feat: open Changes as a workspace tab (#2298)

Open the complete working comparison in a desktop workspace tab while preserving inline sidebar diffs when the tab is closed.

Working and commit comparisons share one diff panel, and workspace layout is the sole owner of live tab persistence and identity.

Refs #1520

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

@@ -44,6 +44,42 @@ describe("provider subagent tab identity", () => {
   });
 });
 
+describe("working diff tab identity", () => {
+  const target = {
+    kind: "working_diff" as const,
+    focusPath: "src/example.ts",
+    focusRequestId: 1,
+  };
+
+  it("normalizes file focus navigation", () => {
+    expect(
+      normalizeWorkspaceTabTarget({
+        ...target,
+        focusPath: " src\\example.ts ",
+      }),
+    ).toEqual(target);
+  });
+
+  it("treats focus as navigation state rather than tab identity", () => {
+    expect(workspaceTabTargetsEqual(target, target)).toBe(true);
+    expect(workspaceTabTargetsEqual(target, { ...target, focusPath: "src/other.ts" })).toBe(false);
+    expect(workspaceTabTargetsEqual(target, { ...target, focusRequestId: 2 })).toBe(false);
+    const workingDiffId = buildDeterministicWorkspaceTabId(target);
+    const otherFocusId = buildDeterministicWorkspaceTabId({
+      ...target,
+      focusPath: "src/other.ts",
+    });
+    const fileId = buildDeterministicWorkspaceTabId({
+      kind: "file",
+      path: target.focusPath,
+    });
+
+    expect(workingDiffId).toBe("working_diff");
+    expect(workingDiffId).toBe(otherFocusId);
+    expect(workingDiffId).not.toBe(fileId);
+  });
+});
+
 describe("commit diff tab identity", () => {
   it("keys a commit diff tab by its sha", () => {
     expect(buildDeterministicWorkspaceTabId({ kind: "commit_diff", sha: "abc123" })).toBe(