test(fs-local): pin multibyte byte-length gating

packages/fs/fs-local/tests/filesystem.spec.ts

@@ -438,6 +438,18 @@ describe('writeText', () => {
     expect(outcome.after).toBe('12345678')
   })
 
+  it('gates the NEW content by UTF-8 byte length, not character count', async () => {
+    // Three CJK characters are 9 UTF-8 bytes: below an 8-byte bound by
+    // characters but at/above it by bytes, so the basis must be declined.
+    await remountWithDiffLimit(8)
+    await writeFile(join(dir, 'cjk.txt'), 'tiny')
+    const target = await fs.resolve('cjk.txt')
+    const outcome = await fs.writeText(target, '你好吗')
+    expect(outcome.operation).toBe('update')
+    expect(outcome.before).toBeNull()
+    expect(outcome.after).toBe('你好吗')
+  })
+
   it('an overwrite with BOTH sides below the whole-file bound keeps its contextual before basis', async () => {
     await remountWithDiffLimit(8)
     await writeFile(join(dir, 'small.txt'), '1234567')

packages/fs/fs-local/tests/fsio.spec.ts

@@ -367,8 +367,6 @@ describe('readTextForDiff', () => {
   })
 
   it('returns null when the opened file grows after descriptor stat', async () => {
-    // Pins the one-extra-byte EOF probe: with a buffer of exactly openedSize a
-    // grown file would read openedSize bytes and pass the consistency check.
     const file = join(dir, 'growing.txt')
     await writeFile(file, 'abcdef')
     vi.resetModules()