fix: register extensions for the active integration only

docs/reference/integrations.md

@@ -88,6 +88,8 @@ Installs the specified integration into the current project. If another integrat
 
 Installing an additional integration does not change the default integration. Use `specify integration use <key>` to change the default.
 
+Installed extensions and presets are not registered for a non-default integration at install time — they follow the currently active (default) integration only. `specify integration use <key>` (or `switch <key>`) is what rescaffolds them for the newly active integration.
+
 > **Note:** All integration management commands require a project already initialized with `specify init`. To start a new project with a specific agent, use `specify init <project> --integration <key>` instead.
 
 **Version note:** Controlled multi-install support was introduced in Spec Kit 0.8.5. If `specify integration install <key>` says another integration is already installed and only suggests `switch` or `uninstall`, check your local CLI with `specify version` and upgrade it. Running a one-shot command such as `uvx --from git+https://github.com/github/spec-kit.git specify ...` uses a temporary copy for that command only; it does not update the persistent `specify` executable on your `PATH`.
@@ -121,7 +123,7 @@ specify integration switch <key>
 | `--refresh-shared-infra` | Also overwrite shared infrastructure files even if you customized them (otherwise customizations are preserved) |
 | `--integration-options`  | Options for the target integration when it is not already installed      |
 
-If the target integration is not already installed, equivalent to running `uninstall` followed by `install` in a single step. In this mode, `--force` controls whether modified files from the removed integration are deleted. If the target integration is already installed, `switch` only changes the default integration, like `use`; in this mode, `--force` controls whether managed shared templates are overwritten while the default changes. `--integration-options` is rejected for already-installed targets because changing integration options requires reinstalling managed files; run `upgrade <key> --integration-options ...` first, then `use <key>`.
+If the target integration is not already installed, equivalent to running `uninstall` followed by `install` in a single step. In this mode, `--force` controls whether modified files from the removed integration are deleted. If the target integration is already installed, `switch` only changes the default integration, like `use`; in this mode, `--force` controls whether managed shared templates are overwritten while the default changes. `--integration-options` is rejected for already-installed targets because changing integration options requires reinstalling managed files; run `upgrade <key> --integration-options ...` first, then `use <key>`. Like `use`, `switch` rescaffolds installed extensions and presets for the target integration once it becomes the default.
 
 ## Use an Installed Integration
 
@@ -135,6 +137,8 @@ specify integration use <key>
 
 Sets the default integration without uninstalling any other installed integrations. This also refreshes managed shared templates so command references match the new default integration's invocation style. Modified or untracked shared templates are preserved unless `--force` is used.
 
+`use` is also the activation point for installed extensions and presets: it re-registers every enabled extension's and preset's command overrides (and skills, for skills-mode agents) for the newly active integration, so artifacts installed while a different integration was active are rescaffolded here rather than at install time.
+
 ## Upgrade an Integration
 
 ```bash
@@ -149,6 +153,8 @@ specify integration upgrade [<key>]
 
 Reinstalls an installed integration with updated templates and commands (e.g., after upgrading Spec Kit). Defaults to the default integration; if a key is provided, it must be one of the installed integrations. Detects locally modified files and blocks the upgrade unless `--force` is used. Stale files from the previous install that are no longer needed are removed automatically. Shared templates stay aligned with the default integration even when upgrading a non-default integration.
 
+Enabled extensions and presets are re-registered only when upgrading the currently active (default) integration; upgrading a non-default integration does not touch its extension or preset artifacts — `use`/`switch` that integration afterward to rescaffold them.
+
 ## Report Integration Status
 
 ```bash
@@ -288,3 +294,7 @@ CLI-based integrations (like Claude Code, Gemini CLI) require the tool to be ins
 ### When should I use `upgrade` vs `switch`?
 
 Use `upgrade` when you've upgraded Spec Kit and want to refresh an installed integration's managed files. Use `switch` when you want to replace the current default with another integration; if the target is already installed, `switch` behaves like `use`.
+
+### Do extensions and presets I install apply to every installed integration?
+
+No. Extensions (`specify extension add`) and presets (`specify preset add`) register their command overrides for the currently active (default) integration only, even if other integrations are installed. A non-default integration does not receive those artifacts until it becomes the default: `specify integration use <key>` (or `switch <key>`) rescaffolds every enabled extension and preset for the newly active integration. `specify integration upgrade` follows the same rule — it only re-registers extensions and presets when upgrading the active integration.

docs/reference/presets.md

@@ -139,7 +139,7 @@ catalogs:
 
 Presets can provide command files, template files (like `plan-template.md`), and script files. Each file name is evaluated independently against the priority stack, so different files can come from different layers.
 
-Templates and scripts are looked up from the stack when Spec Kit needs them. Commands use the same stack for replacement and composition, but are materialized into detected agent directories instead of being re-resolved by agents. During preset install, Spec Kit registers command files for the preset being installed; post-install and post-removal reconciliation then recomputes and writes the effective command content for affected command names based on the active stack. Agents do not re-resolve the stack each time they run a command.
+Templates and scripts are looked up from the stack when Spec Kit needs them. Commands use the same stack for replacement and composition, but are materialized into the active integration's directory only, instead of being re-resolved by agents or written to every detected agent directory (#2948). During preset install, Spec Kit registers command files for the preset being installed against the currently active integration; post-install and post-removal reconciliation then recomputes and writes the effective command content for affected command names based on the active stack. A non-active installed integration does not receive these command files until it becomes the default — `specify integration use <key>` (or `switch <key>`) rescaffolds enabled presets for the newly active integration. Agents do not re-resolve the stack each time they run a command.
 
 By default, files use a **replace** strategy: the first match in the priority stack wins and is used entirely. Templates and commands can also use composition strategies: **prepend** places preset content before lower-priority content, **append** places it after lower-priority content, and **wrap** replaces `{CORE_TEMPLATE}` with lower-priority content. Scripts support **replace** and **wrap**; script wrappers use `$CORE_SCRIPT` as the placeholder.
 

src/specify_cli/_init_options.py

@@ -3,12 +3,22 @@
 import json
 from collections.abc import Mapping
 from pathlib import Path
-from typing import Any
+from typing import Any, Union
 
 
 INIT_OPTIONS_FILE = ".specify/init-options.json"
 
 
+class _MissingInitOptionsFile:
+    """Sentinel: init-options.json does not exist at all (legacy layout)."""
+
+    def __repr__(self) -> str:  # pragma: no cover - debug aid only
+        return "MISSING_INIT_OPTIONS_FILE"
+
+
+MISSING_INIT_OPTIONS_FILE = _MissingInitOptionsFile()
+
+
 def save_init_options(project_path: Path, options: dict[str, Any]) -> None:
     """Persist the CLI options used during ``specify init``."""
     dest = project_path / INIT_OPTIONS_FILE
@@ -34,3 +44,35 @@ def load_init_options(project_path: Path) -> dict[str, Any]:
 def is_ai_skills_enabled(opts: Mapping[str, Any] | None) -> bool:
     """Return True only when init options explicitly enable AI skills."""
     return isinstance(opts, Mapping) and opts.get("ai_skills") is True
+
+
+def resolve_active_agent_for_registration(
+    project_path: Path,
+) -> Union[str, None, _MissingInitOptionsFile]:
+    """Resolve the active integration key for active-only registration (#2948).
+
+    ``load_init_options`` collapses "no file", "unreadable/malformed file",
+    and "valid file with no recorded active agent" into the same ``{}``
+    result, which previously made corrupted-but-present init-options behave
+    like a legacy pre-init-options project and fall back to registering
+    every detected agent. This helper distinguishes those cases explicitly:
+
+    - Returns :data:`MISSING_INIT_OPTIONS_FILE` when init-options.json does
+      not exist at all (pre-init-options layout or direct library use).
+      Callers should fall back to detection-based registration for all
+      agents, matching the original pre-#2948 behavior for such projects.
+    - Returns ``None`` when init-options.json exists but could not provide a
+      valid non-empty string active agent (malformed/unreadable JSON,
+      non-object payload, or a non-string/empty ``ai`` value). Callers must
+      fail closed (register nothing) rather than treat this like "no file"
+      or pass a non-string key into agent-config lookups.
+    - Returns the active agent key (a non-empty string) otherwise.
+    """
+    path = project_path / INIT_OPTIONS_FILE
+    if not path.exists():
+        return MISSING_INIT_OPTIONS_FILE
+
+    active_agent = load_init_options(project_path).get("ai")
+    if isinstance(active_agent, str) and active_agent:
+        return active_agent
+    return None

src/specify_cli/agents.py

@@ -932,6 +932,7 @@ def register_commands_for_all_agents(
         link_outputs: bool = False,
         create_missing_active_skills_dir: bool = False,
         extension_id: Optional[str] = None,
+        only_agent: Optional[str] = None,
     ) -> Dict[str, List[str]]:
         """Register commands for all detected agents in the project.
 
@@ -949,6 +950,8 @@ def register_commands_for_all_agents(
                 skills directory) and is skipped when safe resolution or
                 creation fails.
             extension_id: Extension id when rendering extension-owned commands.
+            only_agent: If set, restrict registration to this single agent
+                while keeping all detection and recovery safeguards (#2948).
 
         Returns:
             Dictionary mapping agent names to list of registered commands
@@ -972,6 +975,8 @@ def register_commands_for_all_agents(
                 )
         active_created_skills_dir: Optional[Path] = None
         for agent_name, agent_config in self.AGENT_CONFIGS.items():
+            if only_agent is not None and agent_name != only_agent:
+                continue
             active_skills_output = (
                 agent_name == active_skills_agent
                 and agent_config.get("extension") == "/SKILL.md"
@@ -1077,6 +1082,7 @@ def register_commands_for_non_skill_agents(
         context_note: Optional[str] = None,
         link_outputs: bool = False,
         extension_id: Optional[str] = None,
+        only_agent: Optional[str] = None,
     ) -> Dict[str, List[str]]:
         """Register commands for all non-skill agents in the project.
 
@@ -1093,13 +1099,18 @@ def register_commands_for_non_skill_agents(
             link_outputs: If True, create dev-mode symlinks for rendered
                 command files when supported by the OS.
             extension_id: Extension id when rendering extension-owned commands.
+            only_agent: If set, restrict registration to this single agent
+                (#2948). An agent name that matches no configured agent
+                (e.g. an empty string) yields no registrations at all.
 
         Returns:
             Dictionary mapping agent names to list of registered commands
         """
         results = {}
         self._ensure_configs()
         for agent_name, agent_config in self.AGENT_CONFIGS.items():
+            if only_agent is not None and agent_name != only_agent:
+                continue
             if agent_config.get("extension") == "/SKILL.md":
                 continue
             detect_dir_str = agent_config.get("detect_dir")