/architect, Implementation Architecture from PRD

When to Use

Don't use when: you already have an architecture and want to implement it (use /marshal or /archon); you need a PRD first (use /prd before /architect).

• After /prd produces an approved PRD (greenfield or feature mode)
• When the user has a clear direction + existing codebase (no PRD needed)
• When /do routes a build request
• When the user has a spec and wants a build plan

Inputs

One of:

1. A PRD file path (from /prd), preferred, contains structured requirements
2. A user-provided spec or description + an existing codebase, sufficient
3. Neither, suggest /prd first, but don't hard-gate. If the user has a clear direction ("add auth to my app"), that + the existing code IS the input.

Mode Detection

Greenfield mode: PRD exists with Mode: greenfield, or no existing source files. Produces a complete architecture from scratch.

Feature mode: PRD exists with Mode: feature, OR the user describes a feature and the project has existing source files. The architecture describes changes to existing code, not a standalone system.

In feature mode:

• Read the existing file tree FIRST, understand the current architecture before planning changes
• Read key files (package.json, tsconfig, main entry points, existing patterns)
• The File Tree section shows ONLY new and modified files, not the entire project
• Phases include a Phase 0: "Baseline" that records current typecheck/test state
• Every phase's end conditions include "no new typecheck errors" and "existing tests pass"
• The Risk Register includes "regression in existing functionality" as a default risk

Protocol

Step 1: READ

If PRD exists, read it. Extract:

• Core features (the numbered list)
• Technical decisions (stack choices)
• End conditions (what "done" looks like)
• Out of scope (what NOT to build)
• Integration points (feature mode)