Fix autocomplete crash from stale cursor locations

sqlit/domains/query/ui/mixins/autocomplete.py

@@ -86,15 +86,28 @@ def _apply_autocomplete(self: AutocompleteMixinHost) -> None:
         self._hide_autocomplete()
 
     def _location_to_offset(self, text: str, location: tuple[int, int]) -> int:
-        """Convert (row, col) location to text offset."""
+        """Convert (row, col) location to text offset.
+
+        TextArea cursor locations can briefly become stale while debounced
+        autocomplete callbacks are waiting to run. Clamp the location to the
+        current text so stale row values do not index past the available lines.
+        """
         row, col = location
         lines = text.split("\n")
-        offset = sum(len(lines[i]) + 1 for i in range(row))
-        offset += col
+
+        if row <= 0:
+            return max(0, min(col, len(lines[0]) if lines else 0))
+
+        if row >= len(lines):
+            return len(text)
+
+        offset = sum(len(line) + 1 for line in lines[:row])
+        offset += max(0, min(col, len(lines[row])))
         return min(offset, len(text))
 
     def _offset_to_location(self, text: str, offset: int) -> tuple[int, int]:
         """Convert text offset to (row, col) location."""
+        offset = max(0, min(offset, len(text)))
         lines = text.split("\n")
         current_offset = 0
         for row, line in enumerate(lines):

tests/unit/test_autocomplete_location.py

@@ -0,0 +1,25 @@
+"""Tests for autocomplete cursor location conversion."""
+
+from sqlit.domains.query.ui.mixins.autocomplete import AutocompleteMixin
+
+
+def test_location_to_offset_clamps_stale_row_to_end() -> None:
+    """A stale debounced cursor row should not crash on single-line text."""
+    mixin = AutocompleteMixin()
+
+    assert mixin._location_to_offset("SELECT * FROM users", (4, 0)) == len("SELECT * FROM users")
+
+
+def test_location_to_offset_clamps_column_to_current_line() -> None:
+    """Columns past the line end should clamp to the line length."""
+    mixin = AutocompleteMixin()
+
+    assert mixin._location_to_offset("SELECT\nFROM", (1, 99)) == len("SELECT\nFROM")
+
+
+def test_offset_to_location_clamps_offset_to_text_bounds() -> None:
+    """Offset conversion should keep cursor positions inside the document."""
+    mixin = AutocompleteMixin()
+
+    assert mixin._offset_to_location("SELECT", -10) == (0, 0)
+    assert mixin._offset_to_location("SELECT", 999) == (0, len("SELECT"))