fix(skills): plans reference the spec instead of restating it (SUP-333 #1)

writing-plans told agents to "document everything they need to know"
assuming zero context — every agent in the 2026-06-09 six-agent quorum
sweep obeyed and restated the entire spec inline in the plan
(cost-spec-plan-duplication failed 5/5 completed agents; pi's plan was
683 lines of duplicated spec).

- writing-plans: state the division of labor — spec owns WHAT/WHY,
  plan owns HOW; cite the spec by path/section, never restate it.
  "Zero context" means mechanically executable steps, not duplication.
  Add a **Spec:** line to the plan header template.
- brainstorming: close the path loophole the re-run exposed — claude
  shortened docs/superpowers/specs/ to docs/specs/ in 2/2 runs; both
  path mentions now explicitly forbid the shortening.

TDD evidence (quorum):
- RED: batch-20260609T023452Z-68aa et al — 5/5 agents fail
- GREEN: cost-spec-plan-duplication-claude-20260609T234142Z-9625 pass
  (plan: "this plan does not restate them" + spec cited by path;
  both docs in docs/superpowers/)
- Canary: triggering-writing-plans-claude pass (skill still fires)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

skills/brainstorming/SKILL.md

@@ -26,7 +26,7 @@ You MUST create a task for each of these items and complete them in order:
 3. **Ask clarifying questions** — one at a time, understand purpose/constraints/success criteria
 4. **Propose 2-3 approaches** — with trade-offs and your recommendation
 5. **Present design** — in sections scaled to their complexity, get user approval after each section
-6. **Write design doc** — save to `docs/superpowers/specs/YYYY-MM-DD-<topic>-design.md` and commit
+6. **Write design doc** — save to `docs/superpowers/specs/YYYY-MM-DD-<topic>-design.md` and commit (exactly this path — not `docs/specs/`)
 7. **Spec self-review** — quick inline check for placeholders, contradictions, ambiguity, scope (see below)
 8. **User reviews written spec** — ask user to review the spec file before proceeding
 9. **Transition to implementation** — invoke writing-plans skill to create implementation plan
@@ -109,6 +109,7 @@ digraph brainstorming {
 **Documentation:**
 
 - Write the validated design (spec) to `docs/superpowers/specs/YYYY-MM-DD-<topic>-design.md`
+  - The `docs/superpowers/` prefix is the convention; do not shorten it to `docs/specs/`
   - (User preferences for spec location override this default)
 - Use elements-of-style:writing-clearly-and-concisely skill if available
 - Commit the design document to git

skills/writing-plans/SKILL.md

@@ -7,10 +7,12 @@ description: Use when you have a spec or requirements for a multi-step task, bef
 
 ## Overview
 
-Write comprehensive implementation plans assuming the engineer has zero context for our codebase and questionable taste. Document everything they need to know: which files to touch for each task, code, testing, docs they might need to check, how to test it. Give them the whole plan as bite-sized tasks. DRY. YAGNI. TDD. Frequent commits.
+Write comprehensive implementation plans assuming the engineer has zero context for our codebase and questionable taste. Document everything they need to execute: which files to touch for each task, code, testing, docs they might need to check, how to test it. Give them the whole plan as bite-sized tasks. DRY. YAGNI. TDD. Frequent commits.
 
 Assume they are a skilled developer, but know almost nothing about our toolset or problem domain. Assume they don't know good test design very well.
 
+**Plans reference the spec; they never restate it.** The spec owns the WHAT and WHY — requirements, acceptance criteria, design decisions. The plan owns the HOW — tasks, files, code, commands. Cite the spec by path in the header and by section where a task needs context. Re-deriving spec content inline doubles the documents and lets them drift apart. "Zero context" means the engineer can execute each step mechanically; it does not mean the plan repeats what the spec already says — they can read the spec at the cited path.
+
 **Announce at start:** "I'm using the writing-plans skill to create the implementation plan."
 
 **Context:** If working in an isolated worktree, it should have been created via the `superpowers:using-git-worktrees` skill at execution time.
@@ -53,6 +55,8 @@ This structure informs the task decomposition. Each task should produce self-con
 
 **Goal:** [One sentence describing what this builds]
 
+**Spec:** [Path to the spec doc, e.g. `docs/superpowers/specs/YYYY-MM-DD-<topic>-design.md` — requirements and design decisions live there; do not restate them here]
+
 **Architecture:** [2-3 sentences about approach]
 
 **Tech Stack:** [Key technologies/libraries]