feat: preempt active runs in interrupt queue mode

src/gateway/handlers/agent.test.ts

@@ -367,4 +367,64 @@ describe('createAgentHandlers queue policy resolution', () => {
     expect((event.data as { code: number }).code).toBe(3);
     expect((event.data as { queue?: { code: string } }).queue?.code).toBe('overflow');
   });
+
+  it('requests active-session cancellation when interrupt mode receives a new message', async () => {
+    const mockAgent = {
+      process: vi.fn(async () => 'ok'),
+      consumeContextAlert: vi.fn(() => undefined),
+      getContextBudget: vi.fn(() => ({
+        estimatedTokens: 0,
+        contextWindow: 128000,
+        remainingTokens: 128000,
+        usagePct: 0,
+        thresholdPct: 80,
+        thresholdTokens: 102400,
+        shouldCompact: false,
+      })),
+      getUsage: vi.fn(() => ({
+        primary: { inputTokens: 0, outputTokens: 0, calls: 0 },
+        delegation: {},
+        total: { inputTokens: 0, outputTokens: 0, calls: 0, estimatedCost: 0 },
+      })),
+      getModelTier: vi.fn(() => 'default'),
+      setModelTier: vi.fn(),
+      compact: vi.fn(async () => null),
+      reset: vi.fn(),
+    };
+
+    const sessionBridge = {
+      getAgent: vi.fn(() => mockAgent),
+      getSessionId: vi.fn(() => 'ws:s1'),
+      setBusy: vi.fn(),
+      setOnToolUse: vi.fn(),
+      isBusy: vi.fn(() => false),
+      cancelSession: vi.fn(() => true),
+      cancel: vi.fn(() => true),
+    };
+
+    const laneQueue = {
+      enqueue: vi.fn(async (_laneId: string, work: () => Promise<unknown>) => work()),
+      cancel: vi.fn(),
+      isProcessing: vi.fn(() => true),
+    } as unknown as LaneQueue;
+
+    const handlers = createAgentHandlers({
+      sessionBridge: sessionBridge as unknown as AgentHandlerDeps['sessionBridge'],
+      laneQueue,
+      resolveQueuePolicy: vi.fn(() => ({ mode: 'interrupt' as const })),
+    });
+
+    const sent: OutboundMessage[] = [];
+    const send = vi.fn((msg: OutboundMessage) => sent.push(msg));
+
+    await handlers['agent.send']({
+      id: 7,
+      method: 'agent.send',
+      params: { message: 'newest', connectionId: 'conn-1' },
+    }, send);
+
+    expect(sessionBridge.cancelSession).toHaveBeenCalledWith('ws:s1');
+    expect(sessionBridge.cancel).not.toHaveBeenCalled();
+    expect((sent[0] as GatewayEvent).event).toBe('done');
+  });
 });

src/gateway/handlers/agent.ts

@@ -58,6 +58,20 @@ export function createAgentHandlers(deps: AgentHandlerDeps) {
       const laneId = sessionId ?? connectionId;
       const channel = sessionId?.split(':', 1)[0] ?? 'ws';
       const resolvedPolicy = deps.resolveQueuePolicy?.({ laneId, sessionId, connectionId, channel });
+      const laneQueueWithProcessing = deps.laneQueue as LaneQueue & { isProcessing?: (lane: string) => boolean };
+      const laneIsProcessing = typeof laneQueueWithProcessing.isProcessing === 'function'
+        ? laneQueueWithProcessing.isProcessing(laneId)
+        : false;
+
+      // Interrupt mode should preempt active work when a newer request arrives.
+      // LaneQueue itself only rejects queued entries, so we also request agent cancellation.
+      if (resolvedPolicy?.mode === 'interrupt' && laneIsProcessing) {
+        if (sessionId) {
+          deps.sessionBridge.cancelSession(sessionId);
+        } else {
+          deps.sessionBridge.cancel(connectionId);
+        }
+      }
 
       // Enqueue the work — if the lane is idle it runs immediately,
       // otherwise it waits for earlier requests on the same session to finish.

src/gateway/session-bridge.test.ts

@@ -185,6 +185,30 @@ describe('SessionBridge', () => {
     expect(cancelSpy).toHaveBeenCalledTimes(1);
   });
 
+  it('cancelSession requests cancellation when session has a busy connection', () => {
+    const bridge = createBridge();
+    bridge.connect('conn-1');
+    bridge.connect('conn-2');
+    bridge.switchSession('conn-2', 'ws:conn-1');
+
+    const agent = bridge.getAgent('conn-1');
+    if (!agent) {
+      throw new Error('Expected agent for conn-1');
+    }
+    const cancelSpy = vi.spyOn(agent, 'cancel');
+
+    bridge.setBusy('conn-2', true);
+    expect(bridge.cancelSession('ws:conn-1')).toBe(true);
+    expect(cancelSpy).toHaveBeenCalledTimes(1);
+  });
+
+  it('cancelSession returns false when no active operation exists', () => {
+    const bridge = createBridge();
+    bridge.connect('conn-1');
+
+    expect(bridge.cancelSession('ws:conn-1')).toBe(false);
+  });
+
   it('switchSession changes session for a connection', () => {
     const bridge = createBridge();
     bridge.connect('conn-1');

src/gateway/session-bridge.ts

@@ -132,6 +132,30 @@ export class SessionBridge {
     return true;
   }
 
+  /**
+   * Request cancellation for the active operation in a session.
+   * Returns true if at least one connection in the session is currently busy.
+   */
+  cancelSession(sessionId: string): boolean {
+    const clients = Array.from(this.clients.values()).filter((client) => client.sessionId === sessionId);
+    if (clients.length === 0) {
+      return false;
+    }
+
+    const hasBusyClient = clients.some((client) => client.busy);
+    if (!hasBusyClient) {
+      return false;
+    }
+
+    const agent = this.agents.get(sessionId);
+    if (!agent) {
+      return false;
+    }
+
+    agent.cancel();
+    return true;
+  }
+
   /** Set onToolUse callback for a connection's agent. */
   setOnToolUse(connectionId: string, callback: ((event: ToolUseEvent) => void) | undefined): void {
     const client = this.clients.get(connectionId);