Don't re-generate scaled/rotated images when regenerating a specific image size

features/media-regenerate.feature

@@ -832,6 +832,43 @@ Feature: Regenerate WordPress attachments
       Success: Regenerated 1 of 1 images.
       """
 
+  @require-wp-5.3
+  Scenario: Regenerating a specific image size should not regenerate the scaled version of big images
+    Given download:
+      | path                        | url                                          |
+      | {CACHE_DIR}/large-image.jpg | http://wp-cli.org/behat-data/large-image.jpg |
+    And I run `wp option update uploads_use_yearmonth_folders 0`
+
+    When I run `wp media import {CACHE_DIR}/large-image.jpg --title="My imported attachment" --porcelain`
+    Then save STDOUT as {LARGE_ATTACHMENT_ID}
+    And the wp-content/uploads/large-image-scaled.jpg file should exist
+    And the wp-content/uploads/large-image-300x225.jpg file should exist
+
+    # Save a checksum of the scaled image before any regeneration.
+    When I run `md5sum wp-content/uploads/large-image-scaled.jpg`
+    Then save STDOUT as {SCALED_CHECKSUM}
+
+    # Add a filter that would produce drastically different results if the scaled image were regenerated.
+    Given a wp-content/mu-plugins/media-settings.php file:
+      """
+      <?php
+      add_filter( 'jpeg_quality', function() { return 1; } );
+      """
+
+    # Regenerate only the medium size - scaled image should not be touched.
+    When I run `wp media regenerate {LARGE_ATTACHMENT_ID} --image_size=medium --yes`
+    Then STDOUT should contain:
+      """
+      Regenerated "medium" thumbnail for "My imported attachment"
+      """
+
+    # Verify the scaled image was NOT regenerated (checksum should be unchanged).
+    When I run `md5sum wp-content/uploads/large-image-scaled.jpg`
+    Then STDOUT should be:
+      """
+      {SCALED_CHECKSUM}
+      """
+
   @require-wp-4.7.3 @require-extension-imagick
   Scenario: Regenerate a specific image size for a PDF attachment
     Given download:

src/Media_Command.php

@@ -665,10 +665,21 @@ private function process_regeneration( $id, $skip_delete, $only_missing, $delete
 			++$successes;
 			return;
 		}
-
 		$site_icon_filter = $this->add_site_icon_filter( $id );
 
-		$metadata = wp_generate_attachment_metadata( $id, $fullsizepath );
+		// When regenerating a specific image size, use the file that WordPress normally
+		// serves (the scaled version for big images), not the original pre-scaled file.
+		// This prevents wp_generate_attachment_metadata() from re-creating the scaled
+		// version or auto-rotating the original during specific-size regeneration.
+		$generate_file = $fullsizepath;
+		if ( $image_size && ! $is_pdf ) {
+			$wp_attached_file = \get_attached_file( $id );
+			if ( $wp_attached_file && file_exists( $wp_attached_file ) ) {
+				$generate_file = $wp_attached_file;
+			}
+		}
+
+		$metadata = wp_generate_attachment_metadata( $id, $generate_file );
 
 		if ( $site_icon_filter ) {
 			remove_filter( 'intermediate_image_sizes_advanced', $site_icon_filter );