# Decision Gate: Sequential Task Implementation as Default

**Branch**: `colonyos/when_we_implement_a_new_functionality_from_the_tasks_it_should_not_happen_in_par`
**PRD**: `cOS_prds/20260329_213252_prd_when_we_implement_a_new_functionality_from_the_tasks_it_should_not_happen_in_par.md`
**Date**: 2026-03-29

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## Persona Verdicts

| Reviewer | Latest Round | Verdict | Highest Severity |
|----------|-------------|---------|-----------------|
| Andrej Karpathy | Round 4 | ✅ APPROVE | None |
| Linus Torvalds | Round 3 (confirmed fixed in Round 5) | ✅ APPROVE | Feature gap (non-blocking, fixed) |
| Principal Systems Engineer (Google/Stripe) | Round 5 | ✅ APPROVE | INFO |
| Principal Systems Engineer | Round 3 | ✅ APPROVE | LOW |
| Staff Security Engineer | Round 4 | ✅ APPROVE | LOW |

**Tally: 5/5 APPROVE — unanimous**

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## PRD Requirements Coverage

| Requirement | Status |
|-------------|--------|
| FR-1: Default `ParallelImplementConfig.enabled` to `False` | ✅ Done |
| FR-2: Default `DEFAULTS["parallel_implement"]["enabled"]` to `False` | ✅ Done |
| FR-3: Sequential task runner in orchestrator | ✅ Done (`_run_sequential_implement`) |
| FR-4: Uses `TaskDAG.topological_sort()` | ✅ Done |
| FR-5: Git commit between each task | ✅ Done (selective staging, secret filtering) |
| FR-6: Failed → BLOCKED dependents, continue independents | ✅ Done |
| FR-7: Budget = `phase_budget / task_count` | ✅ Done |
| FR-8: Warning when parallel explicitly enabled | ✅ Done |
| FR-9: PhaseResult with per-task breakdown | ✅ Done |
| FR-10: Parallel code untouched, works when opted in | ✅ Done (existing tests updated) |

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## Code Changes Summary

- **`src/colonyos/config.py`**: Default flipped to `False` (2 locations) + warning log when parallel explicitly enabled (+11/-2 lines)
- **`src/colonyos/orchestrator.py`**: New `_build_single_task_implement_prompt()` and `_run_sequential_implement()` functions; refactored `_execute_implement_phase()` routing (+402/-33 lines)
- **`tests/test_sequential_implement.py`**: 922-line new test file with 32 tests covering DAG ordering, failure/blocking, prompt construction, budget allocation, and integration
- **`tests/test_orchestrator.py`**, **`tests/test_parallel_config.py`**, **`tests/test_parallel_orchestrator.py`**: Minor updates to set `parallel_implement.enabled = True` where parallel mode is being tested

---

```
VERDICT: GO
```

### Rationale
All 5 personas unanimously approve. Zero CRITICAL or HIGH findings remain — all issues raised in earlier rounds were addressed through the fix loop (memory injection, context draining, UI callbacks). The implementation cleanly satisfies all 10 functional requirements from the PRD, with a thorough 922-line test suite covering happy paths, failure cascading, transitive blocking, prompt construction, and budget allocation. Security hardening (selective staging, secret filtering, subprocess timeouts, commit message sanitization) is solid.

### Unresolved Issues
None blocking. Minor non-blocking items noted by reviewers:
- Secret filter could be extended to cover `.npmrc`, `.pypirc`, `*.keystore` (pre-existing gap, not introduced by this PR)
- Theoretical `ARG_MAX` limit on `git add --` with thousands of files (practically unlikely per-task)
- Budget savings from fast tasks not redistributed (by-design per PRD)

### Recommendation
Merge as-is. The implementation is clean, well-tested, and addresses the core user pain point (merge conflicts from parallel execution). The sequential-by-default approach with parallel as opt-in is the correct architecture for an autonomous system with dependent task chains.
