fix: send snippet modification dates with a UTC offset

src/php/Admin/Menus/Manage/Manage_Menu_Assets.php

@@ -111,6 +111,9 @@ public function enqueue( array $script_dependencies, array $style_dependencies )
 				function ( Snippet $snippet ) {
 					$fields = $snippet->get_fields();
 					$fields['code'] = '';
+					// Match the REST response: a UTC value with no offset is read
+					// as local time by the browser.
+					$fields['modified'] = $snippet->modified_iso;
 					return $fields;
 				},
 				get_snippets()

src/php/Model/Snippet.php

@@ -463,6 +463,24 @@ protected function get_modified_timestamp(): int {
 		return $datetime ? $datetime->getTimestamp() : 0;
 	}
 
+	/**
+	 * Retrieve the modification date as an ISO 8601 string, including the UTC
+	 * offset.
+	 *
+	 * `$modified` is stored as 'Y-m-d H:i:s' in UTC, which carries no offset, so
+	 * anything parsing it — a browser, in particular — is free to read it as
+	 * local time and land the snippet hours away from when it was really saved.
+	 * This is the form to hand to clients.
+	 *
+	 * @return string|null ISO 8601 date, or null if no modification date is set.
+	 * @noinspection PhpUnused
+	 */
+	protected function get_modified_iso(): ?string {
+		$timestamp = $this->get_modified_timestamp();
+
+		return $timestamp ? gmdate( 'c', $timestamp ) : null;
+	}
+
 	/**
 	 * Retrieve the modification time in the local timezone.
 	 *

src/php/REST_API/Snippets/Snippets_REST_Controller.php

@@ -826,6 +826,10 @@ public function prepare_item_for_response( $item, $request ) {
 			$response[ $property ] = $item->$property;
 		}
 
+		// The schema declares this as a date-time, so send one: the stored value
+		// is UTC without an offset, which clients read as local time.
+		$response['modified'] = $item->modified_iso;
+
 		return rest_ensure_response( $response );
 	}
 

tests/unit/Model/Snippet_Test.php

@@ -30,4 +30,40 @@ public function test_description_round_trips_without_sanitization(): void {
 
 		$this->assertSame( $description, $snippet->desc );
 	}
+
+	/**
+	 * The modification date is exposed to clients with an explicit UTC offset.
+	 *
+	 * Stored as 'Y-m-d H:i:s' in UTC, the raw value carries no offset, so a
+	 * browser reads it as local time and shows a snippet saved moments ago as
+	 * hours into the future on any site behind UTC.
+	 *
+	 * @return void
+	 */
+	public function test_modified_is_exposed_as_iso_8601_utc(): void {
+		$snippet = new Snippet(
+            [
+				'name' => 'Timezone',
+				'modified' => '2026-08-27 07:35:20',
+			]
+        );
+
+		$this->assertSame( '2026-08-27T07:35:20+00:00', $snippet->modified_iso );
+		$this->assertNotSame(
+			$snippet->modified,
+			$snippet->modified_iso,
+			'the stored value has no offset, so it must not be handed to clients as-is'
+		);
+	}
+
+	/**
+	 * A snippet with no modification date exposes null rather than an epoch date.
+	 *
+	 * @return void
+	 */
+	public function test_modified_iso_is_null_when_unset(): void {
+		$snippet = new Snippet( [ 'name' => 'Never modified' ] );
+
+		$this->assertNull( $snippet->modified_iso );
+	}
 }