From 716eb0d09613f4b55a20db2cdc8aadab69a23448 Mon Sep 17 00:00:00 2001
From: Daniel Imfeld <daniel@imfeld.dev>
Date: Fri, 17 Apr 2026 16:21:52 -1000
Subject: [PATCH] Fix plain-text language attachment detection in diffs

---
 .../languages/areLanguagesAttached.ts         |  3 +++
 .../diffs/test/areLanguagesAttached.test.ts   | 22 +++++++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 packages/diffs/test/areLanguagesAttached.test.ts

diff --git a/packages/diffs/src/highlighter/languages/areLanguagesAttached.ts b/packages/diffs/src/highlighter/languages/areLanguagesAttached.ts
index defcea51b..34c614b08 100644
--- a/packages/diffs/src/highlighter/languages/areLanguagesAttached.ts
+++ b/packages/diffs/src/highlighter/languages/areLanguagesAttached.ts
@@ -5,6 +5,9 @@ export function areLanguagesAttached(
   languages: SupportedLanguages | SupportedLanguages[]
 ): boolean {
   for (const language of Array.isArray(languages) ? languages : [languages]) {
+    if (language === 'text' || language === 'ansi') {
+      continue;
+    }
     if (!AttachedLanguages.has(language)) {
       return false;
     }
diff --git a/packages/diffs/test/areLanguagesAttached.test.ts b/packages/diffs/test/areLanguagesAttached.test.ts
new file mode 100644
index 000000000..203c46334
--- /dev/null
+++ b/packages/diffs/test/areLanguagesAttached.test.ts
@@ -0,0 +1,22 @@
+import { describe, expect, test } from 'bun:test';
+
+import { areLanguagesAttached } from '../src/highlighter/languages/areLanguagesAttached';
+import { AttachedLanguages } from '../src/highlighter/languages/constants';
+
+describe('areLanguagesAttached', () => {
+  test('treats builtin text-like languages as already attached', () => {
+    AttachedLanguages.clear();
+
+    expect(areLanguagesAttached('text')).toBe(true);
+    expect(areLanguagesAttached('ansi')).toBe(true);
+  });
+
+  test('still requires explicit attachment for non-builtin languages', () => {
+    AttachedLanguages.clear();
+
+    expect(areLanguagesAttached('typescript')).toBe(false);
+
+    AttachedLanguages.add('typescript');
+    expect(areLanguagesAttached('typescript')).toBe(true);
+  });
+});