fix: run heartbeat LLM check when instructions aren't GitHub-only

[dimavedenyapin]

Problem

A heartbeat whose instructions are free text never got checked by the LLM — because one unrelated PR link elsewhere in the same file silenced the whole file.

runPreflightChecks() treats the presence of any GitHub URL in heartbeat.md as authority over the entire file. If gh api reports no new comments / reviews / CI failures / conflicts on that PR, it returns no_changes, and runHeartbeat() takes that as "nothing to do" and skips the LLM session entirely. Every non-GitHub instruction in the file is then silently never evaluated.

The reported task's heartbeat.md is 5.4 KB, and contains exactly one GitHub URL — buried in a findings note, not even a check:

## Latest Findings
- The PO matching aggregation wrapped `_id`, `issuerId`, ... Fix: https://github.com/peakflo/upload-functions/pull/9685.

## Heartbeat Checks
- [ ] Create `issuerId_1_scheduledDate_1` on `billing.bills`, then verify ...
- [ ] Recheck the next hourly Query Stats window ...
- [ ] Rewrite and test the AIExtractor company-alias aggregation ...
- [ ] Replace the repeated tax-embedding anti-join ...

None of the actual checks are GitHub checks. All of them were being skipped. Running the real file through the current code confirms it:

GITHUB_URLS_FOUND        = [{"owner":"peakflo","repo":"upload-functions","type":"pull","number":9685}]
OLD_CODE_TAKES_FAST_PATH = true
NEW_CODE_TAKES_FAST_PATH = false

heartbeat_logs for that task shows the fast path swallowing 8 consecutive runs over ~8 hours:

2026-07-31T02:04:14Z | ok | Pre-flight: no changes detected (LLM skipped)
2026-07-31T00:03:39Z | ok | Pre-flight: no changes detected (LLM skipped)
2026-07-30T22:02:44Z | ok | Pre-flight: no changes detected (LLM skipped)
...

(That log line is emitted only on no_changes, which is unreachable when zero URLs are extracted — so this is proof the file had the link, not an inference.)

The single escape hatch, requiresLlmCurrentStateChecks(), only matches /requested changes/, so it does not help.

Note: a heartbeat containing no GitHub URL at all already works correctly — pre-flight returns inconclusive and the LLM runs. The bug needs a URL to be present somewhere in the file.

Fix

Pre-flight may short-circuit only when every check line carries a GitHub URL it can verify with gh api (preflightCoversAllChecks). Anything else returns inconclusive, which routes to the LLM exactly as before.

To keep the cost optimisation for genuinely GitHub-only heartbeats, bodies of purely informational sections (## Latest Findings, ## Current Status, ## Notes, …) are not treated as checks — agents write those to record context, not instructions. That is also why the incidental PR link above no longer counts as coverage. Headings, horizontal rules, blockquotes and fenced code are skipped too.

The guard runs before any gh call, so mixed files no longer pay for API round-trips whose result would be discarded.

Test plan

• Regression test reproduces the production shape (quiet PR link + free-text check) — returned no_changes before, inconclusive now; verified failing against the unfixed code with expected 'no_changes' to be 'inconclusive'
• Verified against the actual 5.4 KB production heartbeat.md (see output above)
• Control tests confirm the fast path survives — a GitHub-only heartbeat with a quiet PR still returns no_changes, and a failed check-run still returns changes_detected
• gh is stubbed in tests, so pre-flight no longer hits the network
• pnpm test:main — 978 passed / 51 files
• pnpm typecheck clean; eslint clean on both files

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