Collapse completed todo subtrees in widget

tests/ui.test.ts

@@ -9,6 +9,7 @@ import {
   renderTaskLine,
   renderToolResult,
   renderTree,
+  renderWidgetTree,
   snapshotStats,
 } from "../src/ui.ts";
 import { updateTaskWidget } from "../src/widget.ts";
@@ -67,6 +68,56 @@ test("renders lightweight connectors without a detached root continuation", () =
   ]);
 });
 
+test("collapses completed widget subtrees while keeping list trees expanded", () => {
+  const state = new TaskState(() => 0);
+  state.add([
+    {
+      name: "Release",
+      children: [
+        {
+          name: "Completed branch",
+          children: [
+            { name: "Done one", status: "done" },
+            { name: "Done two", status: "done" },
+          ],
+        },
+        { name: "Open branch", children: [{ name: "Open leaf" }] },
+      ],
+    },
+    {
+      name: "Pending parent",
+      children: [{ name: "Finished child", status: "done" }],
+    },
+  ]);
+
+  const widgetLines = renderWidgetTree(state.list(), plainTheme as never, 80).map(stripAnsi);
+  assert.deepEqual(widgetLines, [
+    "  ○ 1. Release",
+    "  ├─ ○ 2. Completed branch · 2/2 done",
+    "  └─ ○ 5. Open branch",
+    "     └─ ○ 6. Open leaf",
+    "  ○ 7. Pending parent · 1/1 done",
+  ]);
+
+  const fullTree = renderTree(state.list(), plainTheme as never, 80).map(stripAnsi);
+  assert.ok(fullTree.some((line) => line.includes("Done one")));
+  assert.ok(fullTree.some((line) => line.includes("Finished child")));
+
+  state.update([{ id: 3, status: "pending" }]);
+  const reopened = renderWidgetTree(state.list(), plainTheme as never, 80).map(stripAnsi);
+  assert.ok(reopened.some((line) => line.includes("Done one")));
+  assert.ok(reopened.some((line) => line.includes("Done two")));
+});
+
+test("hides a completed widget summary before squeezing the task name", () => {
+  const state = new TaskState(() => 0);
+  state.add([{ name: "A long parent task name", children: [{ name: "Done", status: "done" }] }]);
+
+  const line = renderWidgetTree(state.list(), plainTheme as never, 20)[0] ?? "";
+  assert.ok(visibleWidth(line) <= 20);
+  assert.doesNotMatch(stripAnsi(line), /done$/);
+});
+
 test("formats compact timers and adds hours only when needed", () => {
   assert.equal(formatDuration(0), "00:00");
   assert.equal(formatDuration(65_432), "01:05");