fix(cron): eliminate double-announce and replace delivery polling with push-based flow (#39089)

* fix(cron): eliminate double-announce and replace delivery polling with push-based flow

- Set deliveryAttempted=true in announce early-return paths (active-subagent
  suppression and stale-interim suppression) so the heartbeat timer no longer
  fires a redundant enqueueSystemEvent fallback (double-announce bug).

- Refactor waitForDescendantSubagentSummary to use event-based agent.wait RPC
  calls instead of a 500ms busy-poll loop.  Each active descendant run is now
  awaited concurrently via Promise.allSettled, and only a short bounded grace
  period (5s) remains to capture the cron agent's post-orchestration synthesis.
  Eliminates O(n*timeoutMs/500ms) gateway calls and wasted wall-clock time.

- Add FAST_TEST_MODE (OPENCLAW_TEST_FAST=1) to subagent-followup.ts to keep
  the grace-period tests instant in CI.

- Add comprehensive tests for the new waitForDescendantSubagentSummary behaviour
  (push-based wait, error resilience, NO_REPLY handling, multi-descendant waits).

* fix: prep cron double-announce followup tests (#39089) (thanks @tyler6204)

CHANGELOG.md

@@ -628,6 +628,7 @@ Docs: https://docs.openclaw.ai
 
 ### Fixes
 
+- Cron/announce delivery: stop duplicate completion announces when cron early-return paths already handled delivery, and replace descendant followup polling with push-based waits so cron summaries arrive without the old busy-loop fallback. (#39089) Thanks @tyler6204.
 - Dashboard/macOS auth handling: switch the macOS “Open Dashboard” flow from query-string token injection to URL fragments, stop persisting Control UI gateway tokens in browser localStorage, and scrub legacy stored tokens on load. Thanks @JNX03 for reporting.
 - Models/provider config precedence: prefer exact `models.providers.<name>` matches before normalized provider aliases in embedded model resolution, preventing alias/canonical key collisions from applying the wrong provider `api`, `baseUrl`, or headers. (#35934) thanks @RealKai42.
 - Hooks/auth throttling: reject non-`POST` `/hooks/*` requests before auth-failure accounting so unsupported methods can no longer burn the hook auth lockout budget and block legitimate webhook delivery. Thanks @JNX03 for reporting.