feat(fs): append recovery remedy to guarded-mutation errors

write/edit failures with FS_STALE_VERSION or FS_NOT_OBSERVED now reach the
model with the correct recovery instruction appended (re-read / read, then
retry) while preserving the structured code and chaining the cause. The
edit-intent waterfall sits inside the same try, so the policy's
FS_NOT_OBSERVED refusal is remediated too. Re-recorded the fs-policy-reject
keyless snapshot and the bilingual README pairs.

packages/fs/tool-fs/tests/tools.spec.ts

@@ -397,12 +397,13 @@ describe('write tool', () => {
     expect(text(result)).toContain('file_path must be a non-empty string')
   })
 
-  it('propagates a backend FsError as an isError result carrying its code', async () => {
+  it('propagates a backend FsError as an isError result carrying its code and remedy', async () => {
     const { ctx, fs } = await setup()
     fs.rejectWith = new FsError('blocked', 'FS_STALE_VERSION')
     const result = await call(ctx, 'write', { file_path: 'a.txt', content: 'hi' })
     expect(result.isError).toBe(true)
     expect(result.error).toMatchObject({ info: { name: 'FsError', code: 'FS_STALE_VERSION' } })
+    expect(text(result)).toContain('re-read the file, then retry')
   })
 })