feat: add per-project message trigger wait queue

- TriggerQueue: FIFO per-project queue, max 5 items, 5min TTL expiry
- Replace reject-when-locked with queue: users get position feedback
- Run completion auto-starts next queued trigger (skips expired items)
- /reset clears project queue; 60s periodic purge interval
- Add unit tests (10) for queue lifecycle and edge cases

hub/src/feishu/triggerQueue.ts

@@ -0,0 +1,100 @@
+import type { MessageReceiveEvent } from "./client.js";
+
+export interface QueuedTrigger {
+  readonly projectId: string;
+  readonly chatId: string;
+  readonly prompt: string;
+  readonly msg: MessageReceiveEvent["message"];
+  readonly senderOpenId: string;
+  readonly actor: { readonly feishuOpenId: string; readonly chatId: string };
+  readonly enqueuedAt: number;
+}
+
+export interface TriggerQueueOptions {
+  readonly maxQueueSize?: number;
+  readonly maxWaitMs?: number;
+}
+
+const DEFAULT_MAX_QUEUE_SIZE = 5;
+const DEFAULT_MAX_WAIT_MS = 300_000;
+
+export class TriggerQueue {
+  readonly maxQueueSize: number;
+  readonly maxWaitMs: number;
+
+  private readonly queues = new Map<string, QueuedTrigger[]>();
+
+  constructor(options: TriggerQueueOptions = {}) {
+    this.maxQueueSize = Math.max(0, Math.trunc(options.maxQueueSize ?? DEFAULT_MAX_QUEUE_SIZE));
+    this.maxWaitMs = Math.max(0, Math.trunc(options.maxWaitMs ?? DEFAULT_MAX_WAIT_MS));
+  }
+
+  enqueue(projectId: string, trigger: Omit<QueuedTrigger, "projectId" | "enqueuedAt">): number {
+    const queue = this.queues.get(projectId) ?? [];
+    if (queue.length >= this.maxQueueSize) return 0;
+
+    queue.push({
+      ...trigger,
+      projectId,
+      enqueuedAt: Date.now(),
+    });
+    if (!this.queues.has(projectId)) {
+      this.queues.set(projectId, queue);
+    }
+    return queue.length;
+  }
+
+  dequeue(projectId: string): QueuedTrigger | null {
+    const queue = this.queues.get(projectId);
+    if (queue === undefined || queue.length === 0) return null;
+
+    const next = queue.shift() ?? null;
+    if (queue.length === 0) {
+      this.queues.delete(projectId);
+    }
+    return next;
+  }
+
+  peek(projectId: string): QueuedTrigger | null {
+    return this.queues.get(projectId)?.[0] ?? null;
+  }
+
+  length(projectId: string): number {
+    return this.queues.get(projectId)?.length ?? 0;
+  }
+
+  hasPending(projectId: string): boolean {
+    return this.length(projectId) > 0;
+  }
+
+  purgeExpired(): number {
+    const now = Date.now();
+    let removed = 0;
+    for (const [projectId, queue] of this.queues) {
+      const fresh = queue.filter((trigger) => !this.isExpired(trigger, now));
+      removed += queue.length - fresh.length;
+      if (fresh.length === 0) {
+        this.queues.delete(projectId);
+      } else if (fresh.length !== queue.length) {
+        this.queues.set(projectId, fresh);
+      }
+    }
+    return removed;
+  }
+
+  clear(projectId: string): number {
+    const count = this.length(projectId);
+    this.queues.delete(projectId);
+    return count;
+  }
+
+  clearAll(): void {
+    this.queues.clear();
+  }
+
+  isExpired(trigger: QueuedTrigger, now = Date.now()): boolean {
+    return trigger.enqueuedAt + this.maxWaitMs < now;
+  }
+}
+
+export const triggerQueue = new TriggerQueue();