Fix admin resend-activation email missing hostname

In a FastAPI request, UrlBuilder's NoMatchFound fallback called
web.url_for without the popped qualified flag, and routes.url_for has
no host available in an ASGI context. The admin resend-activation
endpoint hits this path (since /user/activate is a WSGI-only
@web.expose route) and produced links like http:///user/activate?... .

Latent in the FastAPI endpoint since 72d5cceda8 ("Add mail activation
operation to api"); surfaced for users after c9b849d934 bumped
fastapi 0.135.3 -> 0.136.0.

Qualify the fallback URL with request.base_url when qualified=True.

Integration test posts to /api/users/{user_id}/send_activation_email as
admin with mock SMTP capture, then asserts the captured email body
contains a fully-qualified activation link with a non-empty host. Would
have caught the regression that produced http:///user/activate?... .

lib/galaxy/webapps/galaxy/api/__init__.py

@@ -228,10 +228,15 @@ class UrlBuilder:
                 url = f"{url}?{urlencode(query_params)}"
             return url
         except NoMatchFound:
-            # Fallback to legacy url_for
+            # Fallback to legacy WSGI url_for for routes not registered with FastAPI
             if query_params:
                 path_params.update(query_params)
-            return web.url_for(name, **path_params)
+            url = web.url_for(name, **path_params)
+            if qualified and not url.startswith(("http://", "https://")):
+                # routes.url_for has no thread-local request_config in an ASGI
+                # request, so qualify the URL using the FastAPI request base_url.
+                url = str(self.request.base_url).rstrip("/") + url
+            return url
 
     def _url_path_for(self, name: str, **path_params) -> str:
         """O(1) route lookup using the app's pre-built name index.

test/integration/test_users.py

@@ -1,3 +1,6 @@
+import json
+import os
+import re
 from typing import (
     ClassVar,
 )
@@ -91,3 +94,31 @@ class TestUnexposedUsersIntegration(UsersIntegrationCase):
     # And the current user has all fields, so no limited fields.
     expected_limited_user_keys = set()
     expected_regular_user_list_count = 1
+
+
+class TestAdminResendActivationEmail(integration_util.IntegrationTestCase):
+    email_directory: ClassVar[str]
+
+    @classmethod
+    def handle_galaxy_config_kwds(cls, config):
+        super().handle_galaxy_config_kwds(config)
+        cls.email_directory = cls._test_driver.mkdtemp()
+        config["user_activation_on"] = True
+        config["activation_grace_period"] = 3
+        config["email_from"] = "galaxy-noreply@example.com"
+        config["smtp_server"] = f"mock_emails_to_path://{cls.email_directory}/email.json"
+
+    def test_resend_activation_includes_qualified_link(self):
+        user = self._setup_user("resend-activation@test.gx")
+        response = self._post(f"users/{user['id']}/send_activation_email", admin=True)
+        self._assert_status_code_is_ok(response)
+
+        with open(os.path.join(self.email_directory, "email.json")) as f:
+            email = json.loads(f.read())
+        assert email["to"] == "resend-activation@test.gx"
+        assert email["subject"] == "Galaxy Account Activation"
+        match = re.search(r"(https?://[^/\s]+/user/activate\?[^\s]+)", email["body"])
+        assert match, f"No qualified activation link found in email body:\n{email['body']}"
+        link = match.group(1)
+        assert "activation_token=" in link
+        assert "email=" in link