Make the workspace right pane a first-class tab host (#3287)

* feat(app): add persistent workspace side panes

Keep the common review and file-browsing workflow beside the active agent without tearing down pane contents. Workspace tabs now share one compact chip language, assistant file links route into the retained right pane, and diff/file trees share stable geometry.

* fix(app): localize pull request empty state

* test(app): update explorer pane coverage

* fix(app): preserve explorer pane workflows

* test(app): make explorer tab selection idempotent

* fix(app): persist workspace review pins

* fix(app): preserve sidebar scrim drag hook

* fix(app): restore companion pane interactions

* test(app): follow selected sidebar surface

packages/app/src/composer/focused-chat-target.test.ts

@@ -46,4 +46,32 @@ describe("focused chat target", () => {
       }),
     ).toBeNull();
   });
+
+  it("targets a utility tab's parent chat", () => {
+    const layout = {
+      root: {
+        kind: "pane",
+        pane: {
+          id: "pane-1",
+          tabIds: ["agent-tab", "changes-tab"],
+          focusedTabId: "changes-tab",
+          tabs: [
+            {
+              tabId: "agent-tab",
+              target: { kind: "agent", agentId: "agent-1" },
+              createdAt: 1,
+            },
+            { tabId: "changes-tab", target: { kind: "working_diff" }, createdAt: 2 },
+          ],
+        },
+      },
+      focusedPaneId: "pane-1",
+      parentTabIdByTabId: { "changes-tab": "agent-tab" },
+    } as WorkspaceLayout;
+
+    expect(resolveFocusedChatTarget({ serverId: "server-1", layout })).toEqual({
+      tabId: "agent-tab",
+      draftKey: "agent:server-1:agent-1",
+    });
+  });
 });

packages/app/src/composer/focused-chat-target.ts

@@ -10,6 +10,29 @@ export interface FocusedChatTarget {
   draftKey: string;
 }
 
+function resolveChatTab(
+  serverId: string,
+  tab: ReturnType<typeof collectAllTabs>[number] | undefined,
+): FocusedChatTarget | null {
+  if (tab?.target.kind === "agent") {
+    return {
+      tabId: tab.tabId,
+      draftKey: buildDraftStoreKey({ serverId, agentId: tab.target.agentId }),
+    };
+  }
+  if (tab?.target.kind === "draft") {
+    return {
+      tabId: tab.tabId,
+      draftKey: buildDraftStoreKey({
+        serverId,
+        agentId: tab.tabId,
+        draftId: tab.target.draftId,
+      }),
+    };
+  }
+  return null;
+}
+
 export function resolveFocusedChatTarget(input: {
   serverId: string;
   layout: WorkspaceLayout | undefined;
@@ -22,27 +45,15 @@ export function resolveFocusedChatTarget(input: {
   if (!focusedTabId) {
     return null;
   }
-  const tab = collectAllTabs(input.layout.root).find(
-    (candidate) => candidate.tabId === focusedTabId,
+  const tabs = collectAllTabs(input.layout.root);
+  const tab = tabs.find((candidate) => candidate.tabId === focusedTabId);
+  const focusedChat = resolveChatTab(input.serverId, tab);
+  if (focusedChat) {
+    return focusedChat;
+  }
+  const parentTabId = input.layout.parentTabIdByTabId?.[focusedTabId];
+  return resolveChatTab(
+    input.serverId,
+    tabs.find((candidate) => candidate.tabId === parentTabId),
   );
-  if (!tab) {
-    return null;
-  }
-  if (tab.target.kind === "agent") {
-    return {
-      tabId: tab.tabId,
-      draftKey: buildDraftStoreKey({ serverId: input.serverId, agentId: tab.target.agentId }),
-    };
-  }
-  if (tab.target.kind === "draft") {
-    return {
-      tabId: tab.tabId,
-      draftKey: buildDraftStoreKey({
-        serverId: input.serverId,
-        agentId: tab.tabId,
-        draftId: tab.target.draftId,
-      }),
-    };
-  }
-  return null;
 }