feat: Session Intelligence Layer — /checkpoint + /health + context recovery (v0.15.0.0) (#733)

* feat: session timeline binaries (gstack-timeline-log + gstack-timeline-read)

New binaries for the Session Intelligence Layer. gstack-timeline-log appends
JSONL events to ~/.gstack/projects/$SLUG/timeline.jsonl. gstack-timeline-read
reads, filters, and formats timeline data for /retro consumption.

Timeline is local-only project intelligence, never sent anywhere. Always-on
regardless of telemetry setting.

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

* 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>

* feat: /checkpoint + /health skills (Layers 4-5)

/checkpoint: save/resume/list working state snapshots. Supports cross-branch
listing for Conductor workspace handoff. Session duration tracking.

/health: code quality scorekeeper. Wraps project tools (tsc, biome, knip,
shellcheck, tests), computes composite 0-10 score, tracks trends over time.
Auto-detects tools or reads from CLAUDE.md ## Health Stack.

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

* chore: regenerate SKILL.md files + add timeline tests

9 timeline tests (all passing) mirroring learnings.test.ts pattern.
All 34 SKILL.md files regenerated with new preamble (context recovery,
timeline events, routing rules for /checkpoint and /health).

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

* chore: bump version and changelog (v0.15.0.0)

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

* docs: update self-learning roadmap post-Session Intelligence

R1-R3 marked shipped with actual versions. R4 becomes Adaptive Ceremony
(trust as separate policy engine, scope-aware, gradual degradation). R5
becomes /autoship (resumable state machine, not linear chain). R6-R7
unbundled from old R5. Added State Systems reference, Risk Register
(Codex-reviewed), and validation metrics for R4.

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

* test: E2E tests for Session Intelligence (timeline, recovery, checkpoint)

3 gate-tier E2E tests:
- timeline-event-flow: binary data flow round-trip (no LLM)
- context-recovery-artifacts: seeded artifacts appear in preamble
- checkpoint-save-resume: checkpoint file created with YAML frontmatter

Also fixes package.json version sync (0.14.6.0 → 0.15.0.0).

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

---------

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

cso/SKILL.md

@@ -76,6 +76,8 @@ if [ -f "$_LEARN_FILE" ]; then
 else
   echo "LEARNINGS: 0"
 fi
+# Session timeline: record skill start (local-only, never sent anywhere)
+~/.claude/skills/gstack/bin/gstack-timeline-log '{"skill":"cso","event":"started","branch":"'"$_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
@@ -199,6 +201,8 @@ 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"`
@@ -254,6 +258,51 @@ 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?
 
+## 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 "$(~/.claude/skills/gstack/bin/gstack-slug 2>/dev/null)"
+_PROJ="${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.
+
 ## AskUserQuestion Format
 
 **ALWAYS follow this structure for every AskUserQuestion call:**
@@ -342,6 +391,8 @@ 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 analytics (gated on telemetry 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