feat(gateway): support per-channel and per-session queue policy overrides

src/gateway/lane-queue.ts

@@ -47,7 +47,8 @@ export class LaneQueue {
    * Returns a promise that resolves with the work's return value
    * once it has been executed (which may be immediately if the lane is idle).
    */
-  async enqueue<T>(laneId: string, work: () => Promise<T>): Promise<T> {
+  async enqueue<T>(laneId: string, work: () => Promise<T>, policy?: Partial<LaneQueueConfig>): Promise<T> {
+    const effective = this.resolvePolicy(policy);
     let lane = this.lanes.get(laneId);
     if (!lane) {
       lane = { active: false, queue: [] };
@@ -65,12 +66,12 @@ export class LaneQueue {
       }
     }
 
-    if (this.config.mode === 'steer' || this.config.mode === 'interrupt') {
+    if (effective.mode === 'steer' || effective.mode === 'interrupt') {
       this.rejectPending(lane, 'Superseded by newer request');
     }
 
-    if (lane.queue.length >= this.config.cap) {
-      if (this.config.overflow === 'drop_new') {
+    if (lane.queue.length >= effective.cap) {
+      if (effective.overflow === 'drop_new') {
         return Promise.reject(new Error('Lane queue full (drop_new)'));
       }
       // drop_old
@@ -131,6 +132,14 @@ export class LaneQueue {
     }
   }
 
+  private resolvePolicy(policy?: Partial<LaneQueueConfig>): LaneQueueConfig {
+    return {
+      mode: policy?.mode ?? this.config.mode,
+      cap: Math.max(1, policy?.cap ?? this.config.cap),
+      overflow: policy?.overflow ?? this.config.overflow,
+    };
+  }
+
   /**
    * Process the next queued entry for a lane (called after current work finishes).
    * Runs asynchronously so the caller's finally block completes first.