Fix draft agent handoff continuity

Move optimistic user message reconciliation into the stream reducers and keep draft-created agents in a handoff lifecycle until authoritative history lands.

packages/app/src/screens/workspace/workspace-pane-content.test.tsx

@@ -48,14 +48,14 @@ function ProbePanel() {
   return null;
 }
 
-const tab: WorkspaceTabDescriptor = {
+const agentTab: WorkspaceTabDescriptor = {
   key: "agent_agent-a",
   tabId: "agent_agent-a",
   kind: "agent",
   target: { kind: "agent", agentId: "agent-a" },
 };
 
-function buildContent() {
+function buildContent(tab: WorkspaceTabDescriptor = agentTab) {
   return buildWorkspacePaneContentModel({
     tab,
     normalizedServerId: "server-a",
@@ -120,4 +120,43 @@ describe("WorkspacePaneContent", () => {
       focusPane: expect.any(Function),
     });
   });
+
+  it("keeps pane content mounted when a draft tab is retargeted in place", () => {
+    container = document.createElement("div");
+    document.body.appendChild(container);
+    root = createRoot(container);
+
+    const draftContent = buildContent({
+      key: "draft-a",
+      tabId: "draft-a",
+      kind: "draft",
+      target: { kind: "draft", draftId: "draft-a" },
+    });
+    const agentContent = buildContent({
+      key: "draft-a",
+      tabId: "draft-a",
+      kind: "agent",
+      target: { kind: "agent", agentId: "agent-a" },
+    });
+
+    act(() => {
+      root?.render(
+        <WorkspacePaneContent content={draftContent} isPaneFocused isWorkspaceFocused={true} />,
+      );
+    });
+    act(() => {
+      root?.render(
+        <WorkspacePaneContent content={agentContent} isPaneFocused isWorkspaceFocused={true} />,
+      );
+    });
+
+    expect(mountCount).toHaveBeenCalledTimes(1);
+    expect(unmountCount).not.toHaveBeenCalled();
+    expect(snapshots).toHaveLength(2);
+    expect(snapshots[1]?.paneContextValue.tabId).toBe("draft-a");
+    expect(snapshots[1]?.paneContextValue.target).toEqual({
+      kind: "agent",
+      agentId: "agent-a",
+    });
+  });
 });

packages/app/src/screens/workspace/workspace-pane-content.tsx

@@ -42,7 +42,7 @@ export function buildWorkspacePaneContentModel({
   const registration = getPanelRegistration(tab.kind);
   invariant(registration, `No panel registration for kind: ${tab.kind}`);
   return {
-    key: `${normalizedServerId}:${normalizedWorkspaceId}:${tab.tabId}:${tab.kind}`,
+    key: `${normalizedServerId}:${normalizedWorkspaceId}:${tab.tabId}`,
     Component: registration.component,
     paneContextValue: {
       serverId: normalizedServerId,

packages/app/src/screens/workspace/workspace-screen.tsx

@@ -1746,9 +1746,6 @@ function WorkspaceScreenContent({
   const unpinWorkspaceAgent = useWorkspaceLayoutStore((state) => state.unpinAgent);
   const hideWorkspaceAgent = useWorkspaceLayoutStore((state) => state.hideAgent);
   const retargetWorkspaceTab = useWorkspaceLayoutStore((state) => state.retargetTab);
-  const convertWorkspaceDraftToAgent = useWorkspaceLayoutStore(
-    (state) => state.convertDraftToAgent,
-  );
   const reconcileWorkspaceTabs = useWorkspaceLayoutStore((state) => state.reconcileTabs);
   const splitWorkspacePane = useWorkspaceLayoutStore((state) => state.splitPane);
   const splitWorkspacePaneEmpty = useWorkspaceLayoutStore((state) => state.splitPaneEmpty);
@@ -2842,10 +2839,6 @@ function WorkspaceScreenContent({
           if (!persistenceKey) {
             return;
           }
-          if (input.tab.kind === "draft" && target.kind === "agent") {
-            convertWorkspaceDraftToAgent(persistenceKey, input.tab.tabId, target.agentId);
-            return;
-          }
           retargetWorkspaceTab(persistenceKey, input.tab.tabId, target);
         },
         onOpenWorkspaceFile: (request: WorkspaceFileOpenRequest) => {
@@ -2875,7 +2868,6 @@ function WorkspaceScreenContent({
       openImportSheet,
       openWorkspaceChildTabFocused,
       persistenceKey,
-      convertWorkspaceDraftToAgent,
       retargetWorkspaceTab,
     ],
   );