fix(files): let context panel open binaries into FilesView safely

Skip UTF-8 pre-read for known binary/image/PDF paths so the shared
editor can show preview or cannot-preview instead of failing open or
decoding binaries as text.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/ui/src/lib/contextFileOpenGuard.test.ts

@@ -0,0 +1,36 @@
+import { describe, expect, test } from 'bun:test';
+
+import type { FilesAPI } from '@/lib/api/types';
+import { validateContextFileOpen } from './contextFileOpenGuard';
+
+const filesApi = (content: string): FilesAPI => ({
+  listDirectory: async () => ({ path: '/', entries: [] }),
+  readFile: async () => ({ content, path: '/x' }),
+});
+
+describe('validateContextFileOpen', () => {
+  test('allows known binaries through without reading text', async () => {
+    const files: FilesAPI = {
+      listDirectory: async () => ({ path: '/', entries: [] }),
+      readFile: async () => {
+        throw new Error('should not read binary as text');
+      },
+    };
+
+    await expect(validateContextFileOpen(files, '/repo/docs/report.pdf')).resolves.toEqual({ ok: true });
+    await expect(validateContextFileOpen(files, '/repo/docs/report.docx')).resolves.toEqual({ ok: true });
+    await expect(validateContextFileOpen(files, '/repo/docs/pixel.png')).resolves.toEqual({ ok: true });
+    await expect(validateContextFileOpen(files, '/repo/bin/archive.zip')).resolves.toEqual({ ok: true });
+  });
+
+  test('rejects text payloads that look binary', async () => {
+    await expect(validateContextFileOpen(filesApi('%PDF-1.7\nbinary'), '/repo/mystery.bin.bak')).resolves.toEqual({
+      ok: false,
+      reason: 'binary',
+    });
+  });
+
+  test('allows ordinary text files', async () => {
+    await expect(validateContextFileOpen(filesApi('hello\nworld\n'), '/repo/notes.txt')).resolves.toEqual({ ok: true });
+  });
+});

packages/ui/src/lib/contextFileOpenGuard.ts

@@ -6,8 +6,9 @@ import { formatMessage, useI18nStore } from '@/lib/i18n/store';
 const t = (key: Parameters<typeof formatMessage>[1], params?: Parameters<typeof formatMessage>[2]) =>
   formatMessage(useI18nStore.getState().dictionary, key, params);
 import { runtimeFetch } from '@/lib/runtime-fetch';
+import { isBinaryFile, isImageFile, isPdfFile, looksLikeBinaryText } from '@/lib/toolHelpers';
 
-export type ContextFileOpenFailureReason = 'too-large' | 'missing' | 'unreadable';
+export type ContextFileOpenFailureReason = 'too-large' | 'missing' | 'unreadable' | 'binary';
 
 export type ContextFileOpenValidationResult =
   | { ok: true }
@@ -49,9 +50,21 @@ const readFileContent = async (files: FilesAPI, path: string): Promise<string> =
   return response.text();
 };
 
+/**
+ * Validate whether a context-panel click may open a path in the shared file editor.
+ * Previewable/non-text binaries are allowed through so FilesView can show image/PDF
+ * preview or the cannot-preview empty state — never by decoding them as editable text here.
+ */
 export const validateContextFileOpen = async (files: FilesAPI, path: string): Promise<ContextFileOpenValidationResult> => {
+  if (isBinaryFile(path) || isPdfFile(path) || isImageFile(path)) {
+    return { ok: true };
+  }
+
   try {
     const content = await readFileContent(files, path);
+    if (looksLikeBinaryText(content)) {
+      return { ok: false, reason: 'binary' };
+    }
     const lineCount = countLinesWithLimit(content, MAX_OPEN_FILE_LINES);
     if (lineCount > MAX_OPEN_FILE_LINES) {
       return { ok: false, reason: 'too-large' };
@@ -73,5 +86,9 @@ export const getContextFileOpenFailureMessage = (reason: ContextFileOpenFailureR
     return t('contextFileOpen.failure.missing');
   }
 
+  if (reason === 'binary') {
+    return t('filesView.editor.cannotPreviewBinary');
+  }
+
   return t('contextFileOpen.failure.unreadable');
 };