diff --git a/ui/goose2/src/features/chat/hooks/__tests__/useChat.attachments.test.ts b/ui/goose2/src/features/chat/hooks/__tests__/useChat.attachments.test.ts
index da14807a07..d22e640e9d 100644
--- a/ui/goose2/src/features/chat/hooks/__tests__/useChat.attachments.test.ts
+++ b/ui/goose2/src/features/chat/hooks/__tests__/useChat.attachments.test.ts
@@ -95,12 +95,12 @@ describe("useChat attachments", () => {
     expect(mockAcpSendMessage).toHaveBeenCalledWith(
       "session-1",
       "Attached items:\n- [file] /tmp/report.pdf\n- [directory] /tmp/screenshots\nPlease review these",
-      {
+      expect.objectContaining({
         systemPrompt: undefined,
         personaId: undefined,
         personaName: undefined,
         images: undefined,
-      },
+      }),
     );
   });
 
@@ -146,12 +146,12 @@ describe("useChat attachments", () => {
     expect(mockAcpSendMessage).toHaveBeenCalledWith(
       "session-1",
       "Attached items:\n- [image] diagram.png (image attached)\n ",
-      {
+      expect.objectContaining({
         systemPrompt: undefined,
         personaId: undefined,
         personaName: undefined,
         images: [["abc123", "image/png"]],
-      },
+      }),
     );
   });
 
@@ -193,12 +193,12 @@ describe("useChat attachments", () => {
     expect(mockAcpSendMessage).toHaveBeenCalledWith(
       "session-1",
       "Attached items:\n- [file] /tmp/mobile-confirmation.html\n- [directory] /tmp/neighborhood block\n- [image] Screenshot 2026-04-09 at 1.25.32 PM.png (image attached)\ncan you see the attachments i attached?",
-      {
+      expect.objectContaining({
         systemPrompt: undefined,
         personaId: undefined,
         personaName: undefined,
         images: [["abc123", "image/png"]],
-      },
+      }),
     );
   });
 
@@ -233,12 +233,12 @@ describe("useChat attachments", () => {
     expect(mockAcpSendMessage).toHaveBeenCalledWith(
       "session-1",
       "Attached items:\n- [file] report.pdf\nPlease review this",
-      {
+      expect.objectContaining({
         systemPrompt: undefined,
         personaId: undefined,
         personaName: undefined,
         images: undefined,
-      },
+      }),
     );
   });
 });
diff --git a/ui/goose2/src/features/chat/hooks/__tests__/useChat.test.ts b/ui/goose2/src/features/chat/hooks/__tests__/useChat.test.ts
index bbe9009125..d46cdbef7b 100644
--- a/ui/goose2/src/features/chat/hooks/__tests__/useChat.test.ts
+++ b/ui/goose2/src/features/chat/hooks/__tests__/useChat.test.ts
@@ -127,12 +127,14 @@ describe("useChat", () => {
       result.current.stopGeneration();
     });
 
-    expect(mockAcpSendMessage).toHaveBeenCalledWith("session-1", "Hello", {
-      systemPrompt: undefined,
-      personaId: "persona-b",
-      personaName: "Persona B",
-      images: undefined,
-    });
+    expect(mockAcpSendMessage).toHaveBeenCalledWith("session-1", "Hello",
+      expect.objectContaining({
+        systemPrompt: undefined,
+        personaId: "persona-b",
+        personaName: "Persona B",
+        images: undefined,
+      }),
+    );
     expect(mockAcpCancelSession).toHaveBeenCalledWith("session-1", "persona-b");
 
     deferred.resolve();
@@ -313,23 +315,23 @@ describe("useChat", () => {
       1,
       "session-1",
       "First",
-      {
+      expect.objectContaining({
         systemPrompt: undefined,
         personaId: undefined,
         personaName: undefined,
         images: undefined,
-      },
+      }),
     );
     expect(mockAcpSendMessage).toHaveBeenNthCalledWith(
       2,
       "session-2",
       "Second",
-      {
+      expect.objectContaining({
         systemPrompt: undefined,
         personaId: undefined,
         personaName: undefined,
         images: undefined,
-      },
+      }),
     );
 
     deferred.resolve();
@@ -366,12 +368,14 @@ describe("useChat", () => {
       personaId: undefined,
     });
     expect(mockAcpSetModel).toHaveBeenCalledWith("session-1", "gpt-4.1");
-    expect(mockAcpSendMessage).toHaveBeenCalledWith("session-1", "Hello", {
-      systemPrompt: undefined,
-      personaId: undefined,
-      personaName: undefined,
-      images: undefined,
-    });
+    expect(mockAcpSendMessage).toHaveBeenCalledWith("session-1", "Hello",
+      expect.objectContaining({
+        systemPrompt: undefined,
+        personaId: undefined,
+        personaName: undefined,
+        images: undefined,
+      }),
+    );
   });
 
   it("appends an error message and removes the empty assistant placeholder when send fails", async () => {
diff --git a/ui/goose2/src/features/chat/hooks/useChat.ts b/ui/goose2/src/features/chat/hooks/useChat.ts
index 7db196b364..86736a00dd 100644
--- a/ui/goose2/src/features/chat/hooks/useChat.ts
+++ b/ui/goose2/src/features/chat/hooks/useChat.ts
@@ -244,6 +244,7 @@ export function useChat(
             (img) => [img.base64, img.mimeType] as [string, string],
           ),
           truncateBeforeMessageId,
+          messageId: userMessage.id,
         });
 
         store.setChatState(sessionId, "idle");
diff --git a/ui/goose2/src/shared/api/acp.ts b/ui/goose2/src/shared/api/acp.ts
index c2f23ee4e4..1d94f9089b 100644
--- a/ui/goose2/src/shared/api/acp.ts
+++ b/ui/goose2/src/shared/api/acp.ts
@@ -22,6 +22,10 @@ export interface AcpSendMessageOptions {
    *  from both the display log and LLM context before appending the new prompt.
    *  Used by edit and retry to rewind the conversation. */
   truncateBeforeMessageId?: string;
+  /** Pre-generated message ID to use for this user message.  When provided the
+   *  same ID is registered with the notification handler and sent to the
+   *  backend so the frontend store and backend thread_messages stay in sync. */
+  messageId?: string;
 }
 
 export interface AcpPrepareSessionOptions {
@@ -63,7 +67,7 @@ export async function acpSendMessage(
     ? { truncate_before_message_id: truncateBeforeMessageId }
     : undefined;
 
-  const messageId = crypto.randomUUID();
+  const messageId = options.messageId ?? crypto.randomUUID();
   setActiveMessageId(gooseSessionId, messageId);
 
   await directAcp.prompt(gooseSessionId, content, messageId, meta);