feat: preamble context recovery + timeline events + predictive suggestions

Layers 1-3 of the Session Intelligence Layer:
- Timeline start/complete events injected into every skill via preamble
- Context recovery (tier 2+): lists recent CEO plans, checkpoints, reviews
- Cross-session injection: LAST_SESSION and LATEST_CHECKPOINT for branch
- Predictive skill suggestion from recent timeline patterns
- Welcome back message synthesis
- Routing rules for /checkpoint and /health

Timeline writes are NOT gated by telemetry (local project intelligence).

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

scripts/resolvers/preamble.ts

@@ -77,6 +77,8 @@ if [ -f "$_LEARN_FILE" ]; then
 else
   echo "LEARNINGS: 0"
 fi
+# Session timeline: record skill start (local-only, never sent anywhere)
+${ctx.paths.binDir}/gstack-timeline-log '{"skill":"${ctx.skillName}","event":"started","branch":"'"$_BRANCH"'","session":"'"$_SESSION_ID"'"}' 2>/dev/null &
 # Check if CLAUDE.md has routing rules
 _HAS_ROUTING="no"
 if [ -f CLAUDE.md ] && grep -q "## Skill routing" CLAUDE.md 2>/dev/null; then
@@ -210,6 +212,8 @@ Key routing rules:
 - Design system, brand → invoke design-consultation
 - Visual audit, design polish → invoke design-review
 - Architecture review → invoke plan-eng-review
+- Save progress, checkpoint, resume → invoke checkpoint
+- Code quality, health check → invoke health
 \`\`\`
 
 Then commit the change: \`git add CLAUDE.md && git commit -m "chore: add gstack skill routing rules to CLAUDE.md"\`
@@ -443,6 +447,8 @@ Run this bash:
 _TEL_END=$(date +%s)
 _TEL_DUR=$(( _TEL_END - _TEL_START ))
 rm -f ~/.gstack/analytics/.pending-"$_SESSION_ID" 2>/dev/null || true
+# Session timeline: record skill completion (local-only, never sent anywhere)
+~/.claude/skills/gstack/bin/gstack-timeline-log '{"skill":"SKILL_NAME","event":"completed","branch":"'$(git branch --show-current 2>/dev/null || echo unknown)'","outcome":"OUTCOME","duration_s":"'"$_TEL_DUR"'","session":"'"$_SESSION_ID"'"}' 2>/dev/null || true
 # Local + remote telemetry (both gated by _TEL setting)
 if [ "$_TEL" != "off" ]; then
   echo '{"skill":"SKILL_NAME","duration_s":"'"$_TEL_DUR"'","outcome":"OUTCOME","browse":"USED_BROWSE","session":"'"$_SESSION_ID"'","ts":"'$(date -u +%Y-%m-%dT%H:%M:%SZ)'"}' >> ~/.gstack/analytics/skill-usage.jsonl 2>/dev/null || true
@@ -570,16 +576,65 @@ Avoid filler, throat-clearing, generic optimism, founder cosplay, and unsupporte
 **Final test:** does this sound like a real cross-functional builder who wants to help someone make something people want, ship it, and make it actually work?`;
 }
 
+function generateContextRecovery(ctx: TemplateContext): string {
+  const binDir = ctx.host === 'codex' ? '$GSTACK_BIN' : ctx.paths.binDir;
+
+  return `## Context Recovery
+
+After compaction or at session start, check for recent project artifacts.
+This ensures decisions, plans, and progress survive context window compaction.
+
+\`\`\`bash
+eval "$(${binDir}/gstack-slug 2>/dev/null)"
+_PROJ="\${GSTACK_HOME:-$HOME/.gstack}/projects/\${SLUG:-unknown}"
+if [ -d "$_PROJ" ]; then
+  echo "--- RECENT ARTIFACTS ---"
+  # Last 3 artifacts across ceo-plans/ and checkpoints/
+  find "$_PROJ/ceo-plans" "$_PROJ/checkpoints" -type f -name "*.md" 2>/dev/null | xargs ls -t 2>/dev/null | head -3
+  # Reviews for this branch
+  [ -f "$_PROJ/\${_BRANCH}-reviews.jsonl" ] && echo "REVIEWS: $(wc -l < "$_PROJ/\${_BRANCH}-reviews.jsonl" | tr -d ' ') entries"
+  # Timeline summary (last 5 events)
+  [ -f "$_PROJ/timeline.jsonl" ] && tail -5 "$_PROJ/timeline.jsonl"
+  # Cross-session injection
+  if [ -f "$_PROJ/timeline.jsonl" ]; then
+    _LAST=$(grep "\\"branch\\":\\"\${_BRANCH}\\"" "$_PROJ/timeline.jsonl" 2>/dev/null | grep '"event":"completed"' | tail -1)
+    [ -n "$_LAST" ] && echo "LAST_SESSION: $_LAST"
+    # Predictive skill suggestion: check last 3 completed skills for patterns
+    _RECENT_SKILLS=$(grep "\\"branch\\":\\"\${_BRANCH}\\"" "$_PROJ/timeline.jsonl" 2>/dev/null | grep '"event":"completed"' | tail -3 | grep -o '"skill":"[^"]*"' | sed 's/"skill":"//;s/"//' | tr '\\n' ',')
+    [ -n "$_RECENT_SKILLS" ] && echo "RECENT_PATTERN: $_RECENT_SKILLS"
+  fi
+  _LATEST_CP=$(find "$_PROJ/checkpoints" -name "*.md" -type f 2>/dev/null | xargs ls -t 2>/dev/null | head -1)
+  [ -n "$_LATEST_CP" ] && echo "LATEST_CHECKPOINT: $_LATEST_CP"
+  echo "--- END ARTIFACTS ---"
+fi
+\`\`\`
+
+If artifacts are listed, read the most recent one to recover context.
+
+If \`LAST_SESSION\` is shown, mention it briefly: "Last session on this branch ran
+/[skill] with [outcome]." If \`LATEST_CHECKPOINT\` exists, read it for full context
+on where work left off.
+
+If \`RECENT_PATTERN\` is shown, look at the skill sequence. If a pattern repeats
+(e.g., review,ship,review), suggest: "Based on your recent pattern, you probably
+want /[next skill]."
+
+**Welcome back message:** If any of LAST_SESSION, LATEST_CHECKPOINT, or RECENT ARTIFACTS
+are shown, synthesize a one-paragraph welcome briefing before proceeding:
+"Welcome back to {branch}. Last session: /{skill} ({outcome}). [Checkpoint summary if
+available]. [Health score if available]." Keep it to 2-3 sentences.`;
+}
+
 // Preamble Composition (tier → sections)
 // ─────────────────────────────────────────────
 // T1: core + upgrade + lake + telemetry + voice(trimmed) + contributor + completion
-// T2: T1 + voice(full) + ask + completeness
+// T2: T1 + voice(full) + ask + completeness + context-recovery
 // T3: T2 + repo-mode + search
 // T4: (same as T3 — TEST_FAILURE_TRIAGE is a separate {{}} placeholder, not preamble)
 //
 // Skills by tier:
 //   T1: browse, setup-cookies, benchmark
-//   T2: investigate, cso, retro, doc-release, setup-deploy, canary
+//   T2: investigate, cso, retro, doc-release, setup-deploy, canary, checkpoint, health
 //   T3: autoplan, codex, design-consult, office-hours, ceo/design/eng-review
 //   T4: ship, review, qa, qa-only, design-review, land-deploy
 export function generatePreamble(ctx: TemplateContext): string {
@@ -595,7 +650,7 @@ export function generatePreamble(ctx: TemplateContext): string {
     generateProactivePrompt(ctx),
     generateRoutingInjection(ctx),
     generateVoiceDirective(tier),
-    ...(tier >= 2 ? [generateAskUserFormat(ctx), generateCompletenessSection()] : []),
+    ...(tier >= 2 ? [generateContextRecovery(ctx), generateAskUserFormat(ctx), generateCompletenessSection()] : []),
     ...(tier >= 3 ? [generateRepoModeSection(), generateSearchBeforeBuildingSection(ctx)] : []),
     generateContributorMode(),
     generateCompletionStatus(),