feat: learnings + confidence resolvers — cross-skill memory infrastructure

Three new resolvers for the self-learning system:
- LEARNINGS_SEARCH: tells skills to load prior learnings before analysis
- LEARNINGS_LOG: tells skills to capture discoveries after completing work
- CONFIDENCE_CALIBRATION: adds 1-10 confidence scoring to all review findings

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

scripts/resolvers/learnings.ts

@@ -0,0 +1,96 @@
+/**
+ * Learnings resolver — cross-skill institutional memory
+ *
+ * Learnings are stored per-project at ~/.gstack/projects/{slug}/learnings.jsonl.
+ * Each entry is a JSONL line with: ts, skill, type, key, insight, confidence,
+ * source, branch, commit, files[].
+ *
+ * Storage is append-only. Duplicates (same key+type) are resolved at read time
+ * by gstack-learnings-search ("latest winner" per key+type).
+ *
+ * Cross-project discovery is opt-in. The resolver asks the user once via
+ * AskUserQuestion and persists the preference via gstack-config.
+ */
+import type { TemplateContext } from './types';
+
+export function generateLearningsSearch(ctx: TemplateContext): string {
+  if (ctx.host === 'codex') {
+    // Codex: simpler version, no cross-project, uses $GSTACK_BIN
+    return `## Prior Learnings
+
+Search for relevant learnings from previous sessions on this project:
+
+\`\`\`bash
+$GSTACK_BIN/gstack-learnings-search --limit 10 2>/dev/null || true
+\`\`\`
+
+If learnings are found, incorporate them into your analysis. When a review finding
+matches a past learning, note it: "Prior learning applied: [key] (confidence N, from [date])"`;
+  }
+
+  return `## Prior Learnings
+
+Search for relevant learnings from previous sessions:
+
+\`\`\`bash
+_CROSS_PROJ=$(${ctx.paths.binDir}/gstack-config get cross_project_learnings 2>/dev/null || echo "unset")
+echo "CROSS_PROJECT: $_CROSS_PROJ"
+if [ "$_CROSS_PROJ" = "true" ]; then
+  ${ctx.paths.binDir}/gstack-learnings-search --limit 10 --cross-project 2>/dev/null || true
+else
+  ${ctx.paths.binDir}/gstack-learnings-search --limit 10 2>/dev/null || true
+fi
+\`\`\`
+
+If \`CROSS_PROJECT\` is \`unset\` (first time): Use AskUserQuestion:
+
+> gstack can search learnings from your other projects on this machine to find
+> patterns that might apply here. This stays local (no data leaves your machine).
+> Recommended for solo developers. Skip if you work on multiple client codebases
+> where cross-contamination would be a concern.
+
+Options:
+- A) Enable cross-project learnings (recommended)
+- B) Keep learnings project-scoped only
+
+If A: run \`${ctx.paths.binDir}/gstack-config set cross_project_learnings true\`
+If B: run \`${ctx.paths.binDir}/gstack-config set cross_project_learnings false\`
+
+Then re-run the search with the appropriate flag.
+
+If learnings are found, incorporate them into your analysis. When a review finding
+matches a past learning, display:
+
+**"Prior learning applied: [key] (confidence N/10, from [date])"**
+
+This makes the compounding visible. The user should see that gstack is getting
+smarter on their codebase over time.`;
+}
+
+export function generateLearningsLog(ctx: TemplateContext): string {
+  const binDir = ctx.host === 'codex' ? '$GSTACK_BIN' : ctx.paths.binDir;
+
+  return `## Capture Learnings
+
+If you discovered a non-obvious pattern, pitfall, or architectural insight during
+this session, log it for future sessions:
+
+\`\`\`bash
+${binDir}/gstack-learnings-log '{"skill":"${ctx.skillName}","type":"TYPE","key":"SHORT_KEY","insight":"DESCRIPTION","confidence":N,"source":"SOURCE","files":["path/to/relevant/file"]}'
+\`\`\`
+
+**Types:** \`pattern\` (reusable approach), \`pitfall\` (what NOT to do), \`preference\`
+(user stated), \`architecture\` (structural decision), \`tool\` (library/framework insight).
+
+**Sources:** \`observed\` (you found this in the code), \`user-stated\` (user told you),
+\`inferred\` (AI deduction), \`cross-model\` (both Claude and Codex agree).
+
+**Confidence:** 1-10. Be honest. An observed pattern you verified in the code is 8-9.
+An inference you're not sure about is 4-5. A user preference they explicitly stated is 10.
+
+**files:** Include the specific file paths this learning references. This enables
+staleness detection: if those files are later deleted, the learning can be flagged.
+
+**Only log genuine discoveries.** Don't log obvious things. Don't log things the user
+already knows. A good test: would this insight save time in a future session? If yes, log it.`;
+}