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>

bin/gstack-timeline-read

@@ -0,0 +1,94 @@
+#!/usr/bin/env bash
+# gstack-timeline-read — read and format project timeline
+# Usage: gstack-timeline-read [--since "7 days ago"] [--limit N] [--branch NAME]
+#
+# Session timeline: local-only, never sent anywhere.
+# Reads ~/.gstack/projects/$SLUG/timeline.jsonl, filters, formats.
+# Exit 0 silently if no timeline file exists.
+set -euo pipefail
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+eval "$("$SCRIPT_DIR/gstack-slug" 2>/dev/null)"
+GSTACK_HOME="${GSTACK_HOME:-$HOME/.gstack}"
+
+SINCE=""
+LIMIT=20
+BRANCH=""
+
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    --since) SINCE="$2"; shift 2 ;;
+    --limit) LIMIT="$2"; shift 2 ;;
+    --branch) BRANCH="$2"; shift 2 ;;
+    *) shift ;;
+  esac
+done
+
+TIMELINE_FILE="$GSTACK_HOME/projects/$SLUG/timeline.jsonl"
+
+if [ ! -f "$TIMELINE_FILE" ]; then
+  exit 0
+fi
+
+cat "$TIMELINE_FILE" 2>/dev/null | bun -e "
+const lines = (await Bun.stdin.text()).trim().split('\n').filter(Boolean);
+const since = '${SINCE}';
+const branch = '${BRANCH}';
+const limit = ${LIMIT};
+
+let sinceMs = 0;
+if (since) {
+  // Parse relative time like '7 days ago'
+  const match = since.match(/(\d+)\s*(day|hour|minute|week|month)s?\s*ago/i);
+  if (match) {
+    const n = parseInt(match[1]);
+    const unit = match[2].toLowerCase();
+    const ms = { minute: 60000, hour: 3600000, day: 86400000, week: 604800000, month: 2592000000 };
+    sinceMs = Date.now() - n * (ms[unit] || 86400000);
+  }
+}
+
+const entries = [];
+for (const line of lines) {
+  try {
+    const e = JSON.parse(line);
+    if (sinceMs && new Date(e.ts).getTime() < sinceMs) continue;
+    if (branch && e.branch !== branch) continue;
+    entries.push(e);
+  } catch {}
+}
+
+if (entries.length === 0) process.exit(0);
+
+// Take last N entries
+const recent = entries.slice(-limit);
+
+// Skill counts (completed events only)
+const counts = {};
+const branches = new Set();
+for (const e of entries) {
+  if (e.event === 'completed') {
+    counts[e.skill] = (counts[e.skill] || 0) + 1;
+  }
+  if (e.branch) branches.add(e.branch);
+}
+
+// Output summary
+const countStr = Object.entries(counts)
+  .sort((a, b) => b[1] - a[1])
+  .map(([s, n]) => n + ' /' + s)
+  .join(', ');
+
+if (countStr) {
+  console.log('TIMELINE: ' + countStr + ' across ' + branches.size + ' branch' + (branches.size !== 1 ? 'es' : ''));
+}
+
+// Output recent events
+console.log('');
+console.log('## Recent Events');
+for (const e of recent) {
+  const ts = (e.ts || '').replace('T', ' ').replace(/\.\d+Z$/, 'Z');
+  const dur = e.duration_s ? ' (' + e.duration_s + 's)' : '';
+  const outcome = e.outcome ? ' [' + e.outcome + ']' : '';
+  console.log('- ' + ts + ' /' + e.skill + ' ' + e.event + outcome + dur + (e.branch ? ' on ' + e.branch : ''));
+}
+" 2>/dev/null || exit 0