fix(skills): brainstorming gate exempts requests with nothing to design (SUP-333 #3)

The HARD-GATE ("EVERY project regardless of perceived simplicity") plus
the anti-pattern list naming "a config change" made design+approval
mandatory even for fully-specified trivial asks — all 6 agents in the
2026-06-09 quorum sweep ran a multi-option design flow for "a basic
checkbox, nothing fancy" (cost-checkbox-over-trigger failed 6/6).

Two layers, because routing happens before skill content is read
(GREEN attempt 1 proved it: the agent invoked the skill on the
description's mandate and only then saw the in-skill exception, and
the invocation itself is the cost event):

- description: carve-out visible at skill-selection time — zero open
  design decisions, fully specified trivial change → implement
  directly without invoking.
- HARD-GATE: matching exception with objective re-gating tripwires
  (new file/dependency, schema/API/data question, >1 plausible
  interpretation, user frames it as a feature/project), and the
  anti-pattern section now distinguishes "seems simple" (a
  rationalization when decisions exist) from "contains every decision"
  (the exception). "A config change" moves from the all-of-them list
  to the exception's example.

The repo's acceptance test ("Let's make a react todo list" must
auto-trigger brainstorming) is unaffected: a react todo list leaves
many decisions open and todo lists remain in the anti-pattern list.

TDD evidence (quorum):
- RED: cost-checkbox-over-trigger fails 6/6 agents (batch 2026-06-09);
  GREEN attempt 1 with in-skill exception only: still fail (invoked
  via description, then asked a clarifying question)
- GREEN: cost-checkbox-over-trigger-claude-20260610T004320Z-a30e pass —
  no brainstorming invocation, agent cited the exception verbatim,
  checkbox landed in 31s
- Canary: cost-spec-plan-duplication-claude-20260610T004506Z-22ea pass —
  a real feature still triggers the full brainstorm→spec→plan flow
  (and the stacked writing-plans reference discipline holds)

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

skills/brainstorming/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: brainstorming
-description: "You MUST use this before any creative work - creating features, building components, adding functionality, or modifying behavior. Explores user intent, requirements and design before implementation."
+description: "You MUST use this before any creative work - creating features, building components, adding functionality, or modifying behavior. Explores user intent, requirements and design before implementation. The one exception: a request that leaves zero design decisions open (a fully specified trivial change, e.g. 'add a basic checkbox, nothing fancy') needs no design - implement it directly without invoking this skill."
 ---
 
 # Brainstorming Ideas Into Designs
@@ -11,11 +11,13 @@ Start by understanding the current project context, then ask questions one at a
 
 <HARD-GATE>
 Do NOT invoke any implementation skill, write any code, scaffold any project, or take any implementation action until you have presented a design and the user has approved it. This applies to EVERY project regardless of perceived simplicity.
+
+Exception — nothing to design: if the request leaves no design decisions open — the user has fully specified the outcome and there is exactly one reasonable way to do it (e.g. "add a basic checkbox, nothing fancy", a literal config value change, a copy fix) — implement it directly. Brainstorming exists to surface decisions; when there are none, the user's request IS the design. Any of these put the gate back on: a new file or dependency, a schema/API/data question, more than one plausible interpretation, or the user framing it as a feature or project to think through.
 </HARD-GATE>
 
 ## Anti-Pattern: "This Is Too Simple To Need A Design"
 
-Every project goes through this process. A todo list, a single-function utility, a config change — all of them. "Simple" projects are where unexamined assumptions cause the most wasted work. The design can be short (a few sentences for truly simple projects), but you MUST present it and get approval.
+Projects go through this process. A todo list, a single-function utility, a data migration — "simple" projects are where unexamined assumptions cause the most wasted work. The design can be short (a few sentences for truly simple projects), but if anything remains to decide, you MUST present it and get approval. Do not confuse this with the nothing-to-design exception above: "this seems simple, I'll skip the design" is a rationalization whenever decisions exist — the exception applies only when the user's request already contains every decision.
 
 ## Checklist
 

skills/subagent-driven-development/SKILL.md

@@ -11,6 +11,8 @@ Execute plan by dispatching fresh subagent per task, with two-stage review after
 
 **Core principle:** Fresh subagent per task + two-stage review (spec then quality) = high quality, fast iteration
 
+**Proportionality:** Review fanout scales with the change. When the entire plan is one trivial, fully-specified mechanical change — a one-line edit, a log statement, a constant bump — implement it directly (or with a single implementer subagent), verify it, and commit. Skip the review subagents and the final reviewer: a diff with no room for interpretation has nothing for a spec or quality review to catch, and three dispatches for one line cost more than the change itself. When in doubt whether a change is trivial, it is not — run the full pipeline. Within a multi-task plan, run the full pipeline for every task regardless of size; this exception applies only when the whole plan is one trivial change.
+
 **Continuous execution:** Do not pause to check in with your human partner between tasks. Execute all tasks from the plan without stopping. The only reasons to stop are: BLOCKED status you cannot resolve, ambiguity that genuinely prevents progress, or all tasks complete. "Should I continue?" prompts and progress summaries waste their time — they asked you to execute the plan, so execute it.
 
 ## When to Use
@@ -61,11 +63,16 @@ digraph process {
     }
 
     "Read plan, extract all tasks with full text, note context, create todos" [shape=box];
+    "Entire plan = one trivial mechanical change?" [shape=diamond];
+    "Implement directly, verify, commit (no review fanout)" [shape=box];
     "More tasks remain?" [shape=diamond];
     "Dispatch final code reviewer subagent for entire implementation" [shape=box];
     "Use superpowers:finishing-a-development-branch" [shape=box style=filled fillcolor=lightgreen];
 
-    "Read plan, extract all tasks with full text, note context, create todos" -> "Dispatch implementer subagent (./implementer-prompt.md)";
+    "Read plan, extract all tasks with full text, note context, create todos" -> "Entire plan = one trivial mechanical change?";
+    "Entire plan = one trivial mechanical change?" -> "Implement directly, verify, commit (no review fanout)" [label="yes — see Proportionality"];
+    "Implement directly, verify, commit (no review fanout)" -> "Use superpowers:finishing-a-development-branch";
+    "Entire plan = one trivial mechanical change?" -> "Dispatch implementer subagent (./implementer-prompt.md)" [label="no"];
     "Dispatch implementer subagent (./implementer-prompt.md)" -> "Implementer subagent asks questions?";
     "Implementer subagent asks questions?" -> "Answer questions, provide context" [label="yes"];
     "Answer questions, provide context" -> "Dispatch implementer subagent (./implementer-prompt.md)";
@@ -237,7 +244,7 @@ Done!
 
 **Never:**
 - Start implementation on main/master branch without explicit user consent
-- Skip reviews (spec compliance OR code quality)
+- Skip reviews (spec compliance OR code quality) on a non-trivial task — the Proportionality exception covers only a plan that is one trivial mechanical change
 - Proceed with unfixed issues
 - Dispatch multiple implementation subagents in parallel (conflicts)
 - Make subagent read plan file (provide full text instead)