restore hook/result durationMs — review keeps wall-clock audit timing durable

Reverses item 3 of the tighten-hook-protocol-contract RFC per review:
a persistence log is written for future readers, and hook wall-clock
runtime is audit signal (which hook made a turn slow). runHook keeps
its injected now clock and RunHookResult wrapper, the bridges pass the
measured duration through HookResultRecord, the snapshot normalizer
keeps its replay scrub, and the hook fixtures carry the field again.
The RFC records the reversal; the other three prunes stand.

examples/acp-agent/tests/snapshot-normalize.spec.ts

@@ -91,14 +91,20 @@ describe('normalizeSessionLog', () => {
     expect(out).toContain('{{sessionId}}')
   })
 
-  it('leaves event data fields untouched beyond the time zeroing (no per-event field scrubs)', () => {
+  it('zeroes a hook/result durationMs (run-to-run noise) but keeps its decision', () => {
     const ev = JSON.stringify({
       type: 'hook/result', seq: 2, time: 5,
-      data: { turn: 1, point: 'UserPromptSubmit', handlerId: 'h', decision: 'block', exitCode: 2 },
+      data: { turn: 1, point: 'UserPromptSubmit', handlerId: 'h', decision: 'block', exitCode: 2, durationMs: 37 },
     })
     const out = normalizeSessionLog(`${header({})}\n${ev}\n`, ctx)
-    expect(out).toContain('"decision":"block"')
-    expect(out).toContain('"exitCode":2')
-    expect(out).toContain('"time":0')
+    expect(out).toContain('"durationMs":0')
+    expect(out).not.toContain('37')
+    expect(out).toContain('"decision":"block"') // the decision is the behavior — kept
+  })
+
+  it('leaves a non-hook event durationMs untouched (only hook/result is scrubbed)', () => {
+    const ev = JSON.stringify({ type: 'tool/result', seq: 2, time: 5, data: { durationMs: 88 } })
+    const out = normalizeSessionLog(`${header({})}\n${ev}\n`, ctx)
+    expect(out).toContain('"durationMs":88')
   })
 })