From 9828569f97925b3f14376376e4776717ff6d8792 Mon Sep 17 00:00:00 2001
From: Ramon <ramonjd@gmail.com>
Date: Tue, 1 Sep 2026 17:42:25 +1000
Subject: [PATCH 1/2] getResolvedValue: stop writing the resolved URL onto the
 given object

The resolved object can be the caller's own value or, when a ref was
just resolved, the tree's own object, which aliases the user or theme
config because mergeGlobalStyles keeps backgroundImage leaves atomic.
Writing the resolved absolute URL in place could convert a portable
theme-relative file: pointer into a hardcoded site URL in data that
gets saved. Return a copy instead.
---
 packages/global-styles-engine/CHANGELOG.md    |  4 ++++
 .../src/test/utils.test.ts                    | 23 +++++++++++++++++++
 .../global-styles-engine/src/utils/common.ts  | 16 +++++++++----
 3 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/packages/global-styles-engine/CHANGELOG.md b/packages/global-styles-engine/CHANGELOG.md
index cf7c7452955ca3..f78728ac1b19fe 100644
--- a/packages/global-styles-engine/CHANGELOG.md
+++ b/packages/global-styles-engine/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### Bug Fixes
+
+-   `getResolvedValue`: Return a copy when resolving a theme-relative (`file:./…`) URL instead of writing the resolved URL onto the given object, which could be the caller's own value or, via a `ref`, an object aliased by the user or theme config ([#XXXXX](https://github.com/WordPress/gutenberg/pull/XXXXX)).
+
 ## 1.21.0 (2026-08-26)
 
 ### Bug Fixes
diff --git a/packages/global-styles-engine/src/test/utils.test.ts b/packages/global-styles-engine/src/test/utils.test.ts
index 6969c43052821f..4e3a60ba1d4cfe 100644
--- a/packages/global-styles-engine/src/test/utils.test.ts
+++ b/packages/global-styles-engine/src/test/utils.test.ts
@@ -482,5 +482,28 @@ describe( 'editor utils', () => {
 				).toEqual( returnedValue );
 			}
 		);
+
+		it( 'returns a copy instead of writing the resolved URL onto the given value', () => {
+			const ruleValue = { url: 'file:./assets/image.jpg' };
+			expect( getResolvedValue( ruleValue, themeJson ) ).toEqual( {
+				url: 'https://wordpress.org/assets/image.jpg',
+			} );
+			expect( ruleValue.url ).toBe( 'file:./assets/image.jpg' );
+		} );
+
+		it( 'does not write the resolved URL into the tree when resolving a ref', () => {
+			const tree = JSON.parse(
+				JSON.stringify( themeJson )
+			) as GlobalStylesConfig;
+			expect(
+				getResolvedValue(
+					{ ref: 'styles.background.backgroundImage' },
+					tree
+				)
+			).toEqual( { url: 'https://wordpress.org/assets/image.jpg' } );
+			expect( tree.styles?.background?.backgroundImage ).toEqual( {
+				url: 'file:./assets/image.jpg',
+			} );
+		} );
 	} );
 } );
diff --git a/packages/global-styles-engine/src/utils/common.ts b/packages/global-styles-engine/src/utils/common.ts
index e5f5c0cfa02d27..07d80c2a2ab7bf 100644
--- a/packages/global-styles-engine/src/utils/common.ts
+++ b/packages/global-styles-engine/src/utils/common.ts
@@ -469,10 +469,18 @@ export function getResolvedValue(
 		'url' in resolvedValue &&
 		resolvedValue?.url
 	) {
-		resolvedValue.url = getResolvedThemeFilePath(
-			resolvedValue.url,
-			tree?._links?.[ 'wp:theme-file' ]
-		);
+		/*
+		 * Copy rather than write in place: `resolvedValue` is the caller's
+		 * own object or, when a `ref` was just resolved, the tree's — which
+		 * aliases the user or theme config.
+		 */
+		return {
+			...resolvedValue,
+			url: getResolvedThemeFilePath(
+				resolvedValue.url,
+				tree?._links?.[ 'wp:theme-file' ]
+			),
+		};
 	}
 
 	return resolvedValue;

From c66b760b007c33085481e1b700c05affdecfb663 Mon Sep 17 00:00:00 2001
From: Ramon <ramonjd@gmail.com>
Date: Tue, 1 Sep 2026 17:43:05 +1000
Subject: [PATCH 2/2] Fill in the changelog PR reference

---
 packages/global-styles-engine/CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/global-styles-engine/CHANGELOG.md b/packages/global-styles-engine/CHANGELOG.md
index f78728ac1b19fe..911ccaaf2fbe08 100644
--- a/packages/global-styles-engine/CHANGELOG.md
+++ b/packages/global-styles-engine/CHANGELOG.md
@@ -4,7 +4,7 @@
 
 ### Bug Fixes
 
--   `getResolvedValue`: Return a copy when resolving a theme-relative (`file:./…`) URL instead of writing the resolved URL onto the given object, which could be the caller's own value or, via a `ref`, an object aliased by the user or theme config ([#XXXXX](https://github.com/WordPress/gutenberg/pull/XXXXX)).
+-   `getResolvedValue`: Return a copy when resolving a theme-relative (`file:./…`) URL instead of writing the resolved URL onto the given object, which could be the caller's own value or, via a `ref`, an object aliased by the user or theme config ([#82278](https://github.com/WordPress/gutenberg/pull/82278)).
 
 ## 1.21.0 (2026-08-26)