Subagent Driven Development

Subagent-Driven Development

Overview

Execute implementation plans task-by-task with systematic two-stage review between tasks.

Core principle: Fresh focus per task + two-stage review (spec then quality) = high quality, fast iteration.

Poirot note: The original skill dispatches a fresh subagent per task via delegate_task. Poirot has no subagents, so this version executes tasks sequentially in the same context with a deliberate context-reset between tasks. The two-stage review methodology is preserved.

When to Use

• You have an implementation plan (from the plan skill or user requirements)
• Tasks are mostly independent
• Quality and spec compliance are important
• You want automated review between tasks

The Process

1. Read and Parse Plan

Read the plan file. Extract ALL tasks with full text and context upfront:

read_file(".poirot/plans/feature-plan.md")

Create a todo list with all tasks. Read the plan ONCE — don't re-read per task.

2. Per-Task Workflow

For EACH task in the plan:

Step 1: Context Reset

Before starting each task, deliberately reset your focus:

• Re-read only the current task's description
• Forget previous tasks' implementation details (they're committed)
• Treat each task as if a fresh agent is picking it up

Step 2: Implement

Follow the task's steps exactly:

1. Write the failing test (TDD — see test-driven-development skill)
2. Run test to verify failure
3. Write minimal implementation
4. Run test to verify pass
5. Run full test suite to check for regressions
6. Commit

bash("pytest tests/test_feature.py::test_name -v")
# ... implement ...
bash("pytest tests/ -q")
bash("git add -A && git commit -m 'feat: task N description'")

Step 3: Stage 1 Review — Spec Compliance

After implementation, review against the plan:

• Does the implementation match the task's stated objective?
• Are all files listed in the task created/modified?
• Are all tests listed in the task written?
• Does the implementation do what the task says, not more, not less?

If spec compliance fails: Fix before proceeding to Stage 2.

Step 4: Stage 2 Review — Code Quality

Review the committed diff for quality:

• No hardcoded secrets, credentials
• Input validation on user-provided data
• Error handling for I/O/network/DB
• No debug print/console.log left behind
• No commented-out code
• Tests cover happy path + edge cases
• Code follows project conventions

Use the requesting-code-review skill's checklist for thoroughness.

If quality review fails: Fix, re-commit, re-review.

Step 5: Proceed to Next Task

Only after both reviews pass:

1. Mark current task complete in the todo list
2. Move to next task
3. Repeat from Step 1 (Context Reset)

3. Handling Failures

Implementation fails (tests don't pass):

1. Use systematic-debugging skill to find root cause
2. Fix the root cause
3. Re-run tests
4. If 3+ fixes fail → question the approach, discuss with user

Review fails (spec or quality):

1. Fix the specific issues found
2. Re-commit
3. Re-review only the fixed parts

Task is blocked (depends on unfinished work):

1. Note the blocker
2. Skip to next independent task
3. Return to blocked task when dependency is resolved

Two-Stage Review Detail

Stage 1: Spec Compliance

Re-read the task from the plan. Compare against what you actually built:

Task says: "Create User model with email and password_hash fields"
Check:
- [ ] User model exists
- [ ] Has email field
- [ ] Has password_hash field
- [ ] No extra fields not in the task
- [ ] Test exists for the model

Common spec violations:

• Implementing more than the task asks ("while I'm here" scope creep)
• Missing a file the task lists
• Different API shape than the task specifies
• No test for the feature

Stage 2: Code Quality

Review the git diff for the current task:

bash("git diff HEAD~1 HEAD")

Check for security, correctness, and conventions. Use the requesting-code-review skill's security scan + self-review checklist.

Pitfalls

• Context accumulation: without subagents, context grows across tasks. If you feel confused about which task you're on, re-read the plan + current task.
• Scope creep: "while I'm here" edits to previous tasks' code. Don't. Each task is atomic.
• Skipping review: the two-stage review IS the value of this skill. Without it, you're just implementing sequentially.
• Re-reviewing everything: after a fix, only re-review the fixed parts, not the entire task.
• Forgetting to commit: commit after each task. Don't accumulate uncommitted changes across tasks — if a later task breaks, you can't cleanly revert.