refine(skills): staff-review round — trim reference rule, close executing-plans spec gap

Staff-review findings (4-reviewer panel):
- Reference paragraph rewritten 170→123 words preserving every
  behavioral condition (paraphrase/summarize coverage, no-skip guard,
  WHAT-WHY/HOW split, No Placeholders boundary, drift counter,
  zero-context rescope); fixes the "(brainstorming did)" syntax.
- **Spec:** header bracket: cut the never-skip sermon duplicated from
  the Overview (same loaded document); the conditional none-branch
  stays.
- executing-plans Step 1 now reads the spec the plan cites — plans are
  no longer self-contained, and the non-subagent execution path was
  never told (the eval only exercised the SDD consumer).
- writing-plans plan-location preference line gets the same
  existing-dir-is-not-a-preference guard as the spec path.
- brainstorming: deduplicate the docs/specs/ prohibition (step 6
  parenthetical stays; After-the-Design bullet was the second
  statement in one file).

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

skills/subagent-driven-development/SKILL.md

@@ -86,10 +86,6 @@ digraph process {
 }
 ```
 
-## Spec Context
-
-If the plan's header cites a spec (`**Spec:** <path>`), read it once during plan extraction. Plans reference requirements rather than restating them — when a task cites a spec section, paste that section's text into the implementer and spec-reviewer prompts along with the task text. Implementer subagents never read the spec file themselves; the spec reviewer may additionally read it at the cited path (its prompt says so).
-
 ## Model Selection
 
 Use the least powerful model that can handle each role to conserve cost and increase speed.

skills/subagent-driven-development/implementer-prompt.md

@@ -12,8 +12,6 @@ Subagent (general-purpose):
 
     [FULL TEXT of task from plan - paste it here, don't make subagent read file]
 
-    [If the task cites spec sections, paste the cited sections' text here too]
-
     ## Context
 
     [Scene-setting: where this fits, dependencies, architectural context]

skills/subagent-driven-development/spec-reviewer-prompt.md

@@ -12,7 +12,7 @@ Subagent (general-purpose):
 
     ## What Was Requested
 
-    [FULL TEXT of task requirements, including the text of any spec sections the task cites]
+    [FULL TEXT of task requirements]
 
     ## What Implementer Claims They Built
 
@@ -28,7 +28,7 @@ Subagent (general-purpose):
     git diff [BASE_SHA]..[HEAD_SHA]
     ```
 
-    Only read files in this diff. Do not crawl the broader codebase. (One exception: if the requirements cite a spec document, you may read that spec at its cited path.)
+    Only read files in this diff. Do not crawl the broader codebase.
 
     ## Read-Only Review
 

skills/writing-plans/SKILL.md

@@ -149,7 +149,7 @@ After saving the plan, offer execution choice:
 
 **If Subagent-Driven chosen:**
 - **REQUIRED SUB-SKILL:** Use superpowers:subagent-driven-development
-- Fresh subagent per task + two-stage review
+- Fresh subagent per task + two-stage review (review fanout scales with the change — see that skill's Proportionality rule)
 
 **If Inline Execution chosen:**
 - **REQUIRED SUB-SKILL:** Use superpowers:executing-plans