feat(cli): show todo progress as done/total fraction

Parse the todo_tool result summary to display completion progress in
CLI tool preview lines:

  Read:    ┊ 📋 plan      3/4 task(s)  0.5s
  Update:  ┊ 📋 plan      update 3/4 ✓  0.5s
  Create:  falls back to plain count when no completed tasks

Falls back gracefully to the existing 'N task(s)' format when the
result is missing, malformed, or has no completed items.

Originally proposed in PR #17194 by Albert.Zhou; salvaged onto current
main.

Co-authored-by: Albert.Zhou <albert748@gmail.com>

tests/agent/test_display_todo_progress.py

@@ -0,0 +1,243 @@
+"""Tests for get_cute_tool_message todo progress display.
+
+Verifies the completion status rendering (done/total ✓) on all three
+todo tool call paths: read, create (merge=False), update (merge=True).
+"""
+
+import json
+import pytest
+from agent.display import get_cute_tool_message
+
+
+def _todo_result(total: int, completed: int) -> str:
+    """Build a fake todo_tool return value."""
+    return json.dumps({
+        "todos": [],
+        "summary": {
+            "total": total,
+            "pending": total - completed,
+            "in_progress": 0,
+            "completed": completed,
+            "cancelled": 0,
+        },
+    })
+
+
+class TestTodoRead:
+    """get_cute_tool_message(…, result=…) when todos_arg is None (read path)."""
+
+    def test_read_no_result(self):
+        msg = get_cute_tool_message("todo", {}, 0.5)
+        assert "reading tasks" in msg
+        assert "0.5s" in msg
+
+    def test_read_with_progress(self):
+        msg = get_cute_tool_message("todo", {}, 0.5,
+                                    result=_todo_result(4, 2))
+        assert "2/4" in msg
+        assert "task(s)" in msg
+
+    def test_read_all_done(self):
+        msg = get_cute_tool_message("todo", {}, 0.5,
+                                    result=_todo_result(4, 4))
+        assert "4/4" in msg
+        assert "task(s)" in msg
+
+    def test_read_zero_total(self):
+        """Edge case: empty todo list returns summary with total=0."""
+        msg = get_cute_tool_message("todo", {}, 0.5,
+                                    result=_todo_result(0, 0))
+        assert "reading tasks" in msg
+
+    def test_read_invalid_result_fallback(self):
+        """Garbage result should not crash; fall back to reading tasks."""
+        msg = get_cute_tool_message("todo", {}, 0.5, result="not json")
+        assert "reading tasks" in msg
+
+    def test_read_result_missing_summary(self):
+        msg = get_cute_tool_message("todo", {}, 0.5,
+                                    result='{"todos": []}')
+        assert "reading tasks" in msg
+
+
+class TestTodoCreate:
+    """get_cute_tool_message when merge=False (new plan creation)."""
+
+    def test_create_default(self):
+        """Brand-new plan: all pending, no result — plain count."""
+        msg = get_cute_tool_message("todo",
+                                    {"todos": [
+                                        {"id": "a", "content": "x", "status": "pending"},
+                                    ]}, 0.3)
+        assert "1 task(s)" in msg
+        assert "0.3s" in msg
+        assert "/" not in msg  # no progress fraction
+
+    def test_create_multiple(self):
+        msg = get_cute_tool_message("todo",
+                                    {"todos": [
+                                        {"id": "a", "content": "x", "status": "pending"},
+                                        {"id": "b", "content": "y", "status": "pending"},
+                                        {"id": "c", "content": "z", "status": "pending"},
+                                    ]}, 0.2)
+        assert "3 task(s)" in msg
+
+    def test_create_with_result_shows_progress_when_done(self):
+        """Even on create, if result has completed tasks show it."""
+        msg = get_cute_tool_message("todo",
+                                    {"todos": [{"id": "a", "content": "x", "status": "completed"}]},
+                                    0.4,
+                                    result=_todo_result(1, 1))
+        assert "1/1" in msg
+        assert "task(s)" in msg
+
+    def test_create_with_result_zero_done(self):
+        """New plan with 0 done — plain count, no progress fraction."""
+        msg = get_cute_tool_message("todo",
+                                    {"todos": [
+                                        {"id": "a", "content": "x", "status": "pending"},
+                                        {"id": "b", "content": "y", "status": "pending"},
+                                    ]},
+                                    0.3,
+                                    result=_todo_result(2, 0))
+        assert "2 task(s)" in msg
+        assert "/" not in msg
+
+
+class TestTodoUpdate:
+    """get_cute_tool_message when merge=True (incremental update)."""
+
+    def test_update_no_result(self):
+        """No result available — plain update N task(s)."""
+        msg = get_cute_tool_message("todo",
+                                    {"todos": [{"id": "a", "status": "completed"}],
+                                     "merge": True}, 0.5)
+        assert "update 1 task(s)" in msg
+
+    def test_update_partial_progress(self):
+        """1/4 tasks completed — show fraction with checkmark."""
+        msg = get_cute_tool_message("todo",
+                                    {"todos": [{"id": "a", "status": "completed"}],
+                                     "merge": True},
+                                    0.5,
+                                    result=_todo_result(4, 1))
+        assert "update" in msg
+        assert "1/4" in msg
+        assert "✓" in msg
+
+    def test_update_halfway(self):
+        """2/4 — midpoint progress."""
+        msg = get_cute_tool_message("todo",
+                                    {"todos": [{"id": "b", "status": "in_progress"}],
+                                     "merge": True},
+                                    0.7,
+                                    result=_todo_result(4, 2))
+        assert "2/4" in msg
+        assert "✓" in msg
+
+    def test_update_all_completed(self):
+        """4/4 — full checkmark."""
+        msg = get_cute_tool_message("todo",
+                                    {"todos": [{"id": "d", "status": "completed"}],
+                                     "merge": True},
+                                    0.2,
+                                    result=_todo_result(4, 4))
+        assert "4/4" in msg
+        assert "✓" in msg
+
+    def test_update_zero_done(self):
+        """No completed tasks yet — plain update N task(s)."""
+        msg = get_cute_tool_message("todo",
+                                    {"todos": [{"id": "a", "status": "pending"}],
+                                     "merge": True},
+                                    0.3,
+                                    result=_todo_result(3, 0))
+        assert "update 1 task(s)" in msg
+        assert "✓" not in msg
+        assert "/" not in msg  # no progress fraction when done=0
+
+    def test_update_invalid_result_fallback(self):
+        """Bad JSON result — fall back to plain update N task(s)."""
+        msg = get_cute_tool_message("todo",
+                                    {"todos": [{"id": "a", "status": "completed"}],
+                                     "merge": True},
+                                    0.6,
+                                    result="{broken")
+        assert "update 1 task(s)" in msg
+        assert "✓" not in msg
+
+    def test_update_result_missing_summary(self):
+        """Result no summary key — fall back to plain update."""
+        msg = get_cute_tool_message("todo",
+                                    {"todos": [{"id": "a", "status": "completed"}],
+                                     "merge": True},
+                                    0.4,
+                                    result='{"todos": []}')
+        assert "update 1 task(s)" in msg
+        assert "✓" not in msg
+
+    def test_update_total_not_in_summary(self):
+        """Result summary missing total key."""
+        msg = get_cute_tool_message("todo",
+                                    {"todos": [{"id": "a", "status": "completed"}],
+                                     "merge": True},
+                                    0.3,
+                                    result=json.dumps({"summary": {"completed": 2}}))
+        assert "update 1 task(s)" in msg
+        assert "✓" not in msg
+
+    def test_update_multiple_tasks_in_line(self):
+        """Update line with several tasks in the update request."""
+        msg = get_cute_tool_message("todo",
+                                    {"todos": [
+                                        {"id": "a", "status": "completed"},
+                                        {"id": "b", "status": "in_progress"},
+                                    ], "merge": True},
+                                    0.5,
+                                    result=_todo_result(5, 3))
+        assert "update" in msg
+        assert "3/5" in msg
+        assert "✓" in msg
+
+
+class TestTodoEdgeCases:
+    """Boundary cases that should not crash."""
+
+    def test_merge_default_value(self):
+        """merge defaults to False in function signature, should be False when absent."""
+        msg = get_cute_tool_message("todo",
+                                    {"todos": [{"id": "a", "content": "x", "status": "pending"}]},
+                                    1.0)
+        assert "1 task(s)" in msg
+
+    def test_duration_formatting(self):
+        """Duration formatting works correctly."""
+        msg = get_cute_tool_message("todo", {}, 0.123)
+        assert "0.1s" in msg
+
+        msg = get_cute_tool_message("todo", {}, 1.0)
+        assert "1.0s" in msg
+
+        msg = get_cute_tool_message("todo", {}, 123.456)
+        assert "123.5s" in msg
+
+    def test_large_task_count(self):
+        """Many tasks should not break formatting."""
+        many = [{"id": str(i), "content": "x", "status": "pending"} for i in range(50)]
+        msg = get_cute_tool_message("todo", {"todos": many}, 0.5)
+        assert "50 task(s)" in msg
+
+    def test_read_with_no_args_and_no_result(self):
+        """Completely empty call."""
+        msg = get_cute_tool_message("todo", {}, 0.0)
+        assert "reading tasks" in msg
+
+
+class TestTodoSkinIntegration:
+    """Verify the skin prefix is applied to todo messages too.
+    This uses the same pattern as test_skin_engine test_tool_message_uses_skin_prefix.
+    """
+
+    def test_default_skin_prefix(self):
+        msg = get_cute_tool_message("todo", {}, 0.5)
+        assert msg.startswith("┊")