🤖 fix: use ResultSchema for sendMessage output to prevent field stripping (#773)

## Summary
- Fix workspace creation failing with "Unexpected response from server"
due to Zod schema union ordering
- `z.union()` was matching `ResultSchema(z.void())` first, which
stripped `workspaceId`/`metadata` as "extra keys"
- Replaced with single `ResultSchema` using optional fields for
consistent response shape

## Test plan
- [x] `make typecheck` passes
- [x] `useCreationWorkspace.test.tsx` tests pass
- [x] Manual test: create new workspace from scratch - should navigate
to workspace instead of showing error toast

_Generated with `mux`_

Signed-off-by: Thomas Kosiewski <[email protected]>

Author: ThomasK33

src/browser/components/ChatInput/useCreationWorkspace.test.tsx

@@ -138,14 +138,16 @@ const setupWindow = ({ listBranches, sendMessage }: SetupWindowOptions = {}) =>
       if (!args.workspaceId) {
         return Promise.resolve({
           success: true,
-          workspaceId: TEST_WORKSPACE_ID,
-          metadata: TEST_METADATA,
+          data: {
+            workspaceId: TEST_WORKSPACE_ID,
+            metadata: TEST_METADATA,
+          },
         } satisfies WorkspaceSendMessageResult);
       }
 
       const existingWorkspaceResult: WorkspaceSendMessageResult = {
         success: true,
-        data: undefined,
+        data: {},
       };
       return Promise.resolve(existingWorkspaceResult);
     });
@@ -357,8 +359,10 @@ describe("useCreationWorkspace", () => {
       (_args: WorkspaceSendMessageArgs): Promise<WorkspaceSendMessageResult> =>
         Promise.resolve({
           success: true as const,
-          workspaceId: TEST_WORKSPACE_ID,
-          metadata: TEST_METADATA,
+          data: {
+            workspaceId: TEST_WORKSPACE_ID,
+            metadata: TEST_METADATA,
+          },
         })
     );
     const { workspaceApi } = setupWindow({

src/browser/components/ChatInput/useCreationWorkspace.ts

@@ -128,16 +128,17 @@ export function useCreationWorkspace({
           return false;
         }
 
-        // Check if this is a workspace creation result (has metadata field)
-        if ("metadata" in result && result.metadata) {
-          syncCreationPreferences(projectPath, result.metadata.id);
+        // Check if this is a workspace creation result (has metadata in data)
+        const { metadata } = result.data;
+        if (metadata) {
+          syncCreationPreferences(projectPath, metadata.id);
           if (projectPath) {
             const pendingInputKey = getInputKey(getPendingScopeId(projectPath));
             updatePersistedState(pendingInputKey, "");
           }
           // Settings are already persisted via useDraftWorkspaceSettings
           // Notify parent to switch workspace (clears input via parent unmount)
-          onWorkspaceCreated(result.metadata);
+          onWorkspaceCreated(metadata);
           setIsSending(false);
           return true;
         } else {

src/common/orpc/schemas/api.ts

@@ -167,14 +167,13 @@ export const workspace = {
         trunkBranch: z.string().optional(),
       }).optional(),
     }),
-    output: z.union([
-      ResultSchema(z.void(), SendMessageErrorSchema),
+    output: ResultSchema(
       z.object({
-        success: z.literal(true),
-        workspaceId: z.string(),
-        metadata: FrontendWorkspaceMetadataSchema,
+        workspaceId: z.string().optional(),
+        metadata: FrontendWorkspaceMetadataSchema.optional(),
       }),
-    ]),
+      SendMessageErrorSchema
+    ),
   },
   resumeStream: {
     input: z.object({

src/node/orpc/router.ts

@@ -199,35 +199,30 @@ export const router = (authToken?: string) => {
           const result = await context.workspaceService.sendMessage(
             input.workspaceId,
             input.message,
-            input.options // Cast to avoid Zod vs Interface mismatch
+            input.options
           );
 
-          // Type mismatch handling: WorkspaceService returns Result<any>.
-          // Our schema output is ResultSchema(void, SendMessageError) OR {success:true, ...}
-          // We need to ensure strict type alignment.
           if (!result.success) {
             const error =
               typeof result.error === "string"
                 ? { type: "unknown" as const, raw: result.error }
                 : result.error;
             return { success: false, error };
           }
-          // If success, it returns different shapes depending on lazy creation.
-          // If lazy creation happened, it returns {success: true, workspaceId, metadata}
-          // If regular message, it returns {success: true, data: ...} -> wait, result.data is undefined for normal message?
-          // SendMessage in AgentSession returns Result<void> mostly.
-          // But createForFirstMessage returns object.
 
-          // Check result shape
+          // Check if this is a workspace creation result
           if ("workspaceId" in result) {
             return {
               success: true,
-              workspaceId: result.workspaceId,
-              metadata: result.metadata,
+              data: {
+                workspaceId: result.workspaceId,
+                metadata: result.metadata,
+              },
             };
           }
 
-          return { success: true, data: undefined };
+          // Regular message send (no workspace creation)
+          return { success: true, data: {} };
         }),
       resumeStream: t
         .input(schemas.workspace.resumeStream.input)

src/node/services/workspaceService.ts

@@ -453,6 +453,7 @@ export class WorkspaceService extends EventEmitter {
 
       const allMetadata = await this.config.getAllWorkspaceMetadata();
       const completeMetadata = allMetadata.find((m) => m.id === workspaceId);
+
       if (!completeMetadata) {
         return { success: false, error: "Failed to retrieve workspace metadata" };
       }

tests/integration/helpers.ts

@@ -132,12 +132,12 @@ export async function sendMessage(
     return { success: false, error: { type: "unknown", raw } };
   }
 
-  if (result.success && "workspaceId" in result) {
-    // Lazy workspace creation path returns metadata/workspaceId; normalize to void success for callers
+  // Normalize to Result<void> for callers - they just care about success/failure
+  if (result.success) {
     return { success: true, data: undefined };
   }
 
-  return result;
+  return { success: false, error: result.error };
 }
 
 /**