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>

test/helpers/touchfiles.ts

@@ -107,6 +107,11 @@ export const E2E_TOUCHFILES: Record<string, string[]> = {
   // Learnings
   'learnings-show': ['learn/**', 'bin/gstack-learnings-search', 'bin/gstack-learnings-log', 'scripts/resolvers/learnings.ts'],
 
+  // Session Intelligence (timeline, context recovery, checkpoint)
+  'timeline-event-flow':         ['bin/gstack-timeline-log', 'bin/gstack-timeline-read'],
+  'context-recovery-artifacts':  ['scripts/resolvers/preamble.ts', 'bin/gstack-timeline-log', 'bin/gstack-slug', 'learn/**'],
+  'checkpoint-save-resume':      ['checkpoint/**', 'bin/gstack-slug'],
+
   // Document-release
   'document-release': ['document-release/**'],
 
@@ -241,6 +246,11 @@ export const E2E_TIERS: Record<string, 'gate' | 'periodic'> = {
   'codex-offered-design-review': 'gate',
   'codex-offered-eng-review': 'gate',
 
+  // Session Intelligence — gate for data flow, periodic for agent integration
+  'timeline-event-flow': 'gate',            // Binary data flow (no LLM needed)
+  'context-recovery-artifacts': 'gate',     // Preamble reads seeded artifacts
+  'checkpoint-save-resume': 'gate',         // Checkpoint round-trip
+
   // Ship — gate (end-to-end ship path)
   'ship-base-branch': 'gate',
   'ship-local-workflow': 'gate',