Reduce task query and polling overhead

backend/src/api.ts

@@ -1423,8 +1423,9 @@ async function handleGet(
   }
 
   if (path === "/api/tasks") {
+    const summary = url.searchParams.get("mode") === "summary";
     return jsonResponse(
-      ctx.db.get_all_tasks().map((t) => attachDependencyMetadata(ctx.db, t)),
+      ctx.db.get_all_tasks_with_dependencies(summary),
       200,
       origin,
     );
@@ -1512,7 +1513,7 @@ async function handleGet(
     return jsonResponse({ csrf_token: CSRF_TOKEN }, 200, origin);
   if (path === "/api/health")
     return jsonResponse(
-      { status: "ok", tasks: ctx.db.get_all_tasks().length },
+      { status: "ok", tasks: ctx.db.count_tasks() },
       200,
       origin,
     );

backend/src/db.ts

@@ -106,6 +106,10 @@ export class TaskDB {
     this._migrate("ALTER TABLE tasks ADD COLUMN image_paths TEXT DEFAULT '[]'");
     this._migrate("ALTER TABLE tasks ADD COLUMN notify_slack_channel TEXT");
     this._migrate("ALTER TABLE tasks ADD COLUMN notify_telegram_chat_id TEXT");
+    this.conn.run(`
+      CREATE INDEX IF NOT EXISTS idx_tasks_status_next_run
+      ON tasks(status, next_run_at)
+    `);
 
     this.conn.run(`
       CREATE TABLE IF NOT EXISTS settings (
@@ -174,6 +178,10 @@ export class TaskDB {
       )
     `);
     this._migrate("ALTER TABLE task_runs ADD COLUMN raw_output TEXT");
+    this.conn.run(`
+      CREATE INDEX IF NOT EXISTS idx_task_runs_task_started
+      ON task_runs(task_id, started_at DESC)
+    `);
 
     this.conn.run(`
       CREATE TABLE IF NOT EXISTS heartbeats (
@@ -265,6 +273,10 @@ export class TaskDB {
       CREATE INDEX IF NOT EXISTS idx_task_output_events_timestamp
       ON task_output_events(timestamp)
     `);
+    this.conn.run(`
+      CREATE INDEX IF NOT EXISTS idx_task_output_events_task_timestamp
+      ON task_output_events(task_id, timestamp DESC)
+    `);
 
     // DAG dependency table
     this.conn.run(`
@@ -1286,6 +1298,73 @@ export class TaskDB {
     return rows.map((r) => this._deserialize_task(r));
   }
 
+  /**
+   * Return the task list with dependency metadata using three fixed queries.
+   *
+   * The legacy list keeps the same shape as get_task() plus dependencies and
+   * dependents. Summary mode omits large detail-only columns and truncates the
+   * prompt for TaskCard rendering.
+   */
+  get_all_tasks_with_dependencies(summary: boolean = false): Row[] {
+    const taskSql = summary
+      ? `SELECT id, title, substr(prompt, 1, 240) AS prompt_preview,
+                status, schedule_type, cron_expr, delay_seconds, next_run_at,
+                last_run_at, run_count, max_runs, tags, agent, dag_id
+         FROM tasks ORDER BY created_at DESC`
+      : "SELECT * FROM tasks ORDER BY created_at DESC";
+    const rows = this.conn.query(taskSql).all() as Row[];
+    if (rows.length === 0) return [];
+
+    const taskIds = new Set(rows.map((row) => Number(row["id"])));
+    const dependenciesByTask = new Map<number, Row[]>();
+    const dependentsByTask = new Map<number, number[]>();
+    const dependencies = this.conn
+      .query(
+        `SELECT td.*, t.title AS depends_on_title, t.status AS depends_on_status
+         FROM task_dependencies td
+         JOIN tasks t ON t.id = td.depends_on_task_id`,
+      )
+      .all() as Row[];
+    const dependents = this.conn
+      .query(
+        `SELECT td.*, t.title AS task_title, t.status AS task_status
+         FROM task_dependencies td
+         JOIN tasks t ON t.id = td.task_id`,
+      )
+      .all() as Row[];
+
+    for (const dependency of dependencies) {
+      const taskId = Number(dependency["task_id"]);
+      if (!taskIds.has(taskId)) continue;
+      const value = summary
+        ? { depends_on_task_id: dependency["depends_on_task_id"] }
+        : { ...dependency };
+      const current = dependenciesByTask.get(taskId) ?? [];
+      current.push(value);
+      dependenciesByTask.set(taskId, current);
+    }
+    for (const dependent of dependents) {
+      const upstreamId = Number(dependent["depends_on_task_id"]);
+      if (!taskIds.has(upstreamId)) continue;
+      const current = dependentsByTask.get(upstreamId) ?? [];
+      current.push(Number(dependent["task_id"]));
+      dependentsByTask.set(upstreamId, current);
+    }
+
+    return rows.map((row) => ({
+      ...(summary ? row : this._deserialize_task(row)),
+      dependencies: dependenciesByTask.get(Number(row["id"])) ?? [],
+      dependents: dependentsByTask.get(Number(row["id"])) ?? [],
+    }));
+  }
+
+  count_tasks(): number {
+    const row = this.conn
+      .query("SELECT COUNT(*) AS count FROM tasks")
+      .get() as Row;
+    return Number(row["count"]);
+  }
+
   get_due_tasks(): Row[] {
     const rows = this.conn
       .query(

backend/tests/api-handler.test.ts

@@ -158,6 +158,77 @@ describe("api handler", () => {
     expect(tasks[0]["dependents"]).toEqual([]);
   });
 
+  test("GET /api/tasks batches dependency metadata without per-task queries", async () => {
+    const upstream = db.add_task(
+      makeTask({ title: "Upstream", prompt: "prepare", working_dir: "." }),
+    );
+    const downstream = db.add_task(
+      makeTask({ title: "Downstream", prompt: "finish", working_dir: "." }),
+    );
+    db.add_dependency(downstream, upstream, true);
+    db.get_dependencies = () => {
+      throw new Error("per-task dependency query should not run");
+    };
+    db.get_dependents = () => {
+      throw new Error("per-task dependent query should not run");
+    };
+
+    const tasks = await json(new Request("http://127.0.0.1:9712/api/tasks"));
+
+    expect(tasks).toHaveLength(2);
+    expect(
+      tasks.find((task: Record<string, any>) => task.id === upstream)
+        .dependents,
+    ).toEqual([downstream]);
+    expect(
+      tasks.find((task: Record<string, any>) => task.id === downstream)
+        .dependencies[0],
+    ).toMatchObject({
+      task_id: downstream,
+      depends_on_task_id: upstream,
+      inject_result: 1,
+      depends_on_title: "Upstream",
+    });
+    expect(
+      tasks.find((task: Record<string, any>) => task.id === upstream).prompt,
+    ).toBe("prepare");
+  });
+
+  test("GET /api/tasks summary returns only board fields", async () => {
+    db.add_task(
+      makeTask({
+        title: "Summary",
+        prompt: "x".repeat(400),
+        working_dir: "/private/project",
+      }),
+    );
+
+    const tasks = await json(
+      new Request("http://127.0.0.1:9712/api/tasks?mode=summary"),
+    );
+    const task = tasks[0];
+
+    expect(task.prompt_preview).toHaveLength(240);
+    expect(task.dependencies).toEqual([]);
+    expect(task.dependents).toEqual([]);
+    expect(task).not.toHaveProperty("prompt");
+    expect(task).not.toHaveProperty("working_dir");
+    expect(task).not.toHaveProperty("result");
+    expect(task).not.toHaveProperty("error");
+    expect(task).not.toHaveProperty("prompt_images");
+  });
+
+  test("GET /api/health counts tasks without loading task rows", async () => {
+    db.add_task(makeTask({ title: "Count me", prompt: "p" }));
+    db.get_all_tasks = () => {
+      throw new Error("health should use COUNT");
+    };
+
+    const health = await json(new Request("http://127.0.0.1:9712/api/health"));
+
+    expect(health).toEqual({ status: "ok", tasks: 1 });
+  });
+
   test("GET task output falls back to latest persisted raw output", async () => {
     const created = await json(
       new Request("http://127.0.0.1:9712/api/tasks", {

backend/tests/taskdb.test.ts

@@ -49,6 +49,29 @@ describe("TaskDB", () => {
     expect(db.get_setting("k")).toBe("v2");
   });
 
+  test("test_task_count_and_polling_indexes_are_idempotent", () => {
+    db.add_task(makeTask({ title: "one", prompt: "p" }));
+    expect(db.count_tasks()).toBe(1);
+
+    const dbPath = db.db_path;
+    db.conn.close();
+    db = new TaskDB(dbPath);
+
+    const indexNames = (table: string) =>
+      new Set(
+        (
+          db.conn.query(`PRAGMA index_list('${table}')`).all() as Array<{
+            name: string;
+          }>
+        ).map((row) => row.name),
+      );
+    expect(indexNames("tasks")).toContain("idx_tasks_status_next_run");
+    expect(indexNames("task_runs")).toContain("idx_task_runs_task_started");
+    expect(indexNames("task_output_events")).toContain(
+      "idx_task_output_events_task_timestamp",
+    );
+  });
+
   // ── run history ────────────────────────────────────────────────────────────
   test("test_run_lifecycle_and_ordering", () => {
     const tid = db.add_task(