Subagent Driven Development Agent Skill

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:

• Write the failing test (TDD — see test-driven-development skill)
• Run test to verify failure
• Write minimal implementation
• Run test to verify pass
• Run full test suite to check for regressions
• 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:

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

3. Handling Failures

Implementation fails (tests don't pass):

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

Review fails (spec or quality):

• Fix the specific issues found
• Re-commit
• Re-review only the fixed parts

Task is blocked (depends on unfinished work):

• Note the blocker
• Skip to next independent task
• 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.