Decompose

Decompose — Project Scope Analysis

Analyze project scope and determine whether to treat it as a single feature or split into multiple sub-features before entering the spec chain.

Core Principles

1. Lightweight: 3-5 rounds of questions, not a deep investigation
2. Boundary-focused: Only care about scope boundaries and dependencies
3. No demand validation: That is /idea's responsibility
4. No deep research: That is /prd's responsibility
5. Single is valid: Not every project needs splitting — a single-feature verdict is a good outcome

Workflow

Step 1: Read Context

Scan the project to understand what exists:

@../shared/project-context.md

Execute PC.1 (Project Discovery) and PC.3 (Project Profile):

1. Project structure, README, existing docs (PC.1)
2. Project profile — Web API, CLI, Frontend, etc. (PC.3)
3. Check if ideas/{feature-name}/draft.md exists — if found, read it for context on scope

The project profile informs the decomposition: a monorepo with multiple apps has different split criteria than a single-purpose API. Summarize what you learned in 2-3 sentences. Do not present this to the user — it is internal context for the interview.

Step 2: Scope Interview

Use AskUserQuestion to understand project boundaries. Ask 3-5 rounds of questions, adapting based on answers.

Round 1 — The Shape:

• What are the main functional areas or modules of this project? (e.g., "auth, payments, notifications" or "it's a single API endpoint")
• How big is this project in your mind — a single focused feature, or multiple related features?

Round 2 — Boundaries:

• Which parts could be developed and tested independently?
• Which parts depend on each other? (e.g., "payments needs auth to exist first")
• Are there shared foundations that multiple parts need? (data models, infrastructure, auth)

Round 3+ — Clarification (if needed):

• Follow up on anything unclear from rounds 1-2
• Stop when you can confidently propose a split structure

Do NOT force answers. If the user says "I'm not sure", use your judgment based on what you know.

Step 3: Split Decision & Rationale

Based on the interview, determine: single or multi-split.

Split heuristics:

Good split characteristics:

• Cohesive purpose — a clear goal or outcome
• Bounded complexity — 1-3 major components
• Clear interfaces — well-defined inputs and outputs
• Each split is substantial enough for its own Tech Design + Feature Specs

Rationale requirement: After reaching a verdict, you MUST produce a formal Split Rationale block (see Step 4a / 4b). Do not present the verdict without justification. The rationale must name which heuristics fired with project-specific evidence, and explicitly state why the alternative verdict was rejected.

Step 4a: Single Feature Verdict

If the project is a single feature:

1. Produce the Split Rationale block (required before informing the user):

Split Rationale:
  Verdict: Single feature

  Signals that fired (Single):
    ✓ [Signal text from heuristics table] — [one sentence of project-specific evidence]
    ✓ [Signal text] — [evidence]

  Signals evaluated but not triggered (Multi-split):
    ✗ [Signal text] — [why it does not apply to this project]
    ✗ [Signal text] — [why it does not apply]

  Why not Multi-split: [1-2 sentences explaining why splitting would be premature,
  over-engineered, or harmful for this specific project — reference scope, coupling,
  team size, or other concrete factors from the interview.]

2. Inform the user: "This project is well-scoped as a single feature. Proceeding directly to the spec chain."
3. Return the verdict. Do NOT generate a manifest file.

Step 4b: Multi-Split — Generate Manifest

If the project should be split:

1. Produce the Split Rationale block (required before presenting the breakdown):

Split Rationale:
  Verdict: Multi-split ({N} sub-features)

  Signals that fired (Multi-split):
    ✓ [Signal text from heuristics table] — [one sentence of project-specific evidence]
    ✓ [Signal text] — [evidence]

  Signals evaluated but not triggered (Single):
    ✗ [Signal text] — [why it does not apply to this project]
    ✗ [Signal text] — [why it does not apply]

  Why not Single: [1-2 sentences explaining what makes this project structurally
  too broad or heterogeneous to treat as one feature — e.g., "The auth subsystem
  and payment pipeline share no code paths and require independent deployment cycles."]

  Boundary rationale:
    {sub-feature-1} | {sub-feature-2}: [Why this is a clean cut point — what the
    interface between them is and why each side is independently specifiable]
    [Add one line per boundary if N > 2]

2. Present the proposed split structure together with the rationale to the user for confirmation
3. Use AskUserQuestion: "Here's my proposed breakdown and the reasoning behind it. Does this look right, or would you change anything?"
4. If the user wants changes, adjust rationale accordingly and re-confirm
5. Once confirmed, write the manifest to docs/project-{name}.md

Manifest format:

The file MUST start with a FEATURE_MANIFEST comment block, followed by human-readable content:

<!-- FEATURE_MANIFEST
{sub-feature-1}
{sub-feature-2}
{sub-feature-3}
END_MANIFEST -->

# Project: {name}

## Sub-Features

### 1. {sub-feature-1}
- **Description**: {what this sub-feature covers}
- **Dependencies**: {none, or list of sub-feature names it depends on}
- **Scope**: {brief scope summary}

### 2. {sub-feature-2}
- **Description**: ...
- **Dependencies**: ...
- **Scope**: ...

## Execution Order

{Ordered list with dependency and parallelism notes}

## Cross-Cutting Concerns

{Shared data models, conventions, infrastructure, or other things that span multiple sub-features}

FEATURE_MANIFEST rules:

• CRITICAL: Must be the VERY FIRST thing in the file — no YAML front-matter, no headings, no blank lines before the <!-- FEATURE_MANIFEST comment. The spec-forge chain parser reads from the top and will fail to recognize the manifest if anything precedes it.
• One sub-feature per line, kebab-case (e.g., user-auth, payment-processing)
• Names become directory names under docs/ — each sub-feature gets docs/{name}/tech-design.md
• This block is machine-parseable; the rest of the file is for humans

Step 5: Summary

Display the result:

If single:

Scope analysis complete: {name}
  Verdict: Single feature
  Next: Running spec chain (Tech Design + Feature Specs)

If multi-split:

Scope analysis complete: {name}
  Verdict: {N} sub-features
  Manifest: docs/project-{name}.md

  Sub-features:
    1. {sub-feature-1} — {one-line description}
    2. {sub-feature-2} — {one-line description}
    ...

  Next: Run the full chain for all sub-features:
    /spec-forge {name}