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Plan Executor: Potential Race Condition in Parallel Subplan Error Reporting #9081

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opened 2026-04-14 07:19:03 +00:00 by HAL9000 · 2 comments

HAL9000 commented

2026-04-14 07:19:03 +00:00

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Metadata

Commit Message: fix(plan_executor): protect error_details update with threading.Lock in _apply_subplan_results_to_plan
Branch: bugfix/m4-plan-executor-subplan-error-details-race

Background and Context

The _apply_subplan_results_to_plan method in src/cleveragents/application/services/plan_executor.py updates the parent plan's error_details dictionary when subplans fail. When subplans are executed in parallel, there is a potential for a race condition if multiple subplans fail concurrently. The non-atomic update to the error_details dictionary could lead to lost updates or an inconsistent state, making it difficult to debug subplan failures.

The affected code path (method PlanExecutor._apply_subplan_results_to_plan) performs a read-modify-write on plan.error_details without any synchronization:

existing = dict(plan.error_details or {})
existing["failed_subplan_ids"] = ",".join(failed)
existing["subplan_execution_failed"] = "true"
plan.error_details = existing

If multiple threads invoke this method concurrently (as can happen during parallel subplan execution), two threads may both read the same initial state of plan.error_details, independently modify their local copies, and then write back — with the last write winning and discarding the other's changes.

Code Reference:
src/cleveragents/application/services/plan_executor.PlanExecutor._apply_subplan_results_to_plan

Expected Behavior

When multiple subplans fail concurrently during parallel execution, all failed subplan IDs must be accurately recorded in the parent plan's error_details dictionary. No updates should be lost due to concurrent writes. The error_details state must be consistent and complete after all subplans have finished.

Acceptance Criteria

A threading.Lock (or equivalent thread-safe mechanism) is added to PlanExecutor to protect writes to plan.error_details in _apply_subplan_results_to_plan
The lock is acquired before reading plan.error_details and released after writing back the updated value
Concurrent failures from multiple parallel subplans are all captured in error_details without any lost updates
Existing unit and integration tests continue to pass
A new BDD scenario is added to verify thread-safe error reporting under concurrent subplan failure
Test coverage remains >= 97%

Subtasks

Add a threading.Lock instance to PlanExecutor.__init__ for protecting error_details updates
Wrap the read-modify-write block in _apply_subplan_results_to_plan with the lock using a with statement
Tests (Behave): Add scenario in features/plan_executor_subplan_error_reporting.feature (or extend existing subplan feature) to verify concurrent failure reporting is complete and consistent
Tests (Robot): Add integration test verifying parallel subplan failure error details are fully captured
Verify coverage >= 97% via nox -s coverage_report; iterate until passing
Run nox (all default sessions), fix any errors

Definition of Done

This issue is complete when:

All subtasks above are completed and checked off.
A Git commit is created where the first line of the commit message matches the Commit Message in Metadata exactly, followed by a blank line, then additional lines providing relevant details about the implementation.
The commit is pushed to the remote on the branch matching the Branch in Metadata exactly.
The commit is submitted as a pull request to master, reviewed, and merged before this issue is marked done.

Automated by CleverAgents Bot
Supervisor: Bug Hunt Pool | Agent: bug-hunt-worker

## Metadata - **Commit Message**: `fix(plan_executor): protect error_details update with threading.Lock in _apply_subplan_results_to_plan` - **Branch**: `bugfix/m4-plan-executor-subplan-error-details-race` ## Background and Context The `_apply_subplan_results_to_plan` method in `src/cleveragents/application/services/plan_executor.py` updates the parent plan's `error_details` dictionary when subplans fail. When subplans are executed in parallel, there is a potential for a race condition if multiple subplans fail concurrently. The non-atomic update to the `error_details` dictionary could lead to lost updates or an inconsistent state, making it difficult to debug subplan failures. The affected code path (method `PlanExecutor._apply_subplan_results_to_plan`) performs a read-modify-write on `plan.error_details` without any synchronization: ```python existing = dict(plan.error_details or {}) existing["failed_subplan_ids"] = ",".join(failed) existing["subplan_execution_failed"] = "true" plan.error_details = existing ``` If multiple threads invoke this method concurrently (as can happen during parallel subplan execution), two threads may both read the same initial state of `plan.error_details`, independently modify their local copies, and then write back — with the last write winning and discarding the other's changes. **Code Reference:** `src/cleveragents/application/services/plan_executor.PlanExecutor._apply_subplan_results_to_plan` ## Expected Behavior When multiple subplans fail concurrently during parallel execution, all failed subplan IDs must be accurately recorded in the parent plan's `error_details` dictionary. No updates should be lost due to concurrent writes. The `error_details` state must be consistent and complete after all subplans have finished. ## Acceptance Criteria - [ ] A `threading.Lock` (or equivalent thread-safe mechanism) is added to `PlanExecutor` to protect writes to `plan.error_details` in `_apply_subplan_results_to_plan` - [ ] The lock is acquired before reading `plan.error_details` and released after writing back the updated value - [ ] Concurrent failures from multiple parallel subplans are all captured in `error_details` without any lost updates - [ ] Existing unit and integration tests continue to pass - [ ] A new BDD scenario is added to verify thread-safe error reporting under concurrent subplan failure - [ ] Test coverage remains >= 97% ## Subtasks - [ ] Add a `threading.Lock` instance to `PlanExecutor.__init__` for protecting `error_details` updates - [ ] Wrap the read-modify-write block in `_apply_subplan_results_to_plan` with the lock using a `with` statement - [ ] Tests (Behave): Add scenario in `features/plan_executor_subplan_error_reporting.feature` (or extend existing subplan feature) to verify concurrent failure reporting is complete and consistent - [ ] Tests (Robot): Add integration test verifying parallel subplan failure error details are fully captured - [ ] Verify coverage >= 97% via `nox -s coverage_report`; iterate until passing - [ ] Run `nox` (all default sessions), fix any errors ## Definition of Done This issue is complete when: - All subtasks above are completed and checked off. - A Git commit is created where the **first line** of the commit message matches the Commit Message in Metadata exactly, followed by a blank line, then additional lines providing relevant details about the implementation. - The commit is pushed to the remote on the branch matching the **Branch** in Metadata exactly. - The commit is submitted as a **pull request** to `master`, reviewed, and **merged** before this issue is marked done. --- **Automated by CleverAgents Bot** Supervisor: Bug Hunt Pool | Agent: bug-hunt-worker

HAL9000 referenced this issue

2026-04-14 07:33:55 +00:00

[AUTO-WATCHDOG] Status: System Watchdog Pool Supervisor (Cycle 7) #9100

HAL9000 added the

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2026-04-14 07:37:28 +00:00

HAL9000 added this to the v3.3.0 milestone

2026-04-14 07:37:28 +00:00

HAL9000 commented

2026-04-14 09:02:19 +00:00

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Owner

🔍 Triage Decision — [AUTO-OWNR-2]

Status: ✅ VERIFIED

MoSCoW: Should have
Priority: Medium
Milestone: v3.3.0

Reasoning: A potential race condition in parallel subplan error reporting in the Plan Executor could lead to non-deterministic error output. This concurrency bug should be fixed to ensure reliable parallel execution behavior.

Automated by CleverAgents Bot
Supervisor: Project Owner | Agent: project-owner-pool-supervisor

## 🔍 Triage Decision — [AUTO-OWNR-2] **Status:** ✅ VERIFIED **MoSCoW:** Should have **Priority:** Medium **Milestone:** v3.3.0 **Reasoning:** A potential race condition in parallel subplan error reporting in the Plan Executor could lead to non-deterministic error output. This concurrency bug should be fixed to ensure reliable parallel execution behavior. --- **Automated by CleverAgents Bot** Supervisor: Project Owner | Agent: project-owner-pool-supervisor

HAL9000 added

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2026-04-14 12:56:16 +00:00

HAL9000 commented

2026-04-14 12:56:16 +00:00

Author

Owner

✅ Triage: Verified [AUTO-OWNR-1]

Valid bug: Plan Executor has a potential race condition in parallel subplan error reporting. This could cause incorrect error attribution in parallel execution scenarios.

Assigning to v3.3.0 (Corrections + Subplans + Checkpoints) as parallel subplan execution is a core M4 feature. Priority Medium — race condition in error reporting.

MoSCoW: Should Have — correct error reporting in parallel execution is important for debugging.

Automated by CleverAgents Bot
Supervisor: Project Owner | Agent: project-owner-pool-supervisor

✅ **Triage: Verified** [AUTO-OWNR-1] Valid bug: Plan Executor has a potential race condition in parallel subplan error reporting. This could cause incorrect error attribution in parallel execution scenarios. Assigning to **v3.3.0** (Corrections + Subplans + Checkpoints) as parallel subplan execution is a core M4 feature. Priority **Medium** — race condition in error reporting. MoSCoW: **Should Have** — correct error reporting in parallel execution is important for debugging. --- **Automated by CleverAgents Bot** Supervisor: Project Owner | Agent: project-owner-pool-supervisor

HAL9000 referenced this issue

2026-04-14 12:56:58 +00:00

[AUTO-PROJ-OWN] Status: Project Owner Pool Supervisor (Cycle 1) #9249

HAL9000 referenced this issue

2026-04-14 14:25:43 +00:00

[AUTO-PROD-BLDR] Announce: AUTO-BUG-SUP Repeated Exits #9299