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/utils/split-navigation.test.ts

@@ -2,13 +2,14 @@ import { describe, expect, it } from "vitest";
 import type { SplitNode } from "@/stores/workspace-layout-store";
 import { findAdjacentPane } from "./split-navigation";
 
-function createPaneNode(id: string): SplitNode {
+function createPaneNode(id: string, hidden = false): SplitNode {
   return {
     kind: "pane",
     pane: {
       id,
       tabIds: [],
       focusedTabId: null,
+      ...(hidden ? { hidden: true } : {}),
     },
   };
 }
@@ -80,4 +81,15 @@ describe("findAdjacentPane", () => {
     expect(findAdjacentPane(root, "top", "down")).toBe("bottom-left");
     expect(findAdjacentPane(root, "bottom-right", "up")).toBe("top");
   });
+
+  it("skips hidden panes", () => {
+    const root = createGroupNode({
+      direction: "horizontal",
+      sizes: [0.3, 0.3, 0.4],
+      children: [createPaneNode("left"), createPaneNode("hidden", true), createPaneNode("right")],
+    });
+
+    expect(findAdjacentPane(root, "left", "right")).toBe("right");
+    expect(findAdjacentPane(root, "hidden", "right")).toBeNull();
+  });
 });

packages/app/src/utils/split-navigation.ts

@@ -171,6 +171,9 @@ function collectPaneBounds(
   bounds: { left: number; top: number; right: number; bottom: number },
 ): PaneBounds[] {
   if (node.kind === "pane") {
+    if (node.pane.hidden === true) {
+      return [];
+    }
     return [
       {
         paneId: node.pane.id,