fix: return the created template from appliance install

POST /appliances/{id}/install replied 204 with an empty body, so the MCP
appliance_install tool crashed with 'Expecting value: line 1 column 1'
while the template had actually been created. The route now returns the
created template (201, response_model=schemas.Template), _create_template
propagates it, and the MCP handler parses the body defensively so an
empty reply degrades to a plain success message.

gns3server/agent/mcp/__init__.py

@@ -1376,7 +1376,7 @@ async def appliance_install(
     appliance_id: Annotated[str, Field(description="UUID of the appliance to install")],
     version: Annotated[str | None, Field(description="Version to install (e.g. '2.7.0.356'). Required if the appliance has multiple versions. Use appliance_get to see available versions.")] = None,
 ) -> list[dict[str, Any]]:
-    """Create a template from a GNS3 appliance definition.
+    """Create a template from a GNS3 appliance definition and return the created template.
 
     NOTE: This does NOT download images. Images must be placed in the
     GNS3 images directory (e.g. ~/GNS3/images/) beforehand.

gns3server/agent/mcp/appliances.py

@@ -85,5 +85,13 @@ def install_appliance_handler(params: dict[str, Any], gns3_ctx: dict[str, Any])
     version = params.get("version")
     if version:
         request_params["version"] = version
-    result = conn.http_call("post", url, params=request_params).json()
-    return {"message": f"Appliance {appliance_id} installation requested", "result": result}
+    response = conn.http_call("post", url, params=request_params)
+    result = {"message": f"Appliance {appliance_id} installed"}
+    if response.content:
+        # the install endpoint returns the created template (201); tolerate an
+        # empty body in case an older server still replies with 204
+        template = response.json()
+        result["template"] = {
+            k: template[k] for k in ("template_id", "name", "version", "template_type") if k in template
+        }
+    return result

gns3server/api/routes/controller/appliances.py

@@ -122,7 +122,8 @@ def add_appliance_version(appliance_id: UUID, appliance_version: Union[schemas.A
 
 @router.post(
     "/{appliance_id}/install",
-    status_code=status.HTTP_204_NO_CONTENT,
+    response_model=schemas.Template,
+    status_code=status.HTTP_201_CREATED,
     dependencies=[Depends(has_privilege("Appliance.Allocate"))]
 )
 async def install_appliance(
@@ -132,15 +133,15 @@ async def install_appliance(
         templates_repo: TemplatesRepository = Depends(get_repository(TemplatesRepository)),
         current_user: schemas.User = Depends(get_current_active_user),
         rbac_repo: RbacRepository = Depends(get_repository(RbacRepository))
-) -> None:
+) -> schemas.Template:
     """
-    Install an appliance.
+    Install an appliance and return the created template.
 
     Required privilege: Appliance.Allocate
     """
 
     controller = Controller.instance()
-    await controller.appliance_manager.install_appliance(
+    return await controller.appliance_manager.install_appliance(
         appliance_id,
         version,
         images_repo,

gns3server/controller/appliance_manager.py

@@ -204,9 +204,9 @@ class ApplianceManager:
                                 else:
                                     raise ControllerError(f"Could not find '{appliance_file}'")
 
-    async def _create_template(self, template_data, templates_repo, rbac_repo, current_user):
+    async def _create_template(self, template_data, templates_repo, rbac_repo, current_user) -> dict:
         """
-        Create a new template
+        Create a new template and return it as a dict.
         """
 
         try:
@@ -217,6 +217,7 @@ class ApplianceManager:
         #template_id = template.get("template_id")
         #await rbac_repo.add_permission_to_user_with_path(current_user.user_id, f"/templates/{template_id}/*")
         log.info(f"Template '{template.get('name')}' has been created")
+        return template
 
     async def _appliance_to_template(self, appliance: Appliance, version: str = None) -> dict:
         """