fix(presets): tolerate non-UTF-8 legacy commands (#3896)

Assisted-by: GitHub Copilot (model: GPT-5.6 Sol, autonomous)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/specify_cli/presets/__init__.py

@@ -5297,7 +5297,7 @@ class PresetResolver:
                                         fm_strategy = fm_data.get("strategy")
                                         if isinstance(fm_strategy, str) and fm_strategy.lower() in VALID_PRESET_STRATEGIES:
                                             strategy = fm_strategy.lower()
-                        except (yaml.YAMLError, OSError):
+                        except (UnicodeDecodeError, yaml.YAMLError, OSError):
                             # Best-effort legacy frontmatter parsing: keep default
                             # strategy ("replace") when content is unreadable/invalid.
                             pass

tests/test_presets.py

@@ -11626,6 +11626,24 @@ class TestResolveContent:
 class TestCollectAllLayers:
     """Test PresetResolver.collect_all_layers() method."""
 
+    def test_non_utf8_legacy_command_keeps_replace_strategy(self, project_dir):
+        presets_dir = project_dir / ".specify" / "presets"
+        command_path = (
+            presets_dir / "legacy-pack" / "commands" / "speckit.legacy.md"
+        )
+        command_path.parent.mkdir(parents=True)
+        command_path.write_bytes(b"\xff\xfe")
+        PresetRegistry(presets_dir).add(
+            "legacy-pack", {"version": "1.0.0", "priority": 10}
+        )
+
+        layers = PresetResolver(project_dir).collect_all_layers(
+            "speckit.legacy", "command"
+        )
+
+        assert layers[0]["path"] == command_path
+        assert layers[0]["strategy"] == "replace"
+
     def test_single_core_layer(self, project_dir):
         """Test collecting layers with only core template."""
         resolver = PresetResolver(project_dir)