* feat: skip heartbeat API calls when HEARTBEAT.md is effectively empty
- Added isHeartbeatContentEffectivelyEmpty() to detect files with only headers/comments
- Modified runHeartbeatOnce() to check HEARTBEAT.md content before polling the LLM
- Returns early with 'empty-heartbeat-file' reason when no actionable tasks exist
- Preserves existing behavior when file is missing (lets LLM decide)
- Added comprehensive test coverage for empty file detection
- Saves API calls/costs when heartbeat file has no meaningful content
* chore: update HEARTBEAT.md template to be effectively empty by default
Changed instruction text to comment format so new workspaces benefit from
heartbeat optimization immediately. Users still get clear guidance on usage.
* fix: only treat markdown headers (# followed by space) as comments, not #TODO etc
* refactor: simplify regex per code review suggestion
* docs: clarify heartbeat empty file behavior (#1535) (thanks @JustYannicc)
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Co-authored-by: Peter Steinberger <steipete@gmail.com>
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