diff --git a/extensions/acpx/src/runtime-internals/events.test.ts b/extensions/acpx/src/runtime-internals/events.test.ts
index bb8067c3327..6358cf339ca 100644
--- a/extensions/acpx/src/runtime-internals/events.test.ts
+++ b/extensions/acpx/src/runtime-internals/events.test.ts
@@ -67,6 +67,37 @@ describe("parsePromptEventLine", () => {
     });
   });
 
+  it("parses JSON-RPC result stopReason as done", () => {
+    const line = JSON.stringify({
+      jsonrpc: "2.0",
+      id: 3,
+      result: {
+        stopReason: "end_turn",
+      },
+    });
+    expect(parsePromptEventLine(line)).toEqual({
+      type: "done",
+      stopReason: "end_turn",
+    });
+  });
+
+  it("parses JSON-RPC errors as runtime errors", () => {
+    const line = JSON.stringify({
+      jsonrpc: "2.0",
+      id: 2,
+      error: {
+        code: -32002,
+        message: "Resource not found",
+      },
+    });
+    expect(parsePromptEventLine(line)).toEqual({
+      type: "error",
+      message: "Resource not found",
+      code: undefined,
+      retryable: undefined,
+    });
+  });
+
   it("keeps compatibility with simplified text/done lines", () => {
     expect(parsePromptEventLine(JSON.stringify({ type: "text", content: "alpha" }))).toEqual({
       type: "text_delta",
diff --git a/extensions/acpx/src/runtime-internals/events.ts b/extensions/acpx/src/runtime-internals/events.ts
index ac5f91acd5a..eef615dae02 100644
--- a/extensions/acpx/src/runtime-internals/events.ts
+++ b/extensions/acpx/src/runtime-internals/events.ts
@@ -65,6 +65,28 @@ function resolveStructuredPromptPayload(parsed: Record<string, unknown>): {
     }
   }
 
+  const result = parsed.result;
+  if (isRecord(result)) {
+    const stopReason = asTrimmedString(result.stopReason);
+    if (stopReason) {
+      return {
+        type: "done",
+        payload: result,
+      };
+    }
+  }
+
+  const rpcError = parsed.error;
+  if (isRecord(rpcError)) {
+    const message = asTrimmedString(rpcError.message);
+    if (message) {
+      return {
+        type: "error",
+        payload: rpcError,
+      };
+    }
+  }
+
   const sessionUpdate = asOptionalString(parsed.sessionUpdate) as AcpSessionUpdateTag | undefined;
   if (sessionUpdate) {
     return {
diff --git a/src/acp/translator.session-rate-limit.test.ts b/src/acp/translator.session-rate-limit.test.ts
index 566b61a5027..be8a39a31f7 100644
--- a/src/acp/translator.session-rate-limit.test.ts
+++ b/src/acp/translator.session-rate-limit.test.ts
@@ -91,12 +91,28 @@ function createToolEvent(params: {
   } as unknown as EventFrame;
 }
 
-function createChatFinalEvent(sessionKey: string): EventFrame {
+function createChatFinalEvent(
+  sessionKey: string,
+  params: {
+    text?: string;
+    stopReason?: string;
+  } = {},
+): EventFrame {
   return {
     event: "chat",
     payload: {
       sessionKey,
       state: "final",
+      ...(params.stopReason ? { stopReason: params.stopReason } : {}),
+      ...(params.text
+        ? {
+            message: {
+              role: "assistant",
+              content: [{ type: "text", text: params.text }],
+              timestamp: Date.now(),
+            },
+          }
+        : {}),
     },
   } as unknown as EventFrame;
 }
@@ -881,6 +897,39 @@ describe("acp tool streaming bridge behavior", () => {
 });
 
 describe("acp session metadata and usage updates", () => {
+  it("flushes final assistant text from chat.final message payload before resolving prompt", async () => {
+    const sessionStore = createInMemorySessionStore();
+    const connection = createAcpConnection();
+    const sessionUpdate = connection.__sessionUpdateMock;
+    const request = vi.fn(async (method: string) => {
+      if (method === "chat.send") {
+        return new Promise(() => {});
+      }
+      return { ok: true };
+    }) as GatewayClient["request"];
+    const agent = new AcpGatewayAgent(connection, createAcpGateway(request), {
+      sessionStore,
+    });
+
+    await agent.loadSession(createLoadSessionRequest("usage-session"));
+    sessionUpdate.mockClear();
+
+    const promptPromise = agent.prompt(createPromptRequest("usage-session", "hello"));
+
+    await agent.handleGatewayEvent(createChatFinalEvent("usage-session", { text: "final answer" }));
+
+    await expect(promptPromise).resolves.toEqual({ stopReason: "end_turn" });
+    expect(sessionUpdate).toHaveBeenCalledWith({
+      sessionId: "usage-session",
+      update: {
+        sessionUpdate: "agent_message_chunk",
+        content: { type: "text", text: "final answer" },
+      },
+    });
+
+    sessionStore.clearAllSessionsForTest();
+  });
+
   it("emits a fresh usage snapshot after prompt completion when gateway totals are available", async () => {
     const sessionStore = createInMemorySessionStore();
     const connection = createAcpConnection();
diff --git a/src/acp/translator.ts b/src/acp/translator.ts
index 8ab1f821fc8..061fe8b72f1 100644
--- a/src/acp/translator.ts
+++ b/src/acp/translator.ts
@@ -812,6 +812,9 @@ export class AcpGatewayAgent implements Agent {
     }
 
     if (state === "final") {
+      if (messageData) {
+        await this.handleDeltaEvent(pending.sessionId, messageData);
+      }
       const rawStopReason = payload.stopReason as string | undefined;
       const stopReason: StopReason = rawStopReason === "max_tokens" ? "max_tokens" : "end_turn";
       await this.finishPrompt(pending.sessionId, pending, stopReason);