PM planning — decompose ARCH into tasks

The pm agent's job is to take the architect's ARCH document and produce 2 things:

1. A PLAN-<feature>.md for humans
2. A sequence of bd create tasks for senior-dev to claim

The plan is good if a fresh senior-dev (no prior context) can pick up the bd tasks and ship without coming back for clarification.

The decomposition rules

Rule 1. Tasks ≤ 4 hours

Anything bigger gets split. If the task is "build the auth system", split into:

• Schema migration for user table
• Signup endpoint with hashing
• Login endpoint with JWT issuance
• Logout / token revocation
• Tests

Each ≤ 4h. If you can't split, the task is unclear — go back to ARCH and clarify.

Rule 2. Single output artefact per task

Each task produces ONE of:

• A code file (new or modified)
• A database migration
• A test file
• A documentation update
• A config change

If a task produces multiple unrelated artefacts, split it.

Rule 3. Explicit dependencies via --blocks

When task B requires task A's output:

bd create "Task A: schema migration" -p P1
# returns id: my-proj-001-abc

bd create "Task B: signup endpoint" -p P1 \
  --blocks-on my-proj-001-abc \
  --label senior-dev

The pipeline orchestrator reads bd ready --assignee senior-dev to know what's claimable. Tasks blocked on incomplete predecessors don't appear.

Rule 4. Acceptance criteria — what does "done" mean?

Every task description ends with a bulleted "Done when:" section.

## Done when:
- [ ] POST /signup returns 201 with user_id on success
- [ ] Bad email returns 400 with "invalid_email"
- [ ] Duplicate email returns 409 with "email_taken"
- [ ] Password is hashed with argon2 (no plaintext in DB)
- [ ] Unit test in `tests/auth/signup.test.ts` covers all 4 cases
- [ ] `npm test` passes

Senior-dev knows EXACTLY what to ship and when to stop.

Rule 5. Owners and parallelism

If 3 tasks can run in parallel, mark each with the agent it goes to. Don't bundle them.

bd create "..." --label senior-dev
bd create "..." --label senior-dev   # parallel
bd create "..." --label devops       # parallel, different agent

The PLAN-*.md template

# PLAN — <feature>

Date: <ISO>
Architect ARCH: docs/architecture/ARCH-<feature>.md
Owner: pm

## Summary

2-3 sentences. What problem, what solution. Reference ARCH for detail.

## Cost estimate

(Follow skill: cost-model)

## Tasks

1. **<title>** [P1, ≤2h, senior-dev]
   - Goal: <one-sentence>
   - Done when: <bulleted criteria>
   - bd id: <ID after create>

2. **<title>** [P1, ≤4h, senior-dev]
   - Blocked on: 1
   - Goal: ...
   - Done when: ...

3. **<title>** [P2, ≤1h, qa-engineer]
   - Blocked on: 1, 2

## Pre-mortem

(Follow skill: pre-mortem)

## Gates

(Follow GATES_BY_ARCHETYPE for this archetype + project_size)
- [ ] gate:plan — after pm finishes, before senior-dev starts
- [ ] gate:qa — after qa-engineer, before ship
- [ ] gate:ship — after security-officer, before devops

When pm should push back instead of plan

The pm agent is allowed — and EXPECTED — to refuse a plan if the ARCH is incomplete. Specifically:

❌ ARCH is missing acceptance criteria for the feature itself. Push back: "ARCH says 'build webhook handler' but doesn't specify what counts as success. Re-architect with explicit success criteria."

❌ ARCH doesn't specify the failure mode. Push back: "ARCH says 'handle errors gracefully' but doesn't say what 'graceful' means. Define: log + ack? log + retry? log + alert?"

❌ ARCH conflicts with existing ADRs. Push back: "ARCH proposes Postgres but ADR-005 mandated DynamoDB. Resolve before plan."

Push-back goes to the architect with bd update + label re-arch. The plan is BLOCKED until ARCH is refined.

Anti-patterns

❌ Tasks named after components, not goals. "Build UserService" is ambiguous. "Add POST /signup endpoint that hashes password with argon2" is clear.

❌ No dependencies declared. Two tasks editing the same file with no --blocks-on will conflict. Always declare.

❌ Estimating without doing one task. If you genuinely don't know how long task 1 takes, ask senior-dev to do task 1 first and report back. THEN estimate 2–N.

❌ Tasks > 8 hours. Split. No exceptions.