Plan Phase

Build a structured execution plan for Phase $ARGUMENTS and write it to phase$ARGUMENTS_plan.md in the project root.

Step 1: Read the Source Documents

Read all four source documents before writing anything. Extract specific things from each:

• implementation_plan.md — Find Phase $ARGUMENTS. Copy its task list verbatim — you're planning exactly what it specifies, not a reinterpretation.
• requirements.md — Find the requirement IDs this phase satisfies. You'll reference these in acceptance criteria.
• design.md — Pull relevant UI layouts, data models, and component patterns for this phase.
• technology_decisions.md — Extract constraints that affect implementation (auth patterns, DB layer, API conventions).

Also scan for existing phase*_plan.md files. Skim any prior phase plans to understand what's already built — so you don't re-plan completed work or misstate dependencies.

Step 2: Assess Phase Size

Count the tasks in Phase $ARGUMENTS from implementation_plan.md.

3–8 tasks spanning a single system boundary → plan the full phase as-is.

>8 tasks OR spans multiple system boundaries (e.g., DB schema + UI + email + auth) → split into labeled sub-phases:

• Phase $ARGUMENTSa: [first boundary]
• Phase $ARGUMENTSb: [second boundary]
• Phase $ARGUMENTSc: [third if needed]

If you split, ask: "Phase $ARGUMENTS is large. I've divided it into sub-phases Xa, Xb, Xc — [one line each]. Which would you like to plan first?"

If you're thinking...	Do this instead
"This phase is straightforward, I can plan it loosely"	Loose plans produce loose implementations. Every task needs files-to-touch and acceptance criteria.
"I'll figure out the details during execution"	Execution is not the time for design decisions. That's how scope creep starts.
"8 tasks is fine for one phase"	The rule is 3-8. If you're at 8, check whether any task crosses a system boundary. If so, split.
"The requirements doc covers this, I don't need to repeat it in the plan"	The plan is the implementer's contract. It must be self-contained. REQ-IDs link back, but the plan states the work.

Step 3: Write the Plan

Write phase$ARGUMENTS_plan.md using this exact template. Keep all fields tight — this document is consumed by /execute-phase, not read by humans.

# Phase $ARGUMENTS: [Title from implementation_plan.md]

## Summary

| # | Task | Requirements |
|---|------|-------------|
| 1 | [Task name] | REQ-XX-1, REQ-XX-2 |
| 2 | [Task name] | REQ-XX-3 |

## Dependencies

- [ ] [Specific thing from a prior phase to verify before starting — e.g., "migration 0012 applied"]
- [ ] [Env var, service, or external dep that must exist]

*None — if no dependencies.*

---

## Tasks

### Task 1: [Name]

**What:** [One sentence — what to build or change]

**Files:**
- Create: `path/to/file.ts`
- Modify: `path/to/other.ts` — [what to add/change]

**AC:**
- [ ] [Specific, testable criterion — reference REQ-XX-1]
- [ ] [Another criterion]
- [ ] [For tasks with unusual security surface: relevant security criterion, e.g., "uploaded files validated for type and size before storage"]

---

### Task 2: [Name]

**What:** [One sentence]

**Files:**
- Modify: `path/to/file.ts` — [what to add/change]

**AC:**
- [ ] [Criterion]

---

[Repeat for all tasks]

---

## Tests

| Test | File | Verifies |
|------|------|---------|
| [test name] | `src/__tests__/foo.test.ts` | [behavior] |

Step 4: Confirm

After writing the file, output:

Phase $ARGUMENTS plan written — [N] tasks.

1. [Task 1 name]
2. [Task 2 name]
...

Requirements satisfied: [REQ list]
Dependencies: [list or "none"]

Run `/execute-phase $ARGUMENTS` to build.

When to Use

• User says "plan phase X", "break down phase X", "scope phase X", "what goes into phase X", "what needs to happen in phase X"
• Starting a new implementation phase from implementation_plan.md

When NOT to Use

• Initial project setup → /kickoff
• Technology decisions → /tech-stack
• Ad-hoc feature with no implementation_plan.md → just ask Claude directly
• Ready to build → /execute-phase