feat(agent): add AgentErrorEvent for error propagation via subscribe

Add agent_error event type to MulticaEvent union so errors from
agent runs reach subscribe() consumers (Desktop IPC + Channel).
Make emitMulticaEvent public on Runner so AsyncAgent can emit errors.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/agent/async-agent.ts

@@ -48,12 +48,16 @@ export class AsyncAgent {
         await this.agent.flushSession();
         // Normal text is delivered via message_end event; only handle errors here
         if (result.error) {
+          console.error(`[AsyncAgent] Agent run error: ${result.error}`);
           this.channel.send({ id: uuidv7(), content: `[error] ${result.error}` });
+          this.agent.emitMulticaEvent({ type: "agent_error", error: result.error });
         }
       })
       .catch((err) => {
         const message = err instanceof Error ? err.message : String(err);
+        console.error(`[AsyncAgent] Agent run exception: ${message}`);
         this.channel.send({ id: uuidv7(), content: `[error] ${message}` });
+        this.agent.emitMulticaEvent({ type: "agent_error", error: message });
       });
   }
 

src/agent/events.ts

@@ -26,5 +26,11 @@ export type CompactionEndEvent = {
   reason: "count" | "tokens" | "summary" | "pruning";
 };
 
+/** Emitted when the agent encounters an error (LLM failure, quota exceeded, etc.) */
+export type AgentErrorEvent = {
+  type: "agent_error";
+  error: string;
+};
+
 /** Union of all Multica-specific events */
-export type MulticaEvent = CompactionStartEvent | CompactionEndEvent;
+export type MulticaEvent = CompactionStartEvent | CompactionEndEvent | AgentErrorEvent;

src/agent/runner.ts

@@ -342,7 +342,7 @@ export class Agent {
     };
   }
 
-  private emitMulticaEvent(event: MulticaEvent): void {
+  emitMulticaEvent(event: MulticaEvent): void {
     for (const fn of this.multicaListeners) {
       try {
         fn(event);