feat: Auto-resume idle agents for inter-agent conversations

When an agent asks a question via `cw ask` targeting an idle agent,
the conversation router now auto-resumes the idle agent's session so
it can answer. Previously, questions to idle agents sat unanswered
forever because target resolution only matched running agents.

Changes:
- Add `resumeForConversation()` to AgentManager interface and implement
  on MultiProviderAgentManager (mirrors resumeForCommit pattern)
- Relax createConversation target resolution: prefer running, fall back
  to idle (was running-only)
- Trigger auto-resume after conversation creation for idle targets
- Add concurrency lock (conversationResumeLocks Set) to prevent
  double-resume race conditions

apps/server/agent/mock-manager.ts

@@ -471,6 +471,42 @@ export class MockAgentManager implements AgentManager {
     record.info.updatedAt = now;
   }
 
+  /**
+   * Resume an idle agent to answer an inter-agent conversation.
+   * Mock implementation: marks agent as running and schedules immediate completion.
+   */
+  async resumeForConversation(
+    agentId: string,
+    conversationId: string,
+    question: string,
+    fromAgentId: string,
+  ): Promise<boolean> {
+    const record = this.agents.get(agentId);
+    if (!record || record.info.status !== 'idle' || !record.info.sessionId) {
+      return false;
+    }
+
+    record.info.status = 'running';
+    record.info.updatedAt = new Date();
+
+    if (this.eventBus) {
+      const event: AgentResumedEvent = {
+        type: 'agent:resumed',
+        timestamp: new Date(),
+        payload: {
+          agentId,
+          name: record.info.name,
+          taskId: record.info.taskId,
+          sessionId: record.info.sessionId,
+        },
+      };
+      this.eventBus.emit(event);
+    }
+
+    this.scheduleCompletion(agentId, { status: 'done', delay: 0, result: 'Answered conversation' });
+    return true;
+  }
+
   /**
    * Clear all agents and pending timers.
    * Useful for test cleanup.

apps/server/agent/types.ts

@@ -237,4 +237,24 @@ export interface AgentManager {
    * @param agentId - Agent to dismiss
    */
   dismiss(agentId: string): Promise<void>;
+
+  /**
+   * Resume an idle agent to answer an inter-agent conversation.
+   *
+   * When Agent A asks Agent B a question via `cw ask` and Agent B is idle,
+   * this resumes B's session with a prompt to answer via `cw answer` and
+   * drain any remaining pending conversations via `cw listen`.
+   *
+   * @param agentId - The idle agent to resume
+   * @param conversationId - The conversation that triggered the resume
+   * @param question - The question being asked
+   * @param fromAgentId - The agent asking the question
+   * @returns true if resume was initiated, false if not possible
+   */
+  resumeForConversation(
+    agentId: string,
+    conversationId: string,
+    question: string,
+    fromAgentId: string,
+  ): Promise<boolean>;
 }