Replace ad-hoc cron Scheduler with chained-timeout helper

[Brutus5000]

Summary

• New tiny helpers in src/backend/cron-jobs/: scheduleRepeating (chained setTimeout, can't overlap, returns a .stop() handle) and warmAll (collects per-action failures via Promise.allSettled, logs each, then throws so the scheduler-level log records the failure).
• Single CACHE_WARM_INTERVAL_MS constant in constants.js replaces the magic 60 * 59 * 1000 that was duplicated in each crawler. Comment explains the relationship to the 60-minute service cache TTL.
• The three crawlers (leaderboard, wordpress, clan) shrink to ~15 lines each — just a list of named warmup actions.
• AppKernel.startCronJobs now registers SIGTERM/SIGINT handlers that call .stop() on every scheduler, so the pending timer is cleared on shutdown (no leaked timers under nodemon or Docker stop).
• Deletes the EventEmitter-based services/Scheduler.js (22 lines wrapping setInterval for no real benefit).

Net diff: +116 / -196 across 8 files; cron-jobs/ directory goes from ~190 LOC to ~110.

Why

The previous Scheduler class added indirection without value, and each crawler reimplemented the same boilerplate (per-call success/error handlers, magic interval constant, top-level catch). Three concrete bugs/risks the cleanup also fixes:

1. setInterval could schedule a second warmup before the previous one finished — now impossible because the next timer is only set in finally after the run completes.
2. No clean shutdown — timer handles were never cleared on signal, so nodemon restarts and Docker stop would leak callbacks until the process exited.
3. Per-action failure isolation was copy-pasted into every crawler; now lives in one helper and behaves consistently.

This deliberately does not introduce node-cron or a job queue (BullMQ etc.) — neither would solve a real problem here, and both would add deps.

Test plan

• yarn lint clean
• yarn test — 71/71 (tests don't exercise startCronJobs, but they do boot AppKernel and would catch import-level breakage)
• Manual: deploy to test env, confirm [scheduler] leaderboard-cache ok in Xms (or failed) lines appear at startup and roughly every 59 minutes
• Manual: docker stop the running container, confirm the process exits cleanly (no lingering timer warnings)

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Improved shutdown behavior: background tasks now properly stop when the application receives shutdown signals.

• Refactor

  • Optimized cache warming operations to run concurrently instead of sequentially, improving overall performance.
  • Introduced configurable cache refresh intervals with intelligent timing designed to refresh cached data before expiry.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 1ecff770-992e-4f39-b575-2198ec6c5bbb

📥 Commits

Reviewing files that changed from the base of the PR and between eace251 and 78b6531.

📒 Files selected for processing (8)

• src/backend/AppKernel.js
• src/backend/cron-jobs/clanCacheCrawler.js
• src/backend/cron-jobs/constants.js
• src/backend/cron-jobs/leaderboardCacheCrawler.js
• src/backend/cron-jobs/scheduleRepeating.js
• src/backend/cron-jobs/warmAll.js
• src/backend/cron-jobs/wordpressCacheCrawler.js
• src/backend/services/Scheduler.js

💤 Files with no reviewable changes (1)

• src/backend/services/Scheduler.js

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📝 Walkthrough

Walkthrough

The PR replaces a monolithic EventEmitter-based Scheduler class with composable utilities: scheduleRepeating for interval-based async task scheduling with logging, and warmAll for concurrent cache-warming with error aggregation. All three cache crawlers (clan, leaderboard, WordPress) are refactored to use these utilities with a shared interval constant. AppKernel now gracefully stops all schedulers on termination signals.

Changes

Scheduler Replacement and Graceful Shutdown

Layer / File(s)	Summary
Core scheduling and warming utilities src/backend/cron-jobs/scheduleRepeating.js, src/backend/cron-jobs/warmAll.js, src/backend/cron-jobs/constants.js	New scheduleRepeating async scheduler executes functions on intervals with timing and error logs; new warmAll concurrently warms caches via Promise.allSettled and aggregates failures; shared CACHE_WARM_INTERVAL_MS constant (59 minutes) undershoots cache TTL.
Refactor cache crawlers to new scheduler pattern src/backend/cron-jobs/clanCacheCrawler.js, src/backend/cron-jobs/leaderboardCacheCrawler.js, src/backend/cron-jobs/wordpressCacheCrawler.js	clanCacheCrawler, leaderboardCacheCrawler, and wordpressCacheCrawler all migrate from manual Scheduler construction to scheduleRepeating with warmAll delegation; removes per-entry try/catch logging and simplifies to data-driven warmup functions.
Graceful shutdown on termination signals src/backend/AppKernel.js	startCronJobs() registers SIGTERM/SIGINT handlers that iterate this.schedulers and call stop() on each, preventing orphaned timeouts after process exit.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 The old Scheduler class takes its final bow,
New utilities dance in harmony now,
scheduleRepeating and warmAll play their part,
While caches refresh with a synchronized heart,
And when signals arrive, the shutdown's so clean! 🌿

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: replacing a custom EventEmitter-based Scheduler with a simpler chained-timeout helper pattern.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/scheduler-cleanup

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