fix: isolate slash command autocomplete to command names

Author: tunahorse

.claude/debug_history/2026-03-06-command-autocomplete-argument-interference.md

@@ -0,0 +1,33 @@
+---
+title: Slash-command autocomplete intercepted `/skills` argument navigation
+link: command-autocomplete-argument-interference
+type: bugfix
+path: src/tunacode/ui/widgets/command_autocomplete.py
+tags:
+  - ui
+  - autocomplete
+  - commands
+  - skills
+created_at: 2026-03-06T22:35:00-06:00
+updated_at: 2026-03-06T22:35:00-06:00
+---
+
+## Summary
+
+Fixed the root cause of broken `/skills` navigation: the generic slash-command autocomplete was still building candidates while the user was editing command arguments, so arrow and Enter keys could be consumed by the wrong dropdown.
+
+## Trigger
+
+Typing `/skills ...` correctly opened the skills dropdown, but pressing Down caused the hidden slash-command autocomplete to activate and move its own highlight. Enter could then complete `/cancel`, `/compact`, or another slash command instead of the highlighted skill.
+
+## Changes
+
+- Tightened `CommandAutoComplete.get_candidates()` to return candidates only while the user is editing the command-name region before the first space.
+- Reused the same command-name parser already used by visibility logic.
+- Added focused tests proving command autocomplete is inactive during `/skills` argument editing.
+- Added an end-to-end headless UI test proving `/skills ` + Down + Enter selects the highlighted skill, not a slash command.
+
+## Tests
+
+- `uv run pytest tests/unit/ui/test_command_autocomplete.py tests/unit/ui/test_skills_autocomplete.py -q`
+- `uv run ruff check src/tunacode/ui/widgets/command_autocomplete.py tests/unit/ui/test_command_autocomplete.py tests/unit/ui/test_skills_autocomplete.py`

src/tunacode/ui/widgets/command_autocomplete.py

@@ -71,11 +71,15 @@ def should_show_dropdown(self, search_string: str) -> bool:  # noqa: ARG002
         return not _is_exact_command_match(command_prefix)
 
     def get_candidates(self, target_state: TargetState) -> list[DropdownItem]:
-        """Return command candidates for current search."""
-        if not target_state.text.startswith(COMMAND_PREFIX):
+        """Return command candidates only while editing the slash-command name."""
+        command_prefix = _get_command_search_prefix(
+            target_state.text,
+            target_state.cursor_position,
+        )
+        if command_prefix is None:
             return []
 
-        search = self.get_search_string(target_state).lower()
+        search = command_prefix.lower()
         return [
             DropdownItem(main=f"{COMMAND_PREFIX}{name}{COMMAND_DESCRIPTION_SEPARATOR}{desc}")
             for name, desc in _COMMAND_ITEMS

tests/unit/ui/test_command_autocomplete.py

@@ -11,7 +11,9 @@
 
 async def _type_text(pilot, text: str) -> None:
     for character in text:
-        await pilot.press(character)
+        key = "space" if character == " " else character
+        await pilot.press(key)
+
 
 
 @pytest.mark.parametrize("command_name", ["help", "compact"])
@@ -47,3 +49,17 @@ async def test_exact_match_enter_submits_slash_command() -> None:
         assert app.editor.value == ""
         assert len(app.chat_container.children) == initial_message_count + 1
         assert isinstance(app.chat_container.children[-1].renderable, Table)
+
+
+async def test_command_autocomplete_ignores_slash_command_arguments() -> None:
+    app = TextualReplApp(state_manager=StateManager())
+
+    async with app.run_test(headless=True) as pilot:
+        autocomplete = app.query_one(CommandAutoComplete)
+
+        await _type_text(pilot, "/skills de")
+        await pilot.pause()
+
+        assert app.editor.value == "/skills de"
+        assert autocomplete.option_list.option_count == 0
+        assert autocomplete.display is False

tests/unit/ui/test_skills_autocomplete.py

@@ -7,6 +7,7 @@
 from tunacode.core.session import StateManager
 
 from tunacode.ui.app import TextualReplApp
+from tunacode.ui.widgets.command_autocomplete import CommandAutoComplete
 from tunacode.ui.widgets.skills_autocomplete import SkillsAutoComplete
 
 SKILL_TEMPLATE = """---
@@ -136,6 +137,52 @@ async def test_skills_autocomplete_enter_prefers_best_prefix_match(
         assert app.state_manager.session.selected_skill_names == ["demo"]
 
 
+async def test_skills_autocomplete_down_selects_highlighted_skill(
+    tmp_path: Path,
+    monkeypatch,
+) -> None:
+    monkeypatch.chdir(tmp_path)
+    monkeypatch.setenv("HOME", str(tmp_path / "home"))
+    _write_skill(tmp_path, "alpha", description="Alpha skill")
+    _write_skill(tmp_path, "beta", description="Beta skill")
+
+    app = TextualReplApp(state_manager=StateManager())
+
+    async with app.run_test(headless=True) as pilot:
+        command_autocomplete = app.query_one(CommandAutoComplete)
+        skills_autocomplete = app.query_one(SkillsAutoComplete)
+
+        await _type_text(pilot, "/skills ")
+        await pilot.pause()
+
+        assert app.editor.value == "/skills "
+        assert command_autocomplete.option_list.option_count == 0
+        assert command_autocomplete.display is False
+        assert skills_autocomplete.display is True
+
+        await pilot.press("down")
+        await pilot.press("down")
+        await pilot.press("down")
+        await pilot.pause()
+
+        highlighted_index = skills_autocomplete.option_list.highlighted
+        assert highlighted_index == 3
+        highlighted_option = skills_autocomplete.option_list.get_option_at_index(highlighted_index)
+        assert highlighted_option.value == "alpha"
+
+        await pilot.press("enter")
+        await pilot.pause()
+
+        assert app.editor.value == "/skills alpha"
+        assert command_autocomplete.display is False
+
+        await pilot.press("enter")
+        await pilot.pause()
+
+        assert app.editor.value == ""
+        assert app.state_manager.session.selected_skill_names == ["alpha"]
+
+
 async def _type_text(pilot, text: str) -> None:
     for character in text:
         key = "space" if character == " " else character