fix(tools): join char-split JSON arrays from local LLMs

Some models emit tool array args as one string per character (e.g. UpdateTodoList
tasks). Rejoin and parse before normalize_task_items / ReadRange show ops.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: JessicaMulein

cecli/tools/utils/helpers.py

@@ -346,12 +346,46 @@ def format_tool_result(
         return result_for_llm
 
 
+def _try_join_char_split_json_array(items: list) -> list | None:
+    """
+    Some local models emit a JSON array as one string per character in tool args.
+
+    Example: tasks=["[", "{", "\\"", "t", "a", "s", "k", "\\"", ...] instead of
+    tasks='[{"task": "...", "done": false}]'.
+    """
+    if len(items) < 8:
+        return None
+    if not all(isinstance(x, str) for x in items):
+        return None
+    joined = "".join(items).strip()
+    if not joined.startswith(("[", "{")):
+        return None
+    try:
+        parsed = json.loads(joined)
+    except json.JSONDecodeError:
+        return None
+    if isinstance(parsed, dict):
+        return [parsed]
+    if isinstance(parsed, list):
+        return parsed
+    return None
+
+
 def normalize_json_array(value, *, param_name: str = "items", allow_empty: bool = False) -> list:
     """
     Coerce tool args that should be arrays but sometimes arrive as JSON strings.
 
-    Local models occasionally double-encode array parameters as JSON text.
+    Local models occasionally double-encode array parameters as JSON text, or emit
+    arrays as per-character string lists (see ``_try_join_char_split_json_array``).
     """
+    if isinstance(value, list):
+        coerced = _try_join_char_split_json_array(value)
+        if coerced is not None:
+            value = coerced
+        elif len(value) == 1 and isinstance(value[0], str):
+            # Single element wrapping the whole JSON array/object as a string.
+            value = value[0]
+
     if isinstance(value, str):
         text = value.strip()
         if not text:

tests/tools/test_get_lines.py

@@ -184,3 +184,13 @@ def test_format_output_accepts_show_as_json_string(coder_with_file):
     assert "example.txt" in output_text
     assert "alpha" in output_text
     coder.io.tool_error.assert_not_called()
+
+
+def test_normalize_show_ops_joins_char_split_json_list():
+    show_json = json.dumps(
+        [{"file_path": "docs/ROADMAP.md", "start_text": "@000", "end_text": "\\n"}]
+    )
+    ops = normalize_show_ops(list(show_json))
+    assert len(ops) == 1
+    assert ops[0]["file_path"] == "docs/ROADMAP.md"
+    assert ops[0]["start_text"] == "@000"

tests/tools/test_update_todo_list.py

@@ -50,6 +50,35 @@ def test_normalize_task_items_accepts_list_of_json_strings():
     assert items[1]["task"] == "Second"
 
 
+def test_normalize_json_array_joins_char_split_json_list():
+    """Ollama sometimes sends tasks as a list of single-character strings."""
+    chars = list(
+        '[{"task": "Explore the codebase", "done": false, "current": true},'
+        '{"task": "Draft roadmap", "done": false}]'
+    )
+    items = normalize_json_array(chars, param_name="tasks")
+    assert len(items) == 2
+    assert items[0]["task"] == "Explore the codebase"
+    assert items[1]["task"] == "Draft roadmap"
+
+
+def test_normalize_json_array_unwraps_single_element_json_string_list():
+    wrapped = [
+        '[{"task": "Only task", "done": false}]',
+    ]
+    items = normalize_json_array(wrapped, param_name="tasks")
+    assert len(items) == 1
+    assert items[0]["task"] == "Only task"
+
+
+def test_normalize_task_items_from_char_split_list():
+    chars = list(json.dumps([{"task": "Ship tests", "done": True}]))
+    items = normalize_task_items(chars)
+    assert len(items) == 1
+    assert items[0]["task"] == "Ship tests"
+    assert items[0]["done"] is True
+
+
 def test_normalize_task_items_does_not_split_characters():
     tasks_json = json.dumps([{"task": "Only one task", "done": False}])
     items = normalize_task_items(tasks_json)
@@ -103,6 +132,32 @@ def test_format_output_accepts_tasks_as_json_string():
     coder.io.tool_error.assert_not_called()
 
 
+def test_format_output_accepts_char_split_tasks_list():
+    """Reproduces BrightVision bug: tasks array is one JSON character per element."""
+    coder = DummyCoder()
+    tasks_json = (
+        '[{"task": "Explore the codebase", "done": false, "current": true},'
+        '{"task": "Draft roadmap items", "done": false}]'
+    )
+    args = json.dumps({"tasks": list(tasks_json)})
+    tool_response = SimpleNamespace(function=SimpleNamespace(name="UpdateTodoList", arguments=args))
+
+    update_todo_list.Tool.format_output(
+        coder,
+        mcp_server=SimpleNamespace(name="test"),
+        tool_response=tool_response,
+    )
+
+    output_text = "\n".join(call.args[0] for call in coder.io.tool_output.call_args_list)
+    assert "Explore the codebase" in output_text
+    assert "Draft roadmap items" in output_text
+    assert output_text.count("○ ") == 1
+    assert "→ Explore the codebase" in output_text
+    assert "○ Draft roadmap items" in output_text
+    assert all(len(line.strip()) > 3 for line in output_text.splitlines() if line.startswith("○ "))
+    coder.io.tool_error.assert_not_called()
+
+
 def test_format_output_reports_invalid_tool_arguments_json():
     coder = DummyCoder()
     tool_response = SimpleNamespace(