Fixes#87438.
Bound unset heartbeat run timeouts so background heartbeat turns no longer inherit the built-in 48-hour interactive agent default. Timeout precedence is explicit heartbeat timeout, explicit global agent timeout, then heartbeat cadence capped at 600 seconds.
Verification:
- git diff --check
- Testbox tbx_01kstna69zvznn4fq7zrqr04a1: corepack pnpm test src/infra/heartbeat-runner.model-override.test.ts -- --reporter=verbose passed 13 tests
- Direct node --import tsx runtime probe verified 300s, 600s, 60s, and 45s timeout precedence cases
- Autoreview clean
Known CI state:
- PR CI run 26661465248 has failures matching latest main CI run 26661386468 at a7820b2f54; failures are outside this six-file heartbeat/docs diff.
31169ff3b4
