fix(skills): preserve non-ASCII characters in skill frontmatter (#2917)

* fix(skills): preserve non-ASCII chars in skill frontmatter

Skill SKILL.md frontmatter descriptions containing non-ASCII
characters were escaped to \uXXXX / \xXX sequences because
yaml.safe_dump() was called without allow_unicode=True.

- Add allow_unicode=True to the 7 skill/command frontmatter
  safe_dump sites (extensions, presets, claude integration)
- Add regression tests for the render and extension-install paths

Follows the approach of #1936; encoding="utf-8" is already set on
the affected write paths, so no encoding change is needed here.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* refactor(_utils): add dump_frontmatter helper

Centralize skill/command frontmatter YAML serialization into a single
_utils.dump_frontmatter helper so no call site can drop allow_unicode or
diverge on formatting. Route the 7 existing sites through it and drop a
now-unused local yaml import.

Switch the extension test fixtures to yaml.safe_dump for parity with the
production safe-dump/safe-load codepaths.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

tests/integrations/test_integration_claude.py

@@ -66,6 +66,16 @@ class TestClaudeIntegration:
         assert parsed["disable-model-invocation"] is False
         assert parsed["metadata"]["source"] == "templates/commands/plan.md"
 
+    def test_render_skill_unicode(self):
+        """Test rendering a skill preserves non-ASCII characters."""
+        integration = get_integration("claude")
+        rendered = integration._render_skill(
+            "constitution",
+            {"description": "Prüfe Konformität der Implementierung"},
+            "Body",
+        )
+        assert "Prüfe Konformität" in rendered
+
     def test_setup_upserts_context_section(self, tmp_path):
         integration = get_integration("claude")
         manifest = IntegrationManifest("claude", tmp_path)

tests/test_extension_skills.py

@@ -90,7 +90,7 @@ def _create_extension_dir(temp_dir: Path, ext_id: str = "test-ext") -> Path:
     }
 
     with open(ext_dir / "extension.yml", "w") as f:
-        yaml.dump(manifest_data, f)
+        yaml.safe_dump(manifest_data, f)
 
     commands_dir = ext_dir / "commands"
     commands_dir.mkdir()
@@ -119,6 +119,50 @@ def _create_extension_dir(temp_dir: Path, ext_id: str = "test-ext") -> Path:
     return ext_dir
 
 
+def _create_unicode_extension_dir(temp_dir: Path, ext_id: str = "uni-ext") -> Path:
+    """Create an extension whose command description contains non-ASCII characters."""
+    ext_dir = temp_dir / ext_id
+    ext_dir.mkdir()
+    description = "Prüfe Konformität der Implementierung"
+
+    manifest_data = {
+        "schema_version": "1.0",
+        "extension": {
+            "id": ext_id,
+            "name": "Unicode Extension",
+            "version": "1.0.0",
+            "description": description,
+        },
+        "requires": {"speckit_version": ">=0.1.0"},
+        "provides": {
+            "commands": [
+                {
+                    "name": f"speckit.{ext_id}.hello",
+                    "file": "commands/hello.md",
+                    "description": description,
+                },
+            ]
+        },
+    }
+
+    with open(ext_dir / "extension.yml", "w", encoding="utf-8") as f:
+        yaml.safe_dump(manifest_data, f, allow_unicode=True)
+
+    commands_dir = ext_dir / "commands"
+    commands_dir.mkdir()
+    (commands_dir / "hello.md").write_text(
+        "---\n"
+        f'description: "{description}"\n'
+        "---\n"
+        "\n"
+        "# Hello\n"
+        "\n"
+        "Body.\n",
+        encoding="utf-8",
+    )
+    return ext_dir
+
+
 def _can_create_symlink(temp_dir: Path) -> bool:
     """Return True when the current platform/user can create file symlinks."""
     target = temp_dir / "symlink-target.txt"
@@ -432,6 +476,18 @@ class TestExtensionSkillRegistration:
         parsed = yaml.safe_load(skill_file.read_text(encoding="utf-8").split("---", 2)[1])
         assert "argument-hint" not in parsed
 
+    def test_skill_md_unicode(self, skills_project, temp_dir):
+        """SKILL.md generation should preserve non-ASCII characters."""
+        project_dir, skills_dir = skills_project
+        ext_dir = _create_unicode_extension_dir(temp_dir)
+        manager = ExtensionManager(project_dir)
+        manager.install_from_directory(ext_dir, "0.1.0", register_commands=False)
+
+        skill_file = skills_dir / "speckit-uni-ext-hello" / "SKILL.md"
+        content = skill_file.read_text(encoding="utf-8")
+
+        assert "Prüfe Konformität" in content
+
     def test_no_skills_when_ai_skills_disabled(self, no_skills_project, extension_dir):
         """No skills should be created when ai_skills is false."""
         manager = ExtensionManager(no_skills_project)
@@ -692,7 +748,7 @@ class TestExtensionSkillRegistration:
             },
         }
         with open(ext_dir / "extension.yml", "w") as f:
-            yaml.dump(manifest_data, f)
+            yaml.safe_dump(manifest_data, f)
 
         (ext_dir / "commands").mkdir()
         (ext_dir / "commands" / "plan.md").write_text(
@@ -747,7 +803,7 @@ class TestExtensionSkillRegistration:
             },
         }
         with open(ext_dir / "extension.yml", "w") as f:
-            yaml.dump(manifest_data, f)
+            yaml.safe_dump(manifest_data, f)
 
         (ext_dir / "commands").mkdir()
         (ext_dir / "commands" / "exists.md").write_text(
@@ -1303,7 +1359,7 @@ class TestExtensionSkillEdgeCases:
             },
         }
         with open(ext_dir / "extension.yml", "w") as f:
-            yaml.dump(manifest_data, f)
+            yaml.safe_dump(manifest_data, f)
 
         (ext_dir / "commands").mkdir()
         (ext_dir / "commands" / "plain.md").write_text(
@@ -1390,7 +1446,7 @@ class TestExtensionSkillEdgeCases:
             },
         }
         with open(ext_dir / "extension.yml", "w") as f:
-            yaml.dump(manifest_data, f)
+            yaml.safe_dump(manifest_data, f)
 
         (ext_dir / "commands").mkdir()
         # Malformed YAML: invalid key-value syntax