perf: cheaper ingest — no re-parse of live hooked transcripts, delta hook writes, lighter pollers

- Session sync leaves a transcript alone while hooks feed its session live
  (active, newest event a hook's, touched within DASHBOARD_SYNC_LIVE_HOOK_MS,
  default 5 min) and catches it up once quiet; a hook-created session (which
  importSession skips anyway) is only snapshotted, never parsed.
- Hook writer keeps a per-transcript mark (applied after commit): an
  unchanged TranscriptCache result skips token/compaction/API-error/turn
  writes, a grown one walks only the entries after the last one handled.
- Codex usage: one stamp query per pass instead of one row per journal;
  between full passes (first + every 5 min) only the newest day folders and
  journals written in the last hour are statted; fork parents resolved from
  the table or a full walk.
- Cursor/Antigravity polls back off to 60 s after idle passes
  (server/lib/backoff-poll.js); lane sync runs only while another dashboard
  shares the data dir (checked every 30 s).

server/__tests__/session-sync.test.js

@@ -150,3 +150,85 @@ describe("syncDefaultProjects", () => {
     );
   });
 });
+
+describe("syncDefaultProjects — sessions hooks are feeding", () => {
+  const SNAP_DIR = path.join(process.env.DASHBOARD_DATA_DIR, "transcripts");
+  const more = (sessionId, cwd, ts) => ({
+    type: "assistant",
+    cwd,
+    sessionId,
+    timestamp: ts,
+    message: {
+      model: "claude-opus-4-8",
+      content: [{ type: "text", text: "later" }],
+      usage: { input_tokens: 3, output_tokens: 2 },
+    },
+  });
+  const bumpMtime = (file) => {
+    const future = Date.now() / 1000 + 120;
+    fs.utimesSync(file, future, future);
+  };
+  const ageSession = (id) =>
+    dbModule.db
+      .prepare("UPDATE sessions SET updated_at = ? WHERE id = ?")
+      .run(new Date(Date.now() - 10 * 60_000).toISOString(), id);
+
+  it("defers a live hook-fed imported session, then catches it up once quiet", async () => {
+    const ID = "33333333-cccc-4ccc-8ccc-333333333333";
+    const cache = new Map();
+    const file = writeSession("-live", ID, fixtureLines(ID, "/live"));
+    await syncDefaultProjects(dbModule, { mtimeCache: cache });
+    assert.ok(dbModule.stmts.getSession.get(ID), "imported first");
+
+    // A hook arrives: its event is the newest, and it touches the session.
+    dbModule.stmts.insertEvent.run(ID, `${ID}-main`, "PreToolUse", "Bash", "hook", "{}");
+    dbModule.stmts.touchSession.run(ID);
+    writeSession(
+      "-live",
+      ID,
+      fixtureLines(ID, "/live", [more(ID, "/live", "2026-04-18T12:09:00.000Z")])
+    );
+    bumpMtime(file);
+
+    const live = await syncDefaultProjects(dbModule, { mtimeCache: cache });
+    assert.equal(
+      live.changed.find((c) => c.sessionId === ID),
+      undefined,
+      "deferred while live"
+    );
+    assert.equal(cache.get(file), -1, "kept in the cache so the watcher ignores its appends");
+
+    ageSession(ID); // the hooks went quiet
+    const quiet = await syncDefaultProjects(dbModule, { mtimeCache: cache });
+    assert.ok(
+      quiet.changed.find((c) => c.sessionId === ID && !c.isNew),
+      "caught up once quiet"
+    );
+    assert.notEqual(cache.get(file), -1);
+  });
+
+  it("never re-parses a hook-created session, only refreshes its snapshot once quiet", async () => {
+    const ID = "44444444-dddd-4ddd-8ddd-444444444444";
+    dbModule.stmts.insertSession.run(ID, "hooked", "active", "/hooked", null, null);
+    dbModule.stmts.insertEvent.run(ID, null, "SessionStart", null, "hook", "{}");
+    const file = writeSession("-hooked", ID, fixtureLines(ID, "/hooked"));
+    bumpMtime(file);
+    const snap = path.join(SNAP_DIR, `${ID}.jsonl`);
+    const cache = new Map();
+
+    await syncDefaultProjects(dbModule, { mtimeCache: cache });
+    assert.equal(fs.existsSync(snap), false, "no snapshot copy while hooks are live");
+
+    ageSession(ID);
+    const before = dbModule.db.prepare("SELECT COUNT(*) AS n FROM events WHERE session_id = ?");
+    const n0 = before.get(ID).n;
+    const r = await syncDefaultProjects(dbModule, { mtimeCache: cache });
+    assert.equal(
+      r.changed.find((c) => c.sessionId === ID),
+      undefined,
+      "nothing imported"
+    );
+    assert.equal(before.get(ID).n, n0, "no events written for a hook-created session");
+    assert.equal(fs.existsSync(snap), true, "snapshot taken once quiet");
+  });
+});