test: /learn E2E — seed 3 learnings, verify agent surfaces them

Seeds N+1 query pattern, stale cache pitfall, and rubocop preference
into learnings.jsonl, then runs /learn and checks that at least 2/3
appear in the agent's output. Gate tier, ~$0.25/run.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

test/helpers/touchfiles.ts

@@ -95,6 +95,9 @@ export const E2E_TOUCHFILES: Record<string, string[]> = {
   'cso-diff-mode':    ['cso/**'],
   'cso-infra-scope':  ['cso/**'],
 
+  // Learnings
+  'learnings-show': ['learn/**', 'bin/gstack-learnings-search', 'bin/gstack-learnings-log', 'scripts/resolvers/learnings.ts'],
+
   // Document-release
   'document-release': ['document-release/**'],
 
@@ -238,6 +241,9 @@ export const E2E_TIERS: Record<string, 'gate' | 'periodic'> = {
   'cso-diff-mode': 'gate',
   'cso-infra-scope': 'periodic',
 
+  // Learnings — gate (functional guardrail: seeded learnings must appear)
+  'learnings-show': 'gate',
+
   // Document-release — gate (CHANGELOG guardrail)
   'document-release': 'gate',