fix(code-runtime-python): write dispatch frames through def-time bound primitives

The review's remaining functional item: send_sync's body resolves
_encode_json_plain (module global) and self.write_encoded (class attribute) at
call time, so a program rebinding either before the first binding call could
turn a legitimate call into an exception. dispatch now writes the call frame
through def-time bound write_encoded+_encode_json_plain, and the log sink goes
through the bound send; the dispatch rebind test also rebinds those two names
(verified fail-before by reverting to send_sync). The annotation test title
matches its assertion direction, and the note (en + zh) registers the
error-class constructor, dispatch primitives, and dont_inherit mechanisms.
Pairing re-recorded.

packages/code-runtime/code-runtime-python/py/bootstrap.py

@@ -946,6 +946,13 @@ async def _run(channel: ProtocolChannel) -> None:
     _lossless_json_violation_cls = _lossless_json_violation
     _get_event_loop_cls = asyncio.get_event_loop
     _send_sync_cls = channel.send_sync
+    # The frame WRITE primitives are bound too: send_sync's body resolves
+    # `_encode_json_plain` (module global) and `self.write_encoded` (class
+    # attribute) at call time, so a program rebinding either before the first
+    # binding call could turn a legitimate call into an exception. dispatch
+    # writes through these directly, and the log sink through the bound send.
+    _write_encoded_cls = channel.write_encoded
+    _encode_plain_cls = _encode_json_plain
     # 1. Boot handshake.
     boot = channel.read_frame()
     if boot is None or boot.get("type") != "boot":
@@ -1025,7 +1032,7 @@ async def _run(channel: ProtocolChannel) -> None:
 
     logs = LogBuffer(
         int(boot["maxLogBytes"]),
-        sink=lambda text, truncated=False: channel.send_sync(
+        sink=lambda text, truncated=False: _send_sync_cls(
             {"type": "log", "text": text, **({"truncated": True} if truncated else {})}
         ),
     )
@@ -1092,14 +1099,16 @@ async def _run(channel: ProtocolChannel) -> None:
             fut: asyncio.Future[Any] = loop.create_future()
             pending[call_id] = (loop, fut)
             try:
-                _send_sync_cls(
-                    {
-                        "type": "call",
-                        "id": call_id,
-                        "global": global_name,
-                        "name": name,
-                        "args": args,
-                    }
+                _write_encoded_cls(
+                    _encode_plain_cls(
+                        {
+                            "type": "call",
+                            "id": call_id,
+                            "global": global_name,
+                            "name": name,
+                            "args": args,
+                        }
+                    )
                 )
             except (TypeError, ValueError) as exc:
                 pending.pop(call_id, None)

packages/code-runtime/code-runtime-python/tests/runtime.spec.ts

@@ -711,6 +711,8 @@ describe('PythonCodeRuntime — programs and bindings', () => {
         '__main__._lossless_json_violation = boom',
         '__main__.asyncio = boom',
         '__main__.ProtocolChannel.send_sync = boom',
+        '__main__._encode_json_plain = boom',
+        '__main__.ProtocolChannel.write_encoded = boom',
         'first = await tools.echo({"n": 1})',
         'return first',
       ].join('\n'),
@@ -2745,7 +2747,7 @@ describe('PythonCodeRuntime — budgets, termination, disposal', () => {
     expect(result.value).toBe("read: ''")
   }, 15_000)
 
-  it('keeps runtime type annotations unevaluated-as-strings when the program reads them', async () => {
+  it('keeps runtime type annotations as live classes, not PEP 563 strings, when the program reads them', async () => {
     // bootstrap.py imports `from __future__ import annotations`; without
     // dont_inherit=True on compile(), that PEP 563 flag leaks into the program's
     // compiled code and stringifies its type annotations, changing the semantics