fix: prevent extension command shadowing (#1994)

* fix: prevent extension command shadowing

* Validate extension command namespaces

* Reuse extension command name pattern

src/specify_cli/extensions.py

@@ -25,6 +25,49 @@ import yaml
 from packaging import version as pkg_version
 from packaging.specifiers import SpecifierSet, InvalidSpecifier
 
+_FALLBACK_CORE_COMMAND_NAMES = frozenset({
+    "analyze",
+    "checklist",
+    "clarify",
+    "constitution",
+    "implement",
+    "plan",
+    "specify",
+    "tasks",
+    "taskstoissues",
+})
+EXTENSION_COMMAND_NAME_PATTERN = re.compile(r"^speckit\.([a-z0-9-]+)\.([a-z0-9-]+)$")
+
+
+def _load_core_command_names() -> frozenset[str]:
+    """Discover bundled core command names from the packaged templates.
+
+    Prefer the wheel-time ``core_pack`` bundle when present, and fall back to
+    the source checkout when running from the repository. If neither is
+    available, use the baked-in fallback set so validation still works.
+    """
+    candidate_dirs = [
+        Path(__file__).parent / "core_pack" / "commands",
+        Path(__file__).resolve().parent.parent.parent / "templates" / "commands",
+    ]
+
+    for commands_dir in candidate_dirs:
+        if not commands_dir.is_dir():
+            continue
+
+        command_names = {
+            command_file.stem
+            for command_file in commands_dir.iterdir()
+            if command_file.is_file() and command_file.suffix == ".md"
+        }
+        if command_names:
+            return frozenset(command_names)
+
+    return _FALLBACK_CORE_COMMAND_NAMES
+
+
+CORE_COMMAND_NAMES = _load_core_command_names()
+
 
 class ExtensionError(Exception):
     """Base exception for extension-related errors."""
@@ -149,7 +192,7 @@ class ExtensionManifest:
                 raise ValidationError("Command missing 'name' or 'file'")
 
             # Validate command name format
-            if not re.match(r'^speckit\.[a-z0-9-]+\.[a-z0-9-]+$', cmd["name"]):
+            if EXTENSION_COMMAND_NAME_PATTERN.match(cmd["name"]) is None:
                 raise ValidationError(
                     f"Invalid command name '{cmd['name']}': "
                     "must follow pattern 'speckit.{extension}.{command}'"
@@ -446,6 +489,126 @@ class ExtensionManager:
         self.extensions_dir = project_root / ".specify" / "extensions"
         self.registry = ExtensionRegistry(self.extensions_dir)
 
+    @staticmethod
+    def _collect_manifest_command_names(manifest: ExtensionManifest) -> Dict[str, str]:
+        """Collect command and alias names declared by a manifest.
+
+        Performs install-time validation for extension-specific constraints:
+        - commands and aliases must use the canonical `speckit.{extension}.{command}` shape
+        - commands and aliases must use this extension's namespace
+        - command namespaces must not shadow core commands
+        - duplicate command/alias names inside one manifest are rejected
+
+        Args:
+            manifest: Parsed extension manifest
+
+        Returns:
+            Mapping of declared command/alias name -> kind ("command"/"alias")
+
+        Raises:
+            ValidationError: If any declared name is invalid
+        """
+        if manifest.id in CORE_COMMAND_NAMES:
+            raise ValidationError(
+                f"Extension ID '{manifest.id}' conflicts with core command namespace '{manifest.id}'"
+            )
+
+        declared_names: Dict[str, str] = {}
+
+        for cmd in manifest.commands:
+            primary_name = cmd["name"]
+            aliases = cmd.get("aliases", [])
+
+            if aliases is None:
+                aliases = []
+            if not isinstance(aliases, list):
+                raise ValidationError(
+                    f"Aliases for command '{primary_name}' must be a list"
+                )
+
+            for kind, name in [("command", primary_name)] + [
+                ("alias", alias) for alias in aliases
+            ]:
+                if not isinstance(name, str):
+                    raise ValidationError(
+                        f"{kind.capitalize()} for command '{primary_name}' must be a string"
+                    )
+
+                match = EXTENSION_COMMAND_NAME_PATTERN.match(name)
+                if match is None:
+                    raise ValidationError(
+                        f"Invalid {kind} '{name}': "
+                        "must follow pattern 'speckit.{extension}.{command}'"
+                    )
+
+                namespace = match.group(1)
+                if namespace != manifest.id:
+                    raise ValidationError(
+                        f"{kind.capitalize()} '{name}' must use extension namespace '{manifest.id}'"
+                    )
+
+                if namespace in CORE_COMMAND_NAMES:
+                    raise ValidationError(
+                        f"{kind.capitalize()} '{name}' conflicts with core command namespace '{namespace}'"
+                    )
+
+                if name in declared_names:
+                    raise ValidationError(
+                        f"Duplicate command or alias '{name}' in extension manifest"
+                    )
+
+                declared_names[name] = kind
+
+        return declared_names
+
+    def _get_installed_command_name_map(
+        self,
+        exclude_extension_id: Optional[str] = None,
+    ) -> Dict[str, str]:
+        """Return registered command and alias names for installed extensions."""
+        installed_names: Dict[str, str] = {}
+
+        for ext_id in self.registry.keys():
+            if ext_id == exclude_extension_id:
+                continue
+
+            manifest = self.get_extension(ext_id)
+            if manifest is None:
+                continue
+
+            for cmd in manifest.commands:
+                cmd_name = cmd.get("name")
+                if isinstance(cmd_name, str):
+                    installed_names.setdefault(cmd_name, ext_id)
+
+                aliases = cmd.get("aliases", [])
+                if not isinstance(aliases, list):
+                    continue
+
+                for alias in aliases:
+                    if isinstance(alias, str):
+                        installed_names.setdefault(alias, ext_id)
+
+        return installed_names
+
+    def _validate_install_conflicts(self, manifest: ExtensionManifest) -> None:
+        """Reject installs that would shadow core or installed extension commands."""
+        declared_names = self._collect_manifest_command_names(manifest)
+        installed_names = self._get_installed_command_name_map(
+            exclude_extension_id=manifest.id
+        )
+
+        collisions = [
+            f"{name} (already provided by extension '{installed_names[name]}')"
+            for name in sorted(declared_names)
+            if name in installed_names
+        ]
+        if collisions:
+            raise ValidationError(
+                "Extension commands conflict with installed extensions:\n- "
+                + "\n- ".join(collisions)
+            )
+
     @staticmethod
     def _load_extensionignore(source_dir: Path) -> Optional[Callable[[str, List[str]], Set[str]]]:
         """Load .extensionignore and return an ignore function for shutil.copytree.
@@ -861,6 +1024,9 @@ class ExtensionManager:
                 f"Use 'specify extension remove {manifest.id}' first."
             )
 
+        # Reject manifests that would shadow core commands or installed extensions.
+        self._validate_install_conflicts(manifest)
+
         # Install extension
         dest_dir = self.extensions_dir / manifest.id
         if dest_dir.exists():