cli/display: merge a batch of todo calls into one line

A round that updated its todo list printed one header plus a full stack
render per call, so the same list appeared several times. When a batch only
touches todo tools, print one `* Todo x<N>: Push, Update` line and the last
result, whose text already ends with the final stack. A batch holding any
other tool keeps the per-call lines, and a todo call never prints a prefix
at call time (it would dangle when the batch is merged).

tests/test_cli/test_display.py

@@ -186,6 +186,51 @@ async def test_pretty_todo_push(capsys: pytest.CaptureFixture[str]) -> None:
     assert "[tool]" not in out
 
 
+async def test_pretty_todo_batch_merges_to_one_stack(capsys: pytest.CaptureFixture[str]) -> None:
+    """A batch of todo calls: one summary line, then the last result's stack."""
+    stack = "(LIFO of groups: depth=1; TOP group = current breakdown level)\ngroup d=0 TOP:\n  [ ] a1: T1"
+    await render_events(
+        _aiter(
+            [
+                _pretty_call("todo_push", '{"titles": ["T1"]}'),
+                _pretty_call("todo_update", '{"item_id": "a1", "status": "done"}'),
+                _result(f"pushed group (depth=1) items=[a1]\n{stack}"),
+                _result(f"updated a1 → done: T1\n{stack}"),
+            ]
+        )
+    )
+    out = capsys.readouterr().out
+    assert "* Todo x2: Push, Update" in out
+    assert "* Todo Push:" not in out
+    assert "* Todo Update:" not in out
+    # Only the last result is printed, so the stack renders once.
+    assert out.count("group d=0 TOP:") == 1
+    assert "pushed group" not in out
+    assert "updated a1 → done: T1" in out
+
+
+async def test_pretty_todo_batch_mixed_with_other_tool_stays_per_call(
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    """A batch holding a non-todo call keeps one line (and stack) per todo call."""
+    stack = "group d=0 TOP:\n  [ ] a1: T1"
+    await render_events(
+        _aiter(
+            [
+                _pretty_call("todo_push", '{"titles": ["T1"]}'),
+                _pretty_call("listdir", '{"path": "src"}'),
+                _result(f"pushed group (depth=1) items=[a1]\n{stack}"),
+                _result("dir\tsrc\nfile\tREADME.md\n"),
+            ]
+        )
+    )
+    out = capsys.readouterr().out
+    assert "* Todo Push:" in out
+    assert "group d=0 TOP:" in out
+    assert "src" in out
+    assert "* Todo x" not in out
+
+
 async def test_non_pretty_tool_keeps_old_style(capsys: pytest.CaptureFixture[str]) -> None:
     """Tools with no pretty line (plugins, unknown names) keep the ``[tool]`` style."""
     call = ToolCallEvent(