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/workspace-tabs/identity.test.ts

@@ -80,6 +80,19 @@ describe("working diff tab identity", () => {
   });
 });
 
+describe("workspace utility panel identity", () => {
+  it.each(["files", "pull_request"] as const)(
+    "normalizes and deterministically keys %s",
+    (kind) => {
+      const target = { kind };
+
+      expect(normalizeWorkspaceTabTarget(target)).toEqual(target);
+      expect(buildDeterministicWorkspaceTabId(target)).toBe(kind);
+      expect(workspaceTabTargetsEqual(target, target)).toBe(true);
+    },
+  );
+});
+
 describe("commit diff tab identity", () => {
   it("keys a commit diff tab by its sha", () => {
     expect(buildDeterministicWorkspaceTabId({ kind: "commit_diff", sha: "abc123" })).toBe(

packages/app/src/workspace-tabs/identity.ts

@@ -49,6 +49,9 @@ function normalizeSimpleWorkspaceTabTarget(value: WorkspaceTabTarget): Workspace
       const browserId = trimNonEmpty(value.browserId);
       return browserId ? { kind: "browser", browserId } : null;
     }
+    case "files":
+    case "pull_request":
+      return { kind: value.kind };
     case "setup": {
       const workspaceId = trimNonEmpty(value.workspaceId);
       return workspaceId ? { kind: "setup", workspaceId } : null;
@@ -121,6 +124,12 @@ function secondaryWorkspaceTabTargetsEqual(
   if (left.kind === "working_diff" && right.kind === "working_diff") {
     return left.focusPath === right.focusPath && left.focusRequestId === right.focusRequestId;
   }
+  if (left.kind === "files" && right.kind === "files") {
+    return true;
+  }
+  if (left.kind === "pull_request" && right.kind === "pull_request") {
+    return true;
+  }
   if (left.kind === "setup" && right.kind === "setup") {
     return left.workspaceId === right.workspaceId;
   }
@@ -188,6 +197,9 @@ export function buildDeterministicWorkspaceTabId(target: WorkspaceTabTarget): st
   if (target.kind === "working_diff") {
     return "working_diff";
   }
+  if (target.kind === "files" || target.kind === "pull_request") {
+    return target.kind;
+  }
   return `file_${target.path}`;
 }
 

packages/app/src/workspace-tabs/model.ts

@@ -22,6 +22,8 @@ export type WorkspaceTabTarget =
   | { kind: "provider_subagent"; parentAgentId: string; subagentId: string }
   | { kind: "terminal"; terminalId: string }
   | { kind: "browser"; browserId: string }
+  | { kind: "files" }
+  | { kind: "pull_request" }
   | WorkspaceFileTabTarget
   | WorkspaceWorkingDiffTabTarget
   | { kind: "setup"; workspaceId: string }