diff --git a/src/specify_cli/__init__.py b/src/specify_cli/__init__.py
index d3eb36391e..efc8f3424d 100644
--- a/src/specify_cli/__init__.py
+++ b/src/specify_cli/__init__.py
@@ -4874,6 +4874,10 @@ def extension_update(
         failed_updates = []
         registrar = CommandRegistrar()
         hook_executor = HookExecutor(project_root)
+        from .agents import CommandRegistrar as _AgentReg  # used in backup and rollback paths
+
+        # UNSET sentinel: backup not yet captured (exception before backup step)
+        UNSET = object()
 
         for update in updates_available:
             extension_id = update["id"]
@@ -4887,8 +4891,9 @@ def extension_update(
             backup_config_dir = backup_base / "config"
 
             # Store backup state
-            backup_registry_entry = None
-            backup_hooks = None  # None means no hooks key in config; {} means hooks key existed
+            backup_registry_entry = None  # None means registry entry not yet captured
+            backup_installed = UNSET  # Original installed list from extensions.yml
+            backup_hooks = None  # None means backup step 4 not yet reached; {} or {...} means backup was captured
             backed_up_command_files = {}
 
             try:
@@ -4913,8 +4918,7 @@ def extension_update(
                         shutil.copy2(cfg_file, backup_config_dir / cfg_file.name)
 
                 # 3. Backup command files for all agents
-                from .agents import CommandRegistrar as _AgentReg
-                registered_commands = backup_registry_entry.get("registered_commands", {})
+                registered_commands = backup_registry_entry.get("registered_commands", {}) if isinstance(backup_registry_entry, dict) else {}
                 for agent_name, cmd_names in registered_commands.items():
                     if agent_name not in registrar.AGENT_CONFIGS:
                         continue
@@ -4939,14 +4943,20 @@ def extension_update(
                                 shutil.copy2(prompt_file, backup_prompt_path)
                                 backed_up_command_files[str(prompt_file)] = str(backup_prompt_path)
 
-                # 4. Backup hooks from extensions.yml
-                # Use backup_hooks=None to indicate config had no "hooks" key (don't create on restore)
-                # Use backup_hooks={} to indicate config had "hooks" key with no hooks for this extension
+                # 4. Backup hooks and installed list from extensions.yml
+                # get_project_config() always normalizes installed->[] and hooks->{},
+                # so no sentinel is needed to distinguish key-absent from key-empty.
                 config = hook_executor.get_project_config()
-                if "hooks" in config:
-                    backup_hooks = {}  # Config has hooks key - preserve this fact
-                    for hook_name, hook_list in config["hooks"].items():
-                        ext_hooks = [h for h in hook_list if h.get("extension") == extension_id]
+                if isinstance(config, dict):
+                    import copy
+                    # Deep-copy so nested mapping entries (e.g. version-pin dicts)
+                    # are not affected by in-place mutations during the update.
+                    backup_installed = copy.deepcopy(config.get("installed", []))
+                    backup_hooks = {}
+                    for hook_name, hook_list in config.get("hooks", {}).items():
+                        if not isinstance(hook_list, list):
+                            continue
+                        ext_hooks = [h for h in hook_list if isinstance(h, dict) and h.get("extension") == extension_id]
                         if ext_hooks:
                             backup_hooks[hook_name] = ext_hooks
 
@@ -5099,35 +5109,51 @@ def extension_update(
                             original_file.parent.mkdir(parents=True, exist_ok=True)
                             shutil.copy2(backup_file, original_file)
 
-                    # Restore hooks in extensions.yml
-                    # - backup_hooks=None means original config had no "hooks" key
-                    # - backup_hooks={} or {...} means config had hooks key
-                    config = hook_executor.get_project_config()
-                    if "hooks" in config:
+                    # Restore metadata in extensions.yml (hooks and installed list).
+                    # Only run if backup step 4 was reached (backup_hooks is not None);
+                    # otherwise we have no safe baseline to restore from and could corrupt
+                    # the config by removing pre-existing hooks.
+                    if backup_hooks is not None:
+                        config = hook_executor.get_project_config()
+                        if not isinstance(config, dict):
+                            config = {}
+
                         modified = False
 
-                        if backup_hooks is None:
-                            # Original config had no "hooks" key; remove it entirely
-                            del config["hooks"]
+                        # 1. Restore hooks in extensions.yml
+                        if not isinstance(config.get("hooks"), dict):
+                            config["hooks"] = {}
                             modified = True
-                        else:
-                            # Remove any hooks for this extension added by failed install
-                            for hook_name, hooks_list in config["hooks"].items():
-                                original_len = len(hooks_list)
-                                config["hooks"][hook_name] = [
-                                    h for h in hooks_list
-                                    if h.get("extension") != extension_id
-                                ]
-                                if len(config["hooks"][hook_name]) != original_len:
-                                    modified = True
-
-                            # Add back the backed up hooks if any
-                            if backup_hooks:
-                                for hook_name, hooks in backup_hooks.items():
-                                    if hook_name not in config["hooks"]:
-                                        config["hooks"][hook_name] = []
-                                    config["hooks"][hook_name].extend(hooks)
-                                    modified = True
+
+                        # Remove any hooks for this extension added by the failed install
+                        for hook_name in list(config["hooks"].keys()):
+                            hooks_list = config["hooks"][hook_name]
+                            if not isinstance(hooks_list, list):
+                                config["hooks"][hook_name] = []
+                                modified = True
+                                continue
+
+                            original_len = len(hooks_list)
+                            config["hooks"][hook_name] = [
+                                h for h in hooks_list
+                                if isinstance(h, dict) and h.get("extension") != extension_id
+                            ]
+                            if len(config["hooks"][hook_name]) != original_len:
+                                modified = True
+
+                        # Add back the backed-up hooks
+                        if backup_hooks:
+                            for hook_name, hooks in backup_hooks.items():
+                                if not isinstance(config["hooks"].get(hook_name), list):
+                                    config["hooks"][hook_name] = []
+                                config["hooks"][hook_name].extend(hooks)
+                                modified = True
+
+                        # 2. Restore installed list in extensions.yml
+                        if backup_installed is not UNSET:
+                            if config.get("installed") != backup_installed:
+                                config["installed"] = backup_installed
+                                modified = True
 
                         if modified:
                             hook_executor.save_project_config(config)
diff --git a/src/specify_cli/extensions.py b/src/specify_cli/extensions.py
index 944ee4a06d..f657de06ce 100644
--- a/src/specify_cli/extensions.py
+++ b/src/specify_cli/extensions.py
@@ -1190,7 +1190,7 @@ def install_from_directory(
         # was used during project initialisation (feature parity).
         registered_skills = self._register_extension_skills(manifest, dest_dir)
 
-        # Register hooks
+        # Register hooks and update installed list in extensions.yml
         hook_executor = HookExecutor(self.project_root)
         hook_executor.register_hooks(manifest)
 
@@ -2481,7 +2481,32 @@ def get_project_config(self) -> Dict[str, Any]:
             }
 
         try:
-            return yaml.safe_load(self.config_file.read_text(encoding="utf-8")) or {}
+            result = yaml.safe_load(self.config_file.read_text(encoding="utf-8"))
+            # Coerce non-dict root (including None for an empty file) to the
+            # fully-normalized default so callers always get guaranteed fields.
+            if not isinstance(result, dict):
+                return {
+                    "installed": [],
+                    "settings": {"auto_execute_hooks": True},
+                    "hooks": {},
+                }
+            # Normalize nested fields so read-only callers like get_hooks_for_event()
+            # never see non-dict hooks or non-list installed (Feedback)
+            if not isinstance(result.get("hooks"), dict):
+                result["hooks"] = {}
+            if not isinstance(result.get("installed"), list):
+                result["installed"] = []
+            if not isinstance(result.get("settings"), dict):
+                result["settings"] = {"auto_execute_hooks": True}
+            # Sanitize hook event values: coerce non-list values to [] and filter
+            # non-dict items so get_hooks_for_event() can safely call .get() (Feedback)
+            for event_key in list(result["hooks"]):
+                event_val = result["hooks"][event_key]
+                if not isinstance(event_val, list):
+                    result["hooks"][event_key] = []
+                else:
+                    result["hooks"][event_key] = [h for h in event_val if isinstance(h, dict)]
+            return result
         except (yaml.YAMLError, OSError, UnicodeError):
             return {
                 "installed": [],
@@ -2501,25 +2526,141 @@ def save_project_config(self, config: Dict[str, Any]):
             encoding="utf-8",
         )
 
+    def register_extension(self, extension_id: str):
+        """Add extension to the installed list in project config.
+
+        Args:
+            extension_id: ID of extension to register
+        """
+        config = self.get_project_config()
+
+        # Ensure config is a dict (defensive)
+        if not isinstance(config, dict):
+            config = {}
+
+        raw_installed = config.get("installed")
+        sanitized = self._sanitize_installed_list(raw_installed, add_id=extension_id)
+
+        if sanitized != raw_installed:
+            config["installed"] = sanitized
+            self.save_project_config(config)
+
+    def unregister_extension(self, extension_id: str):
+        """Remove extension from the installed list in project config.
+
+        Args:
+            extension_id: ID of extension to unregister
+        """
+        config = self.get_project_config()
+
+        if not isinstance(config, dict):
+            config = {}
+
+        raw_installed = config.get("installed")
+        sanitized = self._sanitize_installed_list(raw_installed, remove_id=extension_id)
+
+        # Always persist if sanitized state differs from raw config (ensures normalization)
+        if sanitized != raw_installed:
+            config["installed"] = sanitized
+            self.save_project_config(config)
+
+    @staticmethod
+    def _sanitize_installed_list(
+        raw: object,
+        *,
+        add_id: str = "",
+        remove_id: str = "",
+    ) -> list:
+        """Normalize, deduplicate, and optionally add/remove an extension id.
+
+        Shared by register_extension() and unregister_extension() to prevent
+        the two paths from drifting.
+
+        Args:
+            raw: The raw value from config["installed"] (may be non-list).
+            add_id: If non-empty, ensure this id is present (plain-string fallback).
+            remove_id: If non-empty, remove this id from the list.
+
+        Returns:
+            A sanitized, deduplicated, alphabetically-sorted list.
+        """
+        _VALID_ID = re.compile(r'^[a-z0-9-]+$')
+
+        installed = raw if isinstance(raw, list) else []
+
+        # Keep only entries whose resolved id is a non-empty string matching
+        # the extension-id format (^[a-z0-9-]+$), same rule ExtensionManifest enforces.
+        def _valid_entry(x: object) -> bool:
+            if isinstance(x, str):
+                return bool(_VALID_ID.match(x.strip()))
+            if isinstance(x, dict):
+                eid = x.get("id")
+                return isinstance(eid, str) and bool(_VALID_ID.match(eid.strip()))
+            return False
+
+        valid = [x for x in installed if _valid_entry(x)]
+
+        # Deduplicate by id: prefer dict (richer metadata) over plain string
+        seen: dict = {}  # id -> entry (dict preferred over str)
+        for x in valid:
+            eid = x.strip() if isinstance(x, str) else x.get("id", "").strip()
+            if eid not in seen or isinstance(x, dict):
+                seen[eid] = x
+
+        # Validate add_id against the same regex before inserting
+        if add_id and _VALID_ID.match(add_id.strip()) and add_id not in seen:
+            seen[add_id] = add_id
+
+        if remove_id:
+            seen.pop(remove_id, None)
+
+        def _sort_key(x: object) -> str:
+            return x if isinstance(x, str) else x.get("id", "")  # type: ignore[return-value]
+
+        return sorted(seen.values(), key=_sort_key)
+
     def register_hooks(self, manifest: ExtensionManifest):
         """Register extension hooks in project config.
 
         Args:
             manifest: Extension manifest with hooks to register
         """
+        # Always ensure the extension is in the installed list
+        self.register_extension(manifest.id)
+
         if not hasattr(manifest, "hooks") or not manifest.hooks:
             return
 
         config = self.get_project_config()
 
-        # Ensure hooks dict exists
-        if "hooks" not in config:
+        # Ensure config is a dict (defensive)
+        changed = False
+        if not isinstance(config, dict):
+            config = {}
+            changed = True
+
+        # Ensure hooks dict exists and is a mapping
+        if "hooks" not in config or not isinstance(config["hooks"], dict):
             config["hooks"] = {}
+            changed = True
+        else:
+            # Sanitize existing hook lists to prevent crashes in downstream code (Feedback)
+            for h_name in list(config["hooks"].keys()):
+                h_list = config["hooks"][h_name]
+                if not isinstance(h_list, list):
+                    config["hooks"][h_name] = []
+                    changed = True
+                else:
+                    sanitized_h_list = [h for h in h_list if isinstance(h, dict)]
+                    if len(sanitized_h_list) != len(h_list):
+                        config["hooks"][h_name] = sanitized_h_list
+                        changed = True
 
         # Register each hook
         for hook_name, hook_config in manifest.hooks.items():
-            if hook_name not in config["hooks"]:
+            if hook_name not in config["hooks"] or not isinstance(config["hooks"][hook_name], list):
                 config["hooks"][hook_name] = []
+                changed = True
 
             # Add hook entry
             hook_entry = {
@@ -2534,22 +2675,22 @@ def register_hooks(self, manifest: ExtensionManifest):
                 "condition": hook_config.get("condition"),
             }
 
-            # Check if already registered
-            existing = [
-                h
-                for h in config["hooks"][hook_name]
-                if h.get("extension") == manifest.id
+            # Deduplicate: remove all existing entries for this extension on this
+            # hook event, then append the single canonical entry. This prevents
+            # multiple hooks firing when hand-edited or older versions leave
+            # duplicate entries behind. (Feedback from review)
+            original_list = config["hooks"][hook_name]
+            deduped = [
+                h for h in original_list
+                if not (isinstance(h, dict) and h.get("extension") == manifest.id)
             ]
+            deduped.append(hook_entry)
+            if deduped != original_list:
+                config["hooks"][hook_name] = deduped
+                changed = True
 
-            if not existing:
-                config["hooks"][hook_name].append(hook_entry)
-            else:
-                # Update existing
-                for i, h in enumerate(config["hooks"][hook_name]):
-                    if h.get("extension") == manifest.id:
-                        config["hooks"][hook_name][i] = hook_entry
-
-        self.save_project_config(config)
+        if changed:
+            self.save_project_config(config)
 
     def unregister_hooks(self, extension_id: str):
         """Remove extension hooks from project config.
@@ -2557,17 +2698,30 @@ def unregister_hooks(self, extension_id: str):
         Args:
             extension_id: ID of extension to unregister
         """
+        # Always remove from installed list (Feedback from review)
+        self.unregister_extension(extension_id)
+
         config = self.get_project_config()
 
-        if "hooks" not in config:
+        if not isinstance(config, dict):
+            config = {}
+            # We don't save yet, as there are no hooks to unregister, 
+            # but unregister_extension above might have already saved a normalized config.
+            return
+
+        if "hooks" not in config or not isinstance(config["hooks"], dict):
             return
 
         # Remove hooks for this extension
-        for hook_name in config["hooks"]:
+        for hook_name in list(config["hooks"].keys()):
+            hook_list = config["hooks"][hook_name]
+            if not isinstance(hook_list, list):
+                config["hooks"][hook_name] = []
+                continue
             config["hooks"][hook_name] = [
                 h
-                for h in config["hooks"][hook_name]
-                if h.get("extension") != extension_id
+                for h in hook_list
+                if isinstance(h, dict) and h.get("extension") != extension_id
             ]
 
         # Clean up empty hook arrays
diff --git a/tests/test_extension_registration.py b/tests/test_extension_registration.py
new file mode 100644
index 0000000000..9965deae43
--- /dev/null
+++ b/tests/test_extension_registration.py
@@ -0,0 +1,497 @@
+import pytest
+import yaml
+from specify_cli.extensions import HookExecutor, ExtensionManifest
+
+@pytest.fixture
+def project_dir(tmp_path):
+    """Create a mock spec-kit project directory."""
+    proj_dir = tmp_path / "project"
+    proj_dir.mkdir()
+    (proj_dir / ".specify").mkdir()
+    return proj_dir
+
+class TestExtensionRegistration:
+    """Tests for the 'installed' list management in HookExecutor."""
+
+    def test_register_extension_new(self, project_dir):
+        """Standard registration: Adding an extension should add it to the list."""
+        executor = HookExecutor(project_dir)
+        executor.register_extension("test-ext")
+        
+        config = executor.get_project_config()
+        assert "installed" in config
+        assert config["installed"] == ["test-ext"]
+
+    def test_register_extension_sorting(self, project_dir):
+        """Order Stability: Extensions should be stored in alphabetical order."""
+        executor = HookExecutor(project_dir)
+        executor.register_extension("zebra-ext")
+        executor.register_extension("apple-ext")
+        executor.register_extension("middle-ext")
+        
+        config = executor.get_project_config()
+        assert config["installed"] == ["apple-ext", "middle-ext", "zebra-ext"]
+
+    def test_register_extension_idempotency(self, project_dir):
+        """Idempotency: Adding the same extension twice should not result in duplicates."""
+        executor = HookExecutor(project_dir)
+        executor.register_extension("test-ext")
+        executor.register_extension("test-ext")
+        
+        config = executor.get_project_config()
+        assert config["installed"] == ["test-ext"]
+        assert len(config["installed"]) == 1
+
+    def test_unregister_extension(self, project_dir):
+        """Standard unregistration: Removing an extension should prune it from the list."""
+        executor = HookExecutor(project_dir)
+        executor.register_extension("ext-1")
+        executor.register_extension("ext-2")
+        
+        executor.unregister_extension("ext-1")
+        
+        config = executor.get_project_config()
+        assert config["installed"] == ["ext-2"]
+
+    def test_unregister_extension_not_present(self, project_dir):
+        """Safe Removal: Unregistering a non-existent extension should do nothing."""
+        executor = HookExecutor(project_dir)
+        executor.register_extension("ext-1")
+        
+        # Should not raise or change the list
+        executor.unregister_extension("ext-nonexistent")
+        
+        config = executor.get_project_config()
+        assert config["installed"] == ["ext-1"]
+
+    def test_register_hooks_triggers_registration(self, project_dir, tmp_path):
+        """Full Workflow: register_hooks should automatically register the extension."""
+        # Create a mock manifest
+        manifest_data = {
+            "schema_version": "1.0",
+            "extension": {
+                "id": "hook-ext",
+                "name": "Hook Ext",
+                "version": "1.0.0",
+                "description": "Test",
+            },
+            "requires": {
+                "speckit_version": ">=0.1.0",
+                "commands": []
+            },
+            "provides": {"commands": []},
+            "hooks": {
+                "after_tasks": {"command": "speckit.hook-ext.run"}
+            }
+        }
+        manifest_path = tmp_path / "extension.yml"
+        with open(manifest_path, "w") as f:
+            yaml.dump(manifest_data, f)
+        
+        manifest = ExtensionManifest(manifest_path)
+        executor = HookExecutor(project_dir)
+        
+        # This should call register_extension internally
+        executor.register_hooks(manifest)
+        
+        config = executor.get_project_config()
+        assert "hook-ext" in config["installed"]
+
+    def test_missing_installed_key_initialization(self, project_dir):
+        """Graceful Initialization: If 'installed' key is missing, it should be created."""
+        executor = HookExecutor(project_dir)
+        
+        # Manually create a config without 'installed'
+        config_path = project_dir / ".specify" / "extensions.yml"
+        config_path.write_text(yaml.dump({"settings": {"auto_execute_hooks": True}}))
+        
+        # This should detect the missing key and initialize it
+        executor.register_extension("new-ext")
+        
+        config = executor.get_project_config()
+        assert "installed" in config
+        assert config["installed"] == ["new-ext"]
+
+    def test_unregister_hooks_full_workflow(self, project_dir, tmp_path):
+        """Full Workflow: unregister_hooks should remove hooks and prune installed list."""
+        # Create a manifest with hooks
+        manifest_data = {
+            "schema_version": "1.0",
+            "extension": {
+                "id": "hook-ext",
+                "name": "Hook Ext",
+                "version": "1.0.0",
+                "description": "Test",
+            },
+            "requires": {
+                "speckit_version": ">=0.1.0",
+                "commands": []
+            },
+            "provides": {"commands": []},
+            "hooks": {
+                "after_tasks": {"command": "speckit.hook-ext.run"}
+            }
+        }
+        manifest_path = tmp_path / "extension.yml"
+        with open(manifest_path, "w") as f:
+            yaml.dump(manifest_data, f)
+        
+        manifest = ExtensionManifest(manifest_path)
+        executor = HookExecutor(project_dir)
+        
+        # Register hooks first
+        executor.register_hooks(manifest)
+        
+        config = executor.get_project_config()
+        assert "hook-ext" in config["installed"]
+        assert "after_tasks" in config["hooks"]
+        
+        # Now unregister hooks
+        executor.unregister_hooks("hook-ext")
+        
+        config = executor.get_project_config()
+        assert "hook-ext" not in config["installed"]
+        # unregister_hooks() removes the empty hook array entirely, so the key is absent
+        assert "after_tasks" not in config["hooks"]
+
+    def test_unregister_hooks_no_hooks_key(self, project_dir):
+        """Resilience: unregister_hooks should work even if config has no 'hooks' key."""
+        executor = HookExecutor(project_dir)
+        
+        # Register extension without hooks
+        executor.register_extension("ext-no-hooks")
+        
+        config = executor.get_project_config()
+        assert "ext-no-hooks" in config["installed"]
+        
+        # Unregister should not crash even if no hooks key exists
+        executor.unregister_hooks("ext-no-hooks")
+        
+        config = executor.get_project_config()
+        assert "ext-no-hooks" not in config["installed"]
+
+    def test_unregister_hooks_corrupted_config(self, project_dir):
+        """Resilience: unregister_hooks should gracefully handle corrupted config."""
+        # Create a corrupted config (root is a list)
+        config_path = project_dir / ".specify" / "extensions.yml"
+        config_path.write_text(yaml.dump(["corrupted", "list"]))
+        
+        executor = HookExecutor(project_dir)
+        
+        # Should not raise even with corrupted config
+        executor.unregister_hooks("non-existent")
+        
+        # Config should remain as-is or be handled gracefully
+        config = executor.get_project_config()
+        # If it's corrupted, it's returned as-is or handled by defensive logic
+        assert config is not None
+
+    def test_unregister_hooks_with_multiple_extensions(self, project_dir, tmp_path):
+        """Multiple Extensions: unregister_hooks should only remove target extension's hooks."""
+        # Create two manifests
+        manifest_data_1 = {
+            "schema_version": "1.0",
+            "extension": {
+                "id": "ext-1",
+                "name": "Ext 1",
+                "version": "1.0.0",
+                "description": "Test 1",
+            },
+            "requires": {
+                "speckit_version": ">=0.1.0",
+                "commands": []
+            },
+            "provides": {"commands": []},
+            "hooks": {
+                "after_tasks": {"command": "speckit.ext-1.run"}
+            }
+        }
+        manifest_data_2 = {
+            "schema_version": "1.0",
+            "extension": {
+                "id": "ext-2",
+                "name": "Ext 2",
+                "version": "1.0.0",
+                "description": "Test 2",
+            },
+            "requires": {
+                "speckit_version": ">=0.1.0",
+                "commands": []
+            },
+            "provides": {"commands": []},
+            "hooks": {
+                "after_tasks": {"command": "speckit.ext-2.run"}
+            }
+        }
+        
+        manifest_path_1 = tmp_path / "extension1.yml"
+        manifest_path_2 = tmp_path / "extension2.yml"
+        with open(manifest_path_1, "w") as f:
+            yaml.dump(manifest_data_1, f)
+        with open(manifest_path_2, "w") as f:
+            yaml.dump(manifest_data_2, f)
+        
+        manifest1 = ExtensionManifest(manifest_path_1)
+        manifest2 = ExtensionManifest(manifest_path_2)
+        executor = HookExecutor(project_dir)
+        
+        # Register both extensions
+        executor.register_hooks(manifest1)
+        executor.register_hooks(manifest2)
+        
+        config = executor.get_project_config()
+        assert "ext-1" in config["installed"]
+        assert "ext-2" in config["installed"]
+        assert len(config["hooks"]["after_tasks"]) == 2
+        
+        # Unregister first extension
+        executor.unregister_hooks("ext-1")
+        
+        config = executor.get_project_config()
+        assert "ext-1" not in config["installed"]
+        assert "ext-2" in config["installed"]
+        # ext-2's hook should still be there
+        assert len(config["hooks"]["after_tasks"]) == 1
+        assert config["hooks"]["after_tasks"][0].get("extension") == "ext-2"
+
+    def test_register_hooks_no_hooks_still_registers(self, project_dir, tmp_path):
+        """Commands-only manifest: register_hooks() must still update installed even with no hooks."""
+        manifest_data = {
+            "schema_version": "1.0",
+            "extension": {
+                "id": "commands-only-ext",
+                "name": "Commands Only",
+                "version": "1.0.0",
+                "description": "No hooks, only commands",
+            },
+            "requires": {
+                "speckit_version": ">=0.1.0",
+                "commands": []
+            },
+            "provides": {"commands": [{"name": "speckit.commands-only-ext.run", "file": "commands/run.md"}]},
+        }
+        manifest_path = tmp_path / "extension.yml"
+        with open(manifest_path, "w") as f:
+            yaml.dump(manifest_data, f)
+
+        manifest = ExtensionManifest(manifest_path)
+        executor = HookExecutor(project_dir)
+        executor.register_hooks(manifest)
+
+        config = executor.get_project_config()
+        assert "commands-only-ext" in config["installed"]
+
+    def test_register_extension_mixed_type_installed(self, project_dir):
+        """Regression: installed list with non-string entries must not crash on sort."""
+        executor = HookExecutor(project_dir)
+
+        # Manually write a corrupted installed list with non-string entries
+        config_path = project_dir / ".specify" / "extensions.yml"
+        config_path.write_text(yaml.dump({"installed": [1, True, "existing-ext"]}))
+
+        # Should not raise TypeError on sort
+        executor.register_extension("new-ext")
+
+        config = executor.get_project_config()
+        # Non-string entries are dropped; valid strings are preserved
+        assert "existing-ext" in config["installed"]
+        assert "new-ext" in config["installed"]
+        assert 1 not in config["installed"]
+        assert True not in config["installed"]
+
+    def test_unregister_hooks_null_hook_values(self, project_dir):
+        """Regression: hooks: {after_tasks: null} must not crash in unregister_hooks()."""
+        executor = HookExecutor(project_dir)
+
+        # Manually write a config with null hook event value
+        config_path = project_dir / ".specify" / "extensions.yml"
+        config_path.write_text(yaml.dump({
+            "installed": ["broken-ext"],
+            "hooks": {"after_tasks": None}
+        }))
+
+        # Should not raise TypeError when iterating None
+        executor.unregister_hooks("broken-ext")
+
+        config = executor.get_project_config()
+        assert "broken-ext" not in config["installed"]
+
+    def test_register_hooks_corrupted_hook_values(self, project_dir, tmp_path):
+        """Regression: register_hooks() must handle non-list hook event values in config."""
+        executor = HookExecutor(project_dir)
+
+        # Manually write a config with null hook event value
+        config_path = project_dir / ".specify" / "extensions.yml"
+        config_path.write_text(yaml.dump({
+            "installed": ["some-ext"],
+            "hooks": {"after_tasks": None}
+        }))
+
+        # Create a manifest with a hook for the same event
+        manifest_data = {
+            "schema_version": "1.0",
+            "extension": {
+                "id": "new-ext",
+                "name": "New Ext",
+                "version": "1.0.0",
+                "description": "Test",
+            },
+            "requires": {
+                "speckit_version": ">=0.1.0",
+                "commands": []
+            },
+            "provides": {"commands": []},
+            "hooks": {"after_tasks": {"command": "speckit.new-ext.run"}}
+        }
+        manifest_path = tmp_path / "extension.yml"
+        with open(manifest_path, "w") as f:
+            yaml.dump(manifest_data, f)
+        
+        manifest = ExtensionManifest(manifest_path)
+        
+        # Should not raise TypeError when trying to append to None
+        executor.register_hooks(manifest)
+
+        config = executor.get_project_config()
+        assert "new-ext" in config["installed"]
+        assert isinstance(config["hooks"]["after_tasks"], list)
+        assert any(h["extension"] == "new-ext" for h in config["hooks"]["after_tasks"])
+
+    def test_register_extension_already_present_in_corrupted_list(self, project_dir):
+        """Regression: if extension is already present but list has non-strings, it must still be sanitized."""
+        executor = HookExecutor(project_dir)
+
+        # Extension is present, but list has garbage
+        config_path = project_dir / ".specify" / "extensions.yml"
+        config_path.write_text(yaml.dump({"installed": [1, "test-ext", True]}))
+
+        # This should trigger sanitization and save, even though "test-ext" is already there
+        executor.register_extension("test-ext")
+
+        config = executor.get_project_config()
+        assert config["installed"] == ["test-ext"]
+        # Verify it was actually saved to disk
+        raw_config = yaml.safe_load(config_path.read_text())
+        assert raw_config["installed"] == ["test-ext"]
+
+    def test_register_extension_with_dict_entry(self, project_dir):
+        """Review Feedback: register_extension should support and preserve dict entries."""
+        executor = HookExecutor(project_dir)
+        config_path = project_dir / ".specify" / "extensions.yml"
+        
+        # Setup config with a pinned extension (dict)
+        pinned_ext = {"id": "pinned-ext", "version": "1.0.0"}
+        config_path.write_text(yaml.dump({
+            "installed": [pinned_ext, "string-ext"]
+        }))
+        
+        # Register a new extension
+        executor.register_extension("new-ext")
+        
+        config = executor.get_project_config()
+        # Should contain all three, sorted by id: new-ext, pinned-ext, string-ext
+        assert config["installed"] == ["new-ext", pinned_ext, "string-ext"]
+
+    def test_unregister_extension_with_dict_entry(self, project_dir):
+        """Review Feedback: unregister_extension should support removing matching dict entries."""
+        executor = HookExecutor(project_dir)
+        config_path = project_dir / ".specify" / "extensions.yml"
+        
+        pinned_ext = {"id": "to-remove", "version": "1.0.0"}
+        config_path.write_text(yaml.dump({
+            "installed": [pinned_ext, "other-ext"]
+        }))
+        
+        # Unregister by ID
+        executor.unregister_extension("to-remove")
+        
+        config = executor.get_project_config()
+        assert config["installed"] == ["other-ext"]
+
+    def test_unregister_extension_corrupted_installed(self, project_dir):
+        """Hardening: unregister_extension should handle non-list installed key."""
+        executor = HookExecutor(project_dir)
+        config_path = project_dir / ".specify" / "extensions.yml"
+        
+        config_path.write_text(yaml.dump({
+            "installed": "not-a-list"
+        }))
+        
+        # Should not crash and should normalize to []
+        executor.unregister_extension("any-ext")
+        
+        config = executor.get_project_config()
+        assert config["installed"] == []
+    def test_register_hooks_mixed_type_hook_list(self, project_dir, tmp_path):
+        """Regression: register_hooks() must sanitize hook event lists by dropping non-dicts."""
+        executor = HookExecutor(project_dir)
+
+        config_path = project_dir / ".specify" / "extensions.yml"
+        config_path.write_text(yaml.dump({
+            "installed": ["some-ext"],
+            "hooks": {"after_tasks": [1, "corrupted", {"extension": "other", "command": "cmd"}]}
+        }))
+
+        manifest_path = tmp_path / "extension.yml"
+        manifest_data = {
+            "schema_version": "1.0",
+            "extension": {
+                "id": "new-ext",
+                "name": "New Ext",
+                "version": "1.0.0",
+                "description": "Test",
+                "author": "Test author"
+            },
+            "requires": {
+                "speckit_version": ">=0.1.0",
+                "commands": []
+            },
+            "provides": {"commands": []},
+            "hooks": {
+                "after_tasks": {"command": "new-cmd"}
+            }
+        }
+        manifest_path.write_text(yaml.dump(manifest_data))
+        manifest = ExtensionManifest(manifest_path)
+
+        executor.register_hooks(manifest)
+
+        config = executor.get_project_config()
+        hooks = config["hooks"]["after_tasks"]
+        
+        # Should have 2 valid dict hooks, and 0 non-dict items
+        assert len(hooks) == 2
+        assert all(isinstance(h, dict) for h in hooks)
+        assert any(h.get("extension") == "other" for h in hooks)
+        assert any(h.get("extension") == "new-ext" for h in hooks)
+
+    def test_unregister_extension_scalar_root(self, project_dir):
+        """Hardening: unregister_extension should handle scalar root config."""
+        executor = HookExecutor(project_dir)
+        config_path = project_dir / ".specify" / "extensions.yml"
+        
+        config_path.write_text(yaml.dump(123))
+        
+        # Should not crash and should normalize to {}
+        executor.unregister_extension("any-ext")
+        
+        config = executor.get_project_config()
+        assert isinstance(config, dict)
+        assert config["installed"] == []
+
+    def test_unregister_hooks_scalar_hook_values(self, project_dir):
+        """Regression: unregister_hooks() must handle scalar hook event values."""
+        executor = HookExecutor(project_dir)
+        config_path = project_dir / ".specify" / "extensions.yml"
+        
+        config_path.write_text(yaml.dump({
+            "installed": ["some-ext"],
+            "hooks": {"after_tasks": 123}
+        }))
+        
+        # Should not raise TypeError when iterating
+        executor.unregister_hooks("some-ext")
+        
+        config = executor.get_project_config()
+        assert "some-ext" not in config["installed"]
+        assert "after_tasks" not in config["hooks"]
diff --git a/tests/test_extension_update_hardening.py b/tests/test_extension_update_hardening.py
new file mode 100644
index 0000000000..426e5ec7e9
--- /dev/null
+++ b/tests/test_extension_update_hardening.py
@@ -0,0 +1,109 @@
+from specify_cli.extensions import ExtensionManager, ExtensionRegistry, ExtensionCatalog
+import pytest
+import yaml
+from typer.testing import CliRunner
+from specify_cli import app
+
+runner = CliRunner()
+
+@pytest.fixture
+def project_dir(tmp_path):
+    """Create a mock spec-kit project directory."""
+    proj_dir = tmp_path / "project"
+    proj_dir.mkdir()
+    (proj_dir / ".specify").mkdir()
+    # Create required files for a project
+    (proj_dir / ".specify" / "config.toml").write_text("ai = 'claude'")
+    return proj_dir
+
+def test_extension_update_corrupted_config_root(project_dir, monkeypatch):
+    """Regression: extension update must handle corrupted extensions.yml (root is scalar)."""
+    # chdir into project_dir so _require_specify_project() succeeds
+    monkeypatch.chdir(project_dir)
+    
+    # Corrupt extensions.yml
+    config_path = project_dir / ".specify" / "extensions.yml"
+    config_path.write_text(yaml.dump(123))
+    
+    # Mock ExtensionManager to return an installed extension for resolution
+    
+    monkeypatch.setattr(ExtensionManager, "list_installed", lambda self: [{"id": "test-ext", "name": "Test Ext", "version": "1.0.0"}])
+    monkeypatch.setattr(ExtensionRegistry, "get", lambda self, ext_id: {"version": "1.0.0", "enabled": True})
+    monkeypatch.setattr(ExtensionCatalog, "get_extension_info", lambda self, ext_id: {"id": "test-ext", "name": "Test Ext", "version": "1.1.0", "download_url": "https://example.com/ext.zip"})
+    
+    # Mock download_extension to avoid network calls; use tmp_path so the test is hermetic
+    # and returns a Path so zip_path.exists() / zip_path.unlink() work without AttributeError
+    mock_zip = project_dir / "mock.zip"
+    monkeypatch.setattr(ExtensionCatalog, "download_extension", lambda self, ext_id: mock_zip)
+    
+    # Mock confirmation to true
+    monkeypatch.setattr("typer.confirm", lambda _: True)
+    
+    # Run update
+    result = runner.invoke(app, ["extension", "update", "test-ext"], obj={"project_root": project_dir})
+    
+    # extension_update() catches exceptions internally and exits with code 1 on failure.
+    assert result.exit_code == 1
+    assert "AttributeError" not in result.output
+    assert not isinstance(result.exception, AttributeError)
+
+def test_extension_update_corrupted_hooks_value(project_dir, monkeypatch):
+    """Regression: extension update must handle non-dict 'hooks' in extensions.yml."""
+    monkeypatch.chdir(project_dir)
+    
+    config_path = project_dir / ".specify" / "extensions.yml"
+    config_path.write_text(yaml.dump({
+        "installed": ["test-ext"],
+        "hooks": ["not", "a", "dict"]
+    }))
+    
+    monkeypatch.setattr(ExtensionManager, "list_installed", lambda self: [{"id": "test-ext", "name": "Test Ext", "version": "1.0.0"}])
+    monkeypatch.setattr(ExtensionRegistry, "get", lambda self, ext_id: {"version": "1.0.0", "enabled": True})
+    monkeypatch.setattr(ExtensionCatalog, "get_extension_info", lambda self, ext_id: {"id": "test-ext", "name": "Test Ext", "version": "1.1.0", "download_url": "https://example.com/ext.zip"})
+    # Use tmp_path-scoped zip so the test is hermetic and returns a Path for zip_path.exists()
+    mock_zip = project_dir / "mock.zip"
+    monkeypatch.setattr(ExtensionCatalog, "download_extension", lambda self, ext_id: mock_zip)
+    monkeypatch.setattr("typer.confirm", lambda _: True)
+    
+    result = runner.invoke(app, ["extension", "update", "test-ext"], obj={"project_root": project_dir})
+    
+    # extension_update() catches exceptions internally and exits with code 1 on failure.
+    assert result.exit_code == 1
+    assert "AttributeError" not in result.output
+    assert not isinstance(result.exception, AttributeError)
+
+def test_extension_update_rollback_corrupted_config(project_dir, monkeypatch):
+    """Regression: extension update rollback must handle corrupted extensions.yml."""
+    monkeypatch.chdir(project_dir)
+    
+    config_path = project_dir / ".specify" / "extensions.yml"
+    # Write config with hooks: null; get_project_config() normalizes this to {}
+    # so the backup captures {} and the restored config will have hooks: {}.
+    config_path.write_text(yaml.dump({"installed": ["test-ext"], "hooks": None}))
+    
+    # Mock update process to fail after backup
+    monkeypatch.setattr(ExtensionManager, "list_installed", lambda self: [{"id": "test-ext", "name": "Test Ext", "version": "1.0.0"}])
+    monkeypatch.setattr(ExtensionRegistry, "get", lambda self, ext_id: {"version": "1.0.0", "enabled": True})
+    
+    # Force failure in download_extension to trigger rollback
+    def mock_download_fail(*args, **kwargs):
+        # Corrupt the config BEFORE rollback is triggered
+        config_path.write_text(yaml.dump("CORRUPTED"))
+        raise Exception("Download failed")
+        
+    monkeypatch.setattr(ExtensionCatalog, "get_extension_info", lambda self, ext_id: {"id": "test-ext", "name": "Test Ext", "version": "1.1.0", "download_url": "https://example.com/ext.zip"})
+    monkeypatch.setattr(ExtensionCatalog, "download_extension", mock_download_fail)
+    monkeypatch.setattr("typer.confirm", lambda _: True)
+    
+    result = runner.invoke(app, ["extension", "update", "test-ext"], obj={"project_root": project_dir})
+    
+    # Should handle Exception and NOT crash with AttributeError during rollback
+    assert result.exit_code == 1
+    assert "Download failed" in result.output
+    assert not isinstance(result.exception, AttributeError)
+    
+    # Verify hooks key was preserved (normalized to {} if it was null/corrupted)
+    restored_config = yaml.safe_load(config_path.read_text())
+    assert isinstance(restored_config, dict)
+    assert "hooks" in restored_config
+    assert restored_config["hooks"] == {}