feat(events): a failed step may say when to retry (MODULE_API 1.15.0)

A module's perform() may answer { ok: false, retry: true, retryAfterMs }
and the runner waits that long instead of the flat EVENT_STEP_RETRY_MS
(Rust PLAN_REDESIGNS §14.3.13, D371). Dangerous Treasures' warm-up is the
first user.

- dispatch.classify reads it on the retry shape only, clamped to 60 000 to
  1 800 000 ms; a value that is not a number is dropped and logged, and the
  step retries on the flat delay.
- It is one attempt of EVENT_STEP_MAX_ATTEMPTS and degrades the run like any
  retry. A run paused or cancelled in the wait is not picked up.
- Every step.retry log line now carries retryAt (and retryAfterMs when
  hinted); the run console reads "retrying at 20:10".
- MODULE_API 1.15.0, additions only; the engagement manifest is regenerated.
  Module-uo (^1.10.0) answers none of it and is unaffected.
- Test harness: resourcesDb.finishedRunsWithNothingLeft was never stubbed in
  eventRunner.test.js, so a tick that reached the cleanup sweep with a
  terminal run waited on the dead pool.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

client/test/eventAuthoring.test.js

@@ -347,6 +347,21 @@ test('the log lines a run produces all render as something', () => {
   }
 })
 
+test('a retry line says when it will run (MODULE_API 1.15.0), and an older line still reads', () => {
+  // Built from local parts so the assertion holds in any timezone the suite runs in.
+  const at = new Date(2026, 9, 15, 20, 10, 0)
+  const text = describeLogLine({
+    kind: 'step.retry',
+    detail: { action: 'rust.dt.start', attempt: 1, of: 3, error: 'not ready yet', retryAt: at.toISOString() },
+  })
+  assert.equal(text, 'rust.dt.start failed, attempt 1 of 3, retrying at 20:10: not ready yet')
+
+  const before = describeLogLine({ kind: 'step.retry', detail: { action: 'core.announce', attempt: 2, of: 3 } })
+  assert.equal(before, 'core.announce failed, attempt 2 of 3')
+  const junk = describeLogLine({ kind: 'step.retry', detail: { action: 'a', attempt: 1, of: 3, retryAt: 'soon' } })
+  assert.equal(junk, 'a failed, attempt 1 of 3', 'an unreadable time is left out, not shown as NaN')
+})
+
 // ── The one log line core did not compose (Phase 15) ──────────────────────
 
 test('a module detail line renders the module keys, not the kind id', () => {