diff --git a/assistant/src/__tests__/conversation-app-control-lifecycle.test.ts b/assistant/src/__tests__/conversation-app-control-lifecycle.test.ts
new file mode 100644
index 00000000000..dcd59548e86
--- /dev/null
+++ b/assistant/src/__tests__/conversation-app-control-lifecycle.test.ts
@@ -0,0 +1,237 @@
+/**
+ * Lifecycle tests for HostAppControlProxy attachment to a Conversation.
+ *
+ * Verifies that:
+ *  - `setHostAppControlProxy` stores the proxy and disposes any prior proxy
+ *    when replaced with a different instance.
+ *  - `Conversation.dispose()` calls `dispose()` on the attached proxy and
+ *    nulls the field so a subsequent `setHostAppControlProxy(newProxy)`
+ *    cleanly attaches without double-disposing.
+ *
+ * Mirrors the dependency mocking pattern used by
+ * `conversation-lifecycle.test.ts` so we can construct a real Conversation
+ * without bringing up the full daemon stack.
+ */
+
+import { describe, expect, mock, test } from "bun:test";
+
+mock.module("../util/logger.js", () => ({
+  getLogger: () =>
+    new Proxy({} as Record<string, unknown>, { get: () => () => {} }),
+}));
+
+mock.module("../providers/registry.js", () => ({
+  getProvider: () => ({ name: "mock-provider" }),
+  initializeProviders: () => {},
+}));
+
+mock.module("../config/loader.js", () => ({
+  getConfig: () => ({
+    ui: {},
+    llm: {
+      default: {
+        provider: "mock-provider",
+        model: "mock-model",
+        maxTokens: 4096,
+        effort: "max" as const,
+        speed: "standard" as const,
+        temperature: null,
+        thinking: { enabled: false, streamThinking: true },
+        contextWindow: {
+          enabled: true,
+          maxInputTokens: 100000,
+          targetBudgetRatio: 0.3,
+          compactThreshold: 0.8,
+          summaryBudgetRatio: 0.05,
+          overflowRecovery: {
+            enabled: true,
+            safetyMarginRatio: 0.05,
+            maxAttempts: 3,
+            interactiveLatestTurnCompression: "summarize",
+            nonInteractiveLatestTurnCompression: "truncate",
+          },
+        },
+      },
+      profiles: {},
+      callSites: {},
+      pricingOverrides: [],
+    },
+    rateLimit: { maxRequestsPerMinute: 0 },
+  }),
+  loadRawConfig: () => ({}),
+  saveRawConfig: () => {},
+  invalidateConfigCache: () => {},
+}));
+
+mock.module("../prompts/system-prompt.js", () => ({
+  buildSystemPrompt: () => "system prompt",
+}));
+
+mock.module("../permissions/trust-store.js", () => ({
+  clearCache: () => {},
+}));
+
+mock.module("../security/secret-allowlist.js", () => ({
+  resetAllowlist: () => {},
+}));
+
+mock.module("../memory/conversation-crud.js", () => ({
+  updateConversationContextWindow: () => {},
+  deleteMessageById: () => {},
+  updateConversationTitle: () => {},
+  updateConversationUsage: () => {},
+  provenanceFromTrustContext: () => ({
+    source: "user",
+    trustContext: undefined,
+  }),
+  getConversationOriginInterface: () => null,
+  getConversationOriginChannel: () => null,
+  getMessages: () => [],
+  getConversation: () => null,
+  createConversation: () => ({ id: "conv-app-control" }),
+  addMessage: async () => ({ id: "persisted-1" }),
+  setConversationOriginChannelIfUnset: () => {},
+  setConversationOriginInterfaceIfUnset: () => {},
+}));
+
+mock.module("../memory/conversation-queries.js", () => ({
+  listConversations: () => [],
+}));
+
+// Stub graph_extract / auto-analysis enqueue paths so dispose's best-effort
+// background work doesn't reach into real subsystems during the test.
+mock.module("../memory/jobs-store.js", () => ({
+  enqueueMemoryJob: () => {},
+}));
+
+mock.module("../memory/auto-analysis-enqueue.js", () => ({
+  enqueueAutoAnalysisIfEnabled: () => {},
+}));
+
+mock.module("../memory/auto-analysis-guard.js", () => ({
+  isAutoAnalysisConversation: () => false,
+}));
+
+import { Conversation } from "../daemon/conversation.js";
+import type { HostAppControlProxy } from "../daemon/host-app-control-proxy.js";
+
+/**
+ * Minimal stand-in for HostAppControlProxy that records dispose() calls.
+ * The Conversation only invokes `dispose()` on the proxy in the lifecycle
+ * paths under test, so we don't need the rest of the API.
+ */
+function makeFakeProxy(): {
+  proxy: HostAppControlProxy;
+  disposeCount: () => number;
+} {
+  let disposed = 0;
+  const fake = {
+    dispose() {
+      disposed++;
+    },
+  } as unknown as HostAppControlProxy;
+  return { proxy: fake, disposeCount: () => disposed };
+}
+
+function makeConversation(): Conversation {
+  const provider = {
+    name: "mock",
+    sendMessage: async () => ({
+      content: [],
+      model: "mock",
+      usage: { inputTokens: 0, outputTokens: 0 },
+      stopReason: "end_turn",
+    }),
+  };
+  const conv = new Conversation(
+    "conv-app-control",
+    provider,
+    "system prompt",
+    4096,
+    () => {},
+    "/tmp",
+  );
+  conv.setTrustContext({ trustClass: "guardian", sourceChannel: "vellum" });
+  return conv;
+}
+
+describe("Conversation — HostAppControlProxy lifecycle", () => {
+  test("setHostAppControlProxy stores the proxy", () => {
+    const conversation = makeConversation();
+    const { proxy, disposeCount } = makeFakeProxy();
+
+    conversation.setHostAppControlProxy(proxy);
+
+    expect(conversation.hostAppControlProxy).toBe(proxy);
+    expect(disposeCount()).toBe(0);
+  });
+
+  test("setHostAppControlProxy disposes prior proxy when replaced", () => {
+    const conversation = makeConversation();
+    const first = makeFakeProxy();
+    const second = makeFakeProxy();
+
+    conversation.setHostAppControlProxy(first.proxy);
+    conversation.setHostAppControlProxy(second.proxy);
+
+    expect(first.disposeCount()).toBe(1);
+    expect(second.disposeCount()).toBe(0);
+    expect(conversation.hostAppControlProxy).toBe(second.proxy);
+  });
+
+  test("setHostAppControlProxy with the same instance does not redispose", () => {
+    const conversation = makeConversation();
+    const { proxy, disposeCount } = makeFakeProxy();
+
+    conversation.setHostAppControlProxy(proxy);
+    conversation.setHostAppControlProxy(proxy);
+
+    expect(disposeCount()).toBe(0);
+    expect(conversation.hostAppControlProxy).toBe(proxy);
+  });
+
+  test("setHostAppControlProxy(undefined) disposes the existing proxy", () => {
+    const conversation = makeConversation();
+    const { proxy, disposeCount } = makeFakeProxy();
+
+    conversation.setHostAppControlProxy(proxy);
+    conversation.setHostAppControlProxy(undefined);
+
+    expect(disposeCount()).toBe(1);
+    expect(conversation.hostAppControlProxy).toBeUndefined();
+  });
+
+  test("Conversation.dispose() disposes the attached proxy and nulls the field", () => {
+    const conversation = makeConversation();
+    const { proxy, disposeCount } = makeFakeProxy();
+
+    conversation.setHostAppControlProxy(proxy);
+    conversation.dispose();
+
+    expect(disposeCount()).toBe(1);
+    expect(conversation.hostAppControlProxy).toBeUndefined();
+  });
+
+  test("Conversation.dispose() is a no-op when no proxy is attached", () => {
+    const conversation = makeConversation();
+
+    expect(() => conversation.dispose()).not.toThrow();
+    expect(conversation.hostAppControlProxy).toBeUndefined();
+  });
+
+  test("setHostAppControlProxy after dispose cleanly attaches without double-disposing the prior proxy", () => {
+    const conversation = makeConversation();
+    const first = makeFakeProxy();
+    const second = makeFakeProxy();
+
+    conversation.setHostAppControlProxy(first.proxy);
+    conversation.dispose();
+    // After dispose the field is nulled, so attaching a new proxy must NOT
+    // call dispose() on the (already-disposed) prior proxy a second time.
+    conversation.setHostAppControlProxy(second.proxy);
+
+    expect(first.disposeCount()).toBe(1);
+    expect(second.disposeCount()).toBe(0);
+    expect(conversation.hostAppControlProxy).toBe(second.proxy);
+  });
+});
diff --git a/assistant/src/daemon/conversation.ts b/assistant/src/daemon/conversation.ts
index 3c21f4ad854..ba2ad0edba1 100644
--- a/assistant/src/daemon/conversation.ts
+++ b/assistant/src/daemon/conversation.ts
@@ -206,9 +206,10 @@ export class Conversation {
   /** @internal */ callSessionId?: string;
   /** @internal */ hostCuProxy?: HostCuProxy;
   /**
-   * Per-conversation host app-control proxy (full lifecycle wiring lands
-   * in PR 10). Declared here so the `/v1/host-app-control-result` route
-   * can forward result payloads to the awaiting promise.
+   * Per-conversation host app-control proxy. Set via
+   * `setHostAppControlProxy` and disposed in `dispose()`. The
+   * `/v1/host-app-control-result` route forwards result payloads to the
+   * awaiting promise via this reference.
    * @internal
    */
   hostAppControlProxy?: HostAppControlProxy;
@@ -763,9 +764,12 @@ export class Conversation {
       clearTimeout(timer);
     }
     this.recentlyCompletedStandaloneSurfaces.clear();
-    // Only dispose the per-conversation CU proxy. Bash/File/Transfer are
-    // singletons — their lifecycle is managed by static disposeInstance().
+    // Only dispose the per-conversation CU and app-control proxies.
+    // Bash/File/Transfer are singletons — their lifecycle is managed by
+    // static disposeInstance().
     this.hostCuProxy?.dispose();
+    this.hostAppControlProxy?.dispose();
+    this.hostAppControlProxy = undefined;
     // CES client is owned by DaemonServer — just drop the reference.
     // Do NOT close it here; the server manages the CES lifecycle.
     this.cesClient = undefined;
@@ -944,6 +948,13 @@ export class Conversation {
     this.hostCuProxy = proxy;
   }
 
+  setHostAppControlProxy(proxy: HostAppControlProxy | undefined): void {
+    if (this.hostAppControlProxy && this.hostAppControlProxy !== proxy) {
+      this.hostAppControlProxy.dispose();
+    }
+    this.hostAppControlProxy = proxy;
+  }
+
   // ── Server-authoritative state signals ─────────────────────────────
 
   emitConfirmationStateChanged(