tui: let users review branch changes against main

packages/opencode/test/cli/tui/diff-viewer.test.tsx

@@ -85,6 +85,66 @@ test("closing the diff viewer returns to the route it opened from", async () =>
   }
 })
 
+test("branch diff source requests branch VCS diff", async () => {
+  const calls: Parameters<TuiPluginApi["client"]["vcs"]["diff"]>[0][] = []
+  const current: TuiRouteCurrent = { name: "diff", params: { mode: "branch" } }
+  let renderDiff: TuiRouteDefinition["render"] | undefined
+  await mkdir(Global.Path.state, { recursive: true })
+  await Bun.write(path.join(Global.Path.state, "kv.json"), "{}")
+
+  function Harness() {
+    const renderer = useRenderer()
+    const keymap = createDefaultOpenTuiKeymap(renderer)
+    const base = createTuiPluginApi({
+      keymap,
+      client: {
+        vcs: {
+          diff: async (parameters: Parameters<TuiPluginApi["client"]["vcs"]["diff"]>[0]) => {
+            calls.push(parameters)
+            return { data: [] }
+          },
+        },
+        session: { diff: async () => ({ data: [] }) },
+      } as unknown as TuiPluginApi["client"],
+    })
+    const api = {
+      ...base,
+      route: {
+        register(routes) {
+          renderDiff = routes.find((route) => route.name === "diff")?.render
+          return () => {}
+        },
+        navigate() {},
+        get current() {
+          return current
+        },
+      },
+    } satisfies TuiPluginApi
+
+    void diffViewerPlugin.tui(api, undefined, pluginMeta)
+
+    return (
+      <OpencodeKeymapProvider keymap={keymap}>
+        <TuiConfigProvider config={createTuiResolvedConfig()}>
+          <KVProvider>
+            <ThemeProvider mode="dark">
+              {renderDiff?.({ params: "params" in current ? current.params : undefined })}
+            </ThemeProvider>
+          </KVProvider>
+        </TuiConfigProvider>
+      </OpencodeKeymapProvider>
+    )
+  }
+
+  const app = await testRender(() => <Harness />, { width: 80, height: 20 })
+  try {
+    await waitForCall(app, calls)
+    expect(calls[0]).toEqual({ mode: "branch", context: 12 })
+  } finally {
+    app.renderer.destroy()
+  }
+})
+
 async function waitForCommand(
   app: Awaited<ReturnType<typeof testRender>>,
   commands: Map<string, unknown>,
@@ -97,6 +157,14 @@ async function waitForCommand(
   }
 }
 
+async function waitForCall(app: Awaited<ReturnType<typeof testRender>>, calls: unknown[]) {
+  for (let attempt = 0; attempt < 10; attempt++) {
+    await app.renderOnce()
+    if (calls.length > 0) return
+    await new Promise((resolve) => setTimeout(resolve, 25))
+  }
+}
+
 const pluginMeta = {
   id: "diff-viewer",
   source: "internal",