapping paths', () => {
     await ctx.plugin(ToolRegistry); await ctx.plugin(AgentRegistry); await ctx.plugin(AgentLoop, { agents: [] })
     await ctx.plugin(LocalBashExecutor, { timeoutMs: 10_000 })
     ctx.logger.warn = warn as never
-    // Direct apply (schema bypass) → defaultTimeoutMs ?? 600_000 + model ?? '' fallbacks.
+    // Direct apply (schema bypass) → the `model ?? ''` fallback is exercised.
     HooksCodex.apply(ctx, { configPath: join(d, 'hooks.json') })
     ctx.llm.registerAdapter(['mock'], adapter)
     const agent = ctx.agentLoop.create(AgentId('a1'), { model: 'mock' })