feat(queue): implement queue scheduler service and API routes

- Added QueueSchedulerService to manage task queue lifecycle, including state machine, dependency resolution, and session management.
- Implemented HTTP API endpoints for queue scheduling:
  - POST /api/queue/execute: Submit items to the scheduler.
  - GET /api/queue/scheduler/state: Retrieve full scheduler state.
  - POST /api/queue/scheduler/start: Start scheduling loop with items.
  - POST /api/queue/scheduler/pause: Pause scheduling.
  - POST /api/queue/scheduler/stop: Graceful stop of the scheduler.
  - POST /api/queue/scheduler/config: Update scheduler configuration.
- Introduced types for queue items, scheduler state, and WebSocket messages to ensure type safety and compatibility with the backend.
- Added static model lists for LiteLLM as a fallback for available models.

ccw/src/core/routes/queue-routes.ts

@@ -0,0 +1,157 @@
+/**
+ * Queue Scheduler Routes Module
+ *
+ * HTTP API endpoints for the Queue Scheduler Service.
+ * Delegates all business logic to QueueSchedulerService.
+ *
+ * API Endpoints:
+ * - POST   /api/queue/execute            - Submit items to the scheduler and start
+ * - GET    /api/queue/scheduler/state     - Get full scheduler state
+ * - POST   /api/queue/scheduler/start     - Start scheduling loop with items
+ * - POST   /api/queue/scheduler/pause     - Pause scheduling
+ * - POST   /api/queue/scheduler/stop      - Graceful stop
+ * - POST   /api/queue/scheduler/config    - Update scheduler configuration
+ */
+
+import type { RouteContext } from './types.js';
+import type { QueueSchedulerService } from '../services/queue-scheduler-service.js';
+import type { QueueItem, QueueSchedulerConfig } from '../../types/queue-types.js';
+
+/**
+ * Handle queue scheduler routes
+ * @returns true if route was handled, false otherwise
+ */
+export async function handleQueueSchedulerRoutes(
+  ctx: RouteContext,
+  schedulerService: QueueSchedulerService,
+): Promise<boolean> {
+  const { pathname, req, res, handlePostRequest } = ctx;
+
+  // POST /api/queue/execute - Submit items and start the scheduler
+  if (pathname === '/api/queue/execute' && req.method === 'POST') {
+    handlePostRequest(req, res, async (body) => {
+      const { items } = body as { items?: QueueItem[] };
+
+      if (!items || !Array.isArray(items) || items.length === 0) {
+        return { error: 'items array is required and must not be empty', status: 400 };
+      }
+
+      try {
+        const state = schedulerService.getState();
+
+        // If idle, start with items; otherwise add items to running scheduler
+        if (state.status === 'idle') {
+          schedulerService.start(items);
+        } else if (state.status === 'running' || state.status === 'paused') {
+          for (const item of items) {
+            schedulerService.addItem(item);
+          }
+        } else {
+          return {
+            error: `Cannot add items when scheduler is in '${state.status}' state`,
+            status: 409,
+          };
+        }
+
+        return {
+          success: true,
+          state: schedulerService.getState(),
+        };
+      } catch (err) {
+        return { error: (err as Error).message, status: 500 };
+      }
+    });
+    return true;
+  }
+
+  // GET /api/queue/scheduler/state - Return full scheduler state
+  if (pathname === '/api/queue/scheduler/state' && req.method === 'GET') {
+    try {
+      const state = schedulerService.getState();
+      res.writeHead(200, { 'Content-Type': 'application/json' });
+      res.end(JSON.stringify({ success: true, state }));
+    } catch (err) {
+      res.writeHead(500, { 'Content-Type': 'application/json' });
+      res.end(JSON.stringify({ error: (err as Error).message }));
+    }
+    return true;
+  }
+
+  // POST /api/queue/scheduler/start - Start scheduling loop with items
+  if (pathname === '/api/queue/scheduler/start' && req.method === 'POST') {
+    handlePostRequest(req, res, async (body) => {
+      const { items } = body as { items?: QueueItem[] };
+
+      if (!items || !Array.isArray(items) || items.length === 0) {
+        return { error: 'items array is required and must not be empty', status: 400 };
+      }
+
+      try {
+        schedulerService.start(items);
+        return {
+          success: true,
+          state: schedulerService.getState(),
+        };
+      } catch (err) {
+        return { error: (err as Error).message, status: 409 };
+      }
+    });
+    return true;
+  }
+
+  // POST /api/queue/scheduler/pause - Pause scheduling
+  if (pathname === '/api/queue/scheduler/pause' && req.method === 'POST') {
+    handlePostRequest(req, res, async () => {
+      try {
+        schedulerService.pause();
+        return {
+          success: true,
+          state: schedulerService.getState(),
+        };
+      } catch (err) {
+        return { error: (err as Error).message, status: 409 };
+      }
+    });
+    return true;
+  }
+
+  // POST /api/queue/scheduler/stop - Graceful stop
+  if (pathname === '/api/queue/scheduler/stop' && req.method === 'POST') {
+    handlePostRequest(req, res, async () => {
+      try {
+        await schedulerService.stop();
+        return {
+          success: true,
+          state: schedulerService.getState(),
+        };
+      } catch (err) {
+        return { error: (err as Error).message, status: 409 };
+      }
+    });
+    return true;
+  }
+
+  // POST /api/queue/scheduler/config - Update scheduler configuration
+  if (pathname === '/api/queue/scheduler/config' && req.method === 'POST') {
+    handlePostRequest(req, res, async (body) => {
+      const config = body as Partial<QueueSchedulerConfig>;
+
+      if (!config || typeof config !== 'object') {
+        return { error: 'Configuration object is required', status: 400 };
+      }
+
+      try {
+        schedulerService.updateConfig(config);
+        return {
+          success: true,
+          config: schedulerService.getState().config,
+        };
+      } catch (err) {
+        return { error: (err as Error).message, status: 500 };
+      }
+    });
+    return true;
+  }
+
+  return false;
+}