feat(cockpit): quick wins — sync chip, cost budget guard, digest, recent commits (W3)

Four small, high-delight features that turn passive capture into glanceable signals.

- Sync chip on project cards: ahead/behind vs upstream + last-commit time, folded
  into the existing concurrent per-repo metadata pass (git rev-list --count
  --left-right @{u}...HEAD + git log -1 --format=%ct; no upstream → undefined, no route).
- Cost budget guard: COST_BUDGET_USD env (0 = off); a per-session one-shot latch
  (Session.budgetNotified, cost is monotonic so never re-armed) fires a single push
  on threshold crossing in manager.handleStatusLine; the already-broadcast telemetry
  frame carries the warn (tg-cost-warn styling derived from costUsd>=budget via
  /config/ui — no new ServerMessage). web-push title added to sw-push.js.
- "While you were away" digest: GET /digest?since= → {finished, needsInput, stuck,
  totalCostUsd, sessions[]} aggregate over manager.list(); FE banner on reconnect.
- Recent commits per project: src/http/git-log.ts (NUL-delimited git log → CommitInfo[]),
  GET /projects/log?path= (isValidGitDir), textContent-inert render in project detail.

All git via execFile (no shell) + validated cwd; new routes read-only; commit
messages rendered via textContent. Verified: typecheck + build:web clean, 1904 pass
at --test-timeout=30000 (two default-5s failures are slow-sandbox real-subprocess
timeout flakes — the known ring-buffer test + a new real-git-clone sync test — not
logic regressions).

test/telemetry-gauge.test.ts

@@ -129,6 +129,36 @@ describe('renderTelemetryGauge', () => {
     expect(c.querySelector('.tg-cost')).toBeNull()
   })
 
+  // ── cost budget warn (W3 b) ──
+
+  it('adds tg-cost-warn when costUsd >= costBudgetUsd', () => {
+    const c = makeContainer()
+    renderTelemetryGauge(c, makeTelemetry({ costUsd: 6 }), 30_000, 5)
+    expect(c.querySelector('.tg-cost')?.classList.contains('tg-cost-warn')).toBe(true)
+  })
+
+  it('adds tg-cost-warn exactly at the budget boundary (>=)', () => {
+    const c = makeContainer()
+    renderTelemetryGauge(c, makeTelemetry({ costUsd: 5 }), 30_000, 5)
+    expect(c.querySelector('.tg-cost')?.classList.contains('tg-cost-warn')).toBe(true)
+  })
+
+  it('does NOT add tg-cost-warn when costUsd < budget', () => {
+    const c = makeContainer()
+    renderTelemetryGauge(c, makeTelemetry({ costUsd: 3 }), 30_000, 5)
+    expect(c.querySelector('.tg-cost')?.classList.contains('tg-cost-warn')).toBe(false)
+  })
+
+  it('does NOT add tg-cost-warn when budget is 0 or undefined', () => {
+    const c1 = makeContainer()
+    renderTelemetryGauge(c1, makeTelemetry({ costUsd: 6 }), 30_000, 0)
+    expect(c1.querySelector('.tg-cost')?.classList.contains('tg-cost-warn')).toBe(false)
+
+    const c2 = makeContainer()
+    renderTelemetryGauge(c2, makeTelemetry({ costUsd: 6 }), 30_000)
+    expect(c2.querySelector('.tg-cost')?.classList.contains('tg-cost-warn')).toBe(false)
+  })
+
   // ── model chip ──
 
   it('renders model chip when model is present', () => {