Require --context=admin for admin URL profiling, add error and test

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>

Author: Copilot

features/profile-stage.feature

@@ -176,7 +176,7 @@ Feature: Profile the template render stage
   Scenario: Admin URL runs as a backend request and skips frontend stages
     Given a WP install
 
-    When I run `wp profile stage --url=example.com/wp-admin/ --fields=stage`
+    When I run `wp profile stage --url=example.com/wp-admin/ --context=admin --fields=stage`
     Then STDOUT should be a table containing rows:
       | stage     |
       | bootstrap |
@@ -189,3 +189,14 @@ Feature: Profile the template render stage
       template
       """
     And STDERR should be empty
+
+  @require-wp-4.0
+  Scenario: Admin URL without --context=admin emits an error
+    Given a WP install
+
+    When I try `wp profile stage --url=example.com/wp-admin/ --fields=stage`
+    Then STDERR should contain:
+      """
+      Profiling an admin URL requires --context=admin.
+      """
+    And the return code should be 1

src/Profiler.php

@@ -82,6 +82,10 @@ public function run() {
 		$url                    = WP_CLI::get_runner()->config['url'];
 		$this->is_admin_request = ! empty( $url ) && (bool) preg_match( '#/wp-admin(/|$)#i', $url );
 
+		if ( $this->is_admin_request && 'admin' !== WP_CLI::get_runner()->config['context'] ) {
+			WP_CLI::error( 'Profiling an admin URL requires --context=admin.' );
+		}
+
 		WP_CLI::add_wp_hook(
 			'muplugins_loaded',
 			function () {