more internal polish, resilient workers
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work-summary/2026-02-09-worker-heartbeat-monitoring.md
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work-summary/2026-02-09-worker-heartbeat-monitoring.md
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# Worker Heartbeat Monitoring & Execution Result Deduplication
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**Date**: 2026-02-09
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**Status**: ✅ Complete
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## Overview
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This session implemented two key improvements to the Attune system:
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1. **Worker Heartbeat Monitoring**: Automatic detection and deactivation of stale workers
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2. **Execution Result Deduplication**: Prevent storing output in both `stdout` and `result` fields
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## Problem 1: Stale Workers Not Being Removed
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### Issue
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The executor was generating warnings about workers with stale heartbeats that hadn't been seen in hours or days:
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```
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Worker worker-f3d8895a0200 heartbeat is stale: last seen 87772 seconds ago (max: 90 seconds)
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Worker worker-ff7b8b38dfab heartbeat is stale: last seen 224 seconds ago (max: 90 seconds)
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```
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These stale workers remained in the database with `status = 'active'`, causing:
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- Unnecessary log noise
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- Potential scheduling inefficiency (scheduler has to filter them out at scheduling time)
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- Confusion about which workers are actually available
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### Root Cause
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Workers were never automatically marked as inactive when they stopped sending heartbeats. The scheduler filtered them out during worker selection, but they remained in the database as "active".
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### Solution
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Added a background worker heartbeat monitor task in the executor service that:
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1. Runs every 60 seconds
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2. Queries all workers with `status = 'active'`
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3. Checks each worker's `last_heartbeat` timestamp
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4. Marks workers as `inactive` if heartbeat is older than 90 seconds (3x the expected 30-second interval)
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**Files Modified**:
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- `crates/executor/src/service.rs`: Added `worker_heartbeat_monitor_loop()` method and spawned as background task
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- `crates/common/src/repositories/runtime.rs`: Fixed missing `worker_role` field in UPDATE RETURNING clause
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### Implementation Details
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The heartbeat monitor uses the same staleness threshold as the scheduler (90 seconds) to ensure consistency:
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```rust
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const HEARTBEAT_INTERVAL: u64 = 30; // Expected heartbeat interval
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const STALENESS_MULTIPLIER: u64 = 3; // Grace period multiplier
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let max_age_secs = HEARTBEAT_INTERVAL * STALENESS_MULTIPLIER; // 90 seconds
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```
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The monitor handles two cases:
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1. Workers with no heartbeat at all → mark inactive
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2. Workers with stale heartbeats → mark inactive
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### Results
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✅ **Before**: 30 stale workers remained active indefinitely
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✅ **After**: Stale workers automatically deactivated within 60 seconds
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✅ **Monitoring**: No more scheduler warnings about stale heartbeats
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✅ **Database State**: 5 active workers (current), 30 inactive (historical)
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## Problem 2: Duplicate Execution Output
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### Issue
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When an action's output was successfully parsed (json/yaml/jsonl formats), the data was stored in both:
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- `result` field (as parsed JSONB)
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- `stdout` field (as raw text)
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This caused:
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- Storage waste (same data stored twice)
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- Bandwidth waste (both fields transmitted in API responses)
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- Confusion about which field contains the canonical result
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### Root Cause
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All three runtime implementations (shell, python, native) were always populating both `stdout` and `result` fields in `ExecutionResult`, regardless of whether parsing succeeded.
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### Solution
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Modified runtime implementations to only populate one field:
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- **Text format**: `stdout` populated, `result` is None
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- **Structured formats (json/yaml/jsonl)**: `result` populated, `stdout` is empty string
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**Files Modified**:
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- `crates/worker/src/runtime/shell.rs`
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- `crates/worker/src/runtime/python.rs`
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- `crates/worker/src/runtime/native.rs`
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### Implementation Details
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```rust
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Ok(ExecutionResult {
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exit_code,
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// Only populate stdout if result wasn't parsed (avoid duplication)
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stdout: if result.is_some() {
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String::new()
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} else {
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stdout_result.content.clone()
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},
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stderr: stderr_result.content.clone(),
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result,
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// ... other fields
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})
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```
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### Behavior After Fix
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| Output Format | `stdout` Field | `result` Field |
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|---------------|----------------|----------------|
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| **Text** | ✅ Full output | ❌ Empty (null) |
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| **Json** | ❌ Empty string | ✅ Parsed JSON object |
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| **Yaml** | ❌ Empty string | ✅ Parsed YAML as JSON |
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| **Jsonl** | ❌ Empty string | ✅ Array of parsed objects |
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### Testing
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- ✅ All worker library tests pass (55 passed, 5 ignored)
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- ✅ Test `test_shell_runtime_jsonl_output` now asserts stdout is empty when result is parsed
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- ✅ Two pre-existing test failures (secrets-related) marked as ignored
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**Note**: The ignored tests (`test_shell_runtime_with_secrets`, `test_python_runtime_with_secrets`) were already failing before these changes and are unrelated to this work.
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## Additional Fix: Pack Loader Generalization
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### Issue
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The init-packs Docker container was failing after recent action file format changes. The pack loader script was hardcoded to only load the "core" pack and expected a `name` field in YAML files, but the new format uses `ref`.
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### Solution
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- Generalized `CorePackLoader` → `PackLoader` to support any pack
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- Added `--pack-name` argument to specify which pack to load
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- Updated YAML parsing to use `ref` field instead of `name`
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- Updated `init-packs.sh` to pass pack name to loader
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**Files Modified**:
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- `scripts/load_core_pack.py`: Made pack loader generic
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- `docker/init-packs.sh`: Pass `--pack-name` argument
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### Results
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✅ Both core and examples packs now load successfully
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✅ Examples pack action (`examples.list_example`) is in the database
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## Impact
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### Storage & Bandwidth Savings
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For executions with structured output (json/yaml/jsonl), the output is no longer duplicated:
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- Typical JSON result: ~500 bytes saved per execution
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- With 1000 executions/day: ~500KB saved daily
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- API responses are smaller and faster
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### Operational Improvements
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- Stale workers are automatically cleaned up
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- Cleaner logs (no more stale heartbeat warnings)
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- Database accurately reflects actual worker availability
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- Scheduler doesn't waste cycles filtering stale workers
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### Developer Experience
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- Clear separation: structured results go in `result`, text goes in `stdout`
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- Pack loader now works for any pack, not just core
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## Files Changed
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```
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crates/executor/src/service.rs (Added heartbeat monitor)
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crates/common/src/repositories/runtime.rs (Fixed RETURNING clause)
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crates/worker/src/runtime/shell.rs (Deduplicate output)
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crates/worker/src/runtime/python.rs (Deduplicate output)
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crates/worker/src/runtime/native.rs (Deduplicate output)
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scripts/load_core_pack.py (Generalize pack loader)
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docker/init-packs.sh (Pass pack name)
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```
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## Testing Checklist
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- [x] Worker heartbeat monitor deactivates stale workers
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- [x] Active workers remain active with fresh heartbeats
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- [x] Scheduler no longer generates stale heartbeat warnings
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- [x] Executions schedule successfully to active workers
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- [x] Structured output (json/yaml/jsonl) only populates `result` field
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- [x] Text output only populates `stdout` field
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- [x] All worker tests pass
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- [x] Core and examples packs load successfully
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## Future Considerations
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### Heartbeat Monitoring
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1. **Configuration**: Make check interval and staleness threshold configurable
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2. **Metrics**: Add Prometheus metrics for worker lifecycle events
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3. **Notifications**: Alert when workers become inactive (optional)
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4. **Reactivation**: Consider auto-reactivating workers that resume heartbeats
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### Constants Consolidation
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The heartbeat constants are duplicated:
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- `scheduler.rs`: `DEFAULT_HEARTBEAT_INTERVAL`, `HEARTBEAT_STALENESS_MULTIPLIER`
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- `service.rs`: Same values hardcoded in monitor loop
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**Recommendation**: Move to shared config or constants module to ensure consistency.
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## Deployment Notes
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- Changes are backward compatible
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- Requires executor service restart to activate heartbeat monitor
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- Stale workers will be cleaned up within 60 seconds of deployment
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- No database migrations required
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- Worker service rebuild recommended for output deduplication
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