feat(cdt): enforce task size ≤3 files and strengthen scope lock

[rube-de]

Part of #104

Context

CDT's architect prompt has no task size constraint — tasks are whatever size the architect decides. Large tasks (touching 5+ files) escape context coherence, causing agents to hallucinate connections between unrelated parts. The scope lock directive at dev-workflow.md:70 exists ("Stay within files specified in each task") but is a soft instruction, not a constraint the architect designs around.

Elite practice: 1-3 files per task, single concern, independently verifiable.

Task

Add a task size rule to the architect's prompt in plan-workflow.md and strengthen the scope lock directive in dev-workflow.md.

Acceptance Criteria

• VERIFY: Architect prompt includes rule: "Each task must touch ≤3 files and represent a single concern that is independently verifiable"
• VERIFY: If a task requires >3 files, architect must split it into sub-tasks or justify the exception in the plan
• VERIFY: Developer prompt scope lock is strengthened to explicitly prohibit modifying files not listed in the task's location field
• VERIFY: Plan template task definition includes a files_limit note or convention

Implementation Guide

Files to Modify

• plugins/cdt/skills/cdt/references/plan-workflow.md — Add task size rule to architect prompt (after line 72, in the numbered instructions)
• plugins/cdt/skills/cdt/references/dev-workflow.md — Strengthen scope lock at line 70

Approach

1. In plan-workflow.md, architect prompt (lines 62-139), add after step 6 ("Design: components, interfaces..."):

   Task sizing rule: Each task MUST touch ≤3 files and represent a single independently-verifiable concern. If a change requires >3 files, split into multiple tasks with explicit dependencies. Exception: documentation-update tasks (Step 8) may touch more files.
   

2. In dev-workflow.md, line 70, strengthen:

   Scope lock: ONLY modify files listed in your task's `location` field. If you discover a needed change outside your task's files, message the lead — do NOT expand scope. Exception: Step 10 documentation updates.
   

3. Optionally add a note in the plan template task definition (plan-workflow.md line 113) reminding the architect: - **location**: [file paths — max 3 files per task]

Patterns to Follow

• The existing task template (plan-workflow.md lines 111-118) has a location field — task size rule reinforces this
• The existing scope instruction (dev-workflow.md:70) is the foundation — we're making it a hard rule

Scope

In Scope

• Adding task size rule to architect prompt
• Strengthening scope lock in developer prompt
• Optional: adding max-files note to plan template

Out of Scope

• Enforcing task size via hooks or scripts
• Changing wave execution logic

Dependencies

• Blocked by: None
• Blocks: None

Definition of Done

• Implementation complete
• bun scripts/validate-plugins.mjs passes
• PR approved and merged
• Epic checklist updated