#6522: fix(cron): deliver original message when agent response is heartbeat-only

## Summary Fixes #6341 — When a cron job with `deliver: true` runs and the agent response is filtered as heartbeat-only (e.g. `HEARTBEAT_OK`), the scheduler silently returns `status: "ok"` without delivering anything. The user never receives their reminder. ## Root Cause In `src/cron/isolated-agent/run.ts`, when `isHeartbeatOnlyResponse()` returns true, `skipHeartbeatDelivery` is set and the entire delivery block is bypassed. The original `params.message` (the reminder text from the job config) is never used as a fallback — it's simply discarded. ## Fix When heartbeat filtering triggers and the job has a non-empty original message, substitute the original message as the delivery payload instead of skipping delivery entirely: ```typescript if (skipHeartbeatDelivery && originalMessage) { effectivePayloads = [{ text: originalMessage }]; skipHeartbeatDelivery = false; } ``` This reuses the existing delivery block (channel routing, error handling, `bestEffortDeliver` logic) with zero duplication. When the original message is empty/whitespace, delivery is still skipped (no blank messages). ## What's NOT changed - `helpers.ts` — `isHeartbeatOnlyResponse()` works correctly, no changes - `delivery-target.ts` / `targets.ts` — separate issue (#6340) - No other channels, no config changes, no type changes - Heartbeat filtering still works for responses with substantial content (existing test unchanged) ## Testing - [x] Updated `"skips delivery when response is exactly HEARTBEAT_OK"` → now expects fallback delivery of original message - [x] Updated `"skips delivery when response has HEARTBEAT_OK with short padding"` → same - [x] Added `"skips delivery when heartbeat response and original message is empty"` edge case - [x] Existing `"delivers when response has HEARTBEAT_OK but also substantial content"` still passes (no change) - [x] All 26 cron tests pass (3 test files) - [x] `pnpm tsgo` — no type errors - [x] `pnpm lint` — 0 warnings, 0 errors - [x] `oxfmt --check` — clean ## AI Disclosure Built with Claude (AI-assisted). Fully tested locally. I understand what the code does. **Diff: 2 files, +67 / -9 lines.** <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR updates the cron isolated-agent runner to avoid silently skipping delivery when the agent’s response is filtered as heartbeat-only (e.g., `HEARTBEAT_OK`) and `deliver: true` is set. In `src/cron/isolated-agent/run.ts`, it introduces an `effectivePayloads` fallback that substitutes the original cron job message (`params.message.trim()`) as the delivery payload when heartbeat filtering would otherwise skip delivery, preserving the existing outbound delivery pathway. It also updates cron isolated-agent tests to assert this new behavior (deliver the original message on heartbeat-only responses) and adds an edge-case test to ensure delivery still skips when the original message is empty/whitespace. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk. - The change is narrowly scoped to cron delivery behavior when responses are heartbeat-only, reuses existing delivery plumbing, and is covered by updated and new tests for the fallback and whitespace edge case. No broader routing or type changes are introduced. - No files require special attention <!-- greptile_other_comments_section --> <!-- /greptile_comment -->