diff --git a/apps/desktop/src/hooks/use-local-chat.ts b/apps/desktop/src/hooks/use-local-chat.ts
index 250858b82c..3150917ea6 100644
--- a/apps/desktop/src/hooks/use-local-chat.ts
+++ b/apps/desktop/src/hooks/use-local-chat.ts
@@ -6,7 +6,7 @@
  */
 import { useState, useEffect, useCallback, useRef } from 'react'
 import { useMessagesStore } from '@multica/store'
-import type { ContentBlock } from '@multica/sdk'
+import type { ContentBlock, CompactionEndEvent } from '@multica/sdk'
 
 interface UseLocalChatOptions {
   agentId: string
@@ -86,7 +86,7 @@ export function useLocalChat({ agentId }: UseLocalChatOptions): UseLocalChatRetu
         return
       }
       if (agentEvent.type === 'compaction_end') {
-        const evt = agentEvent as { removed: number; kept: number; tokensRemoved?: number; tokensKept?: number; reason: string }
+        const evt = agentEvent as CompactionEndEvent
         store.endCompaction({
           removed: evt.removed,
           kept: evt.kept,
diff --git a/packages/store/src/connection-store.ts b/packages/store/src/connection-store.ts
index 5ede536a11..bd6893f1fd 100644
--- a/packages/store/src/connection-store.ts
+++ b/packages/store/src/connection-store.ts
@@ -22,6 +22,7 @@ import {
   type ConnectionState,
   type StreamPayload,
   type AgentEvent,
+  type CompactionEndEvent,
   type GetAgentMessagesResult,
   type ContentBlock,
 } from "@multica/sdk"
@@ -148,7 +149,7 @@ function createClient(
             break
           }
           case "compaction_end": {
-            const evt = event as { removed: number; kept: number; tokensRemoved?: number; tokensKept?: number; reason: string }
+            const evt = event as CompactionEndEvent
             store.endCompaction({
               removed: evt.removed,
               kept: evt.kept,
diff --git a/src/agent/events.ts b/src/agent/events.ts
index e0429d5a30..6177b9127b 100644
--- a/src/agent/events.ts
+++ b/src/agent/events.ts
@@ -10,7 +10,13 @@ export type CompactionStartEvent = {
   type: "compaction_start";
 };
 
-/** Emitted when context compaction completes */
+/**
+ * Emitted when context compaction completes.
+ *
+ * Note: `reason` uses a narrow union here for type safety within the agent.
+ * The SDK's `CompactionEndEvent` uses `string` to allow future extensions
+ * without requiring SDK version bumps.
+ */
 export type CompactionEndEvent = {
   type: "compaction_end";
   removed: number;
diff --git a/src/agent/runner.ts b/src/agent/runner.ts
index 261f315f81..a6a1d951b4 100644
--- a/src/agent/runner.ts
+++ b/src/agent/runner.ts
@@ -85,7 +85,8 @@ export class Agent {
   private initialized = false;
 
   // MulticaEvent subscribers (parallel to PiAgentCore's subscriber list)
-  private multicaListeners: Array<(event: MulticaEvent) => void> = [];
+  // Typed as AgentEvent | MulticaEvent to match subscribeAll() callback signature
+  private multicaListeners: Array<(event: AgentEvent | MulticaEvent) => void> = [];
 
   // Auth profile rotation state
   private resolvedProvider: string;
@@ -477,18 +478,28 @@ export class Agent {
     if (!this.session.needsCompaction(messages)) return;
 
     this.emitMulticaEvent({ type: "compaction_start" });
-    const result = await this.session.maybeCompact(messages);
-    if (result?.kept) {
-      this.agent.replaceMessages(result.kept);
+    try {
+      const result = await this.session.maybeCompact(messages);
+      if (result?.kept) {
+        this.agent.replaceMessages(result.kept);
+      }
+      this.emitMulticaEvent({
+        type: "compaction_end",
+        removed: result?.removedCount ?? 0,
+        kept: result?.kept.length ?? messages.length,
+        tokensRemoved: result?.tokensRemoved,
+        tokensKept: result?.tokensKept,
+        reason: result?.reason ?? "tokens",
+      });
+    } catch (err) {
+      this.emitMulticaEvent({
+        type: "compaction_end",
+        removed: 0,
+        kept: messages.length,
+        reason: "tokens",
+      });
+      throw err;
     }
-    this.emitMulticaEvent({
-      type: "compaction_end",
-      removed: result?.removedCount ?? 0,
-      kept: result?.kept.length ?? messages.length,
-      tokensRemoved: result?.tokensRemoved,
-      tokensKept: result?.tokensKept,
-      reason: result?.reason ?? "tokens",
-    });
   }
 
   /**