test(client): pin _handle_chat None handler result → empty text

3 tests over the single-shot else branch: sync handler with no return,
async handler returning None, and an int-return guard so the fix
doesn't over-narrow the else path (only None is coerced; ints/floats/
lists keep the existing `str(result)` behavior). Mutation-verified —
reverting the fix fails both None cases and the guard still passes.

Author: Zawwarsami16

tests/test_handle_chat_none_result.py

@@ -0,0 +1,76 @@
+"""Regression: a chat_handler that forgets ``return`` (returns None from
+falling off the end of the function body) shipped the literal three-character
+string ``"None"`` as the assistant reply text — the single-shot else branch
+called ``str(result)`` on the None value.
+
+This is a common publisher-side mistake: ``def handler(msgs, opts): print(msgs)``
+runs cleanly, returns None. Before the fix the caller saw ``{"text": "None"}``
+on the wire; after the fix an empty response goes out, matching the JS port's
+``String(awaited ?? '')`` behavior.
+"""
+
+import json
+
+import pytest
+
+from zhub.client import _handle_chat
+from zhub.protocol import Envelope
+
+
+class _FakeWS:
+    def __init__(self) -> None:
+        self.sent: list[dict] = []
+
+    async def send(self, text: str) -> None:
+        self.sent.append(json.loads(text))
+
+
+class _Pub:
+    def __init__(self, handler) -> None:
+        self.chat_handler = handler
+
+
+@pytest.mark.asyncio
+async def test_sync_handler_returning_none_emits_empty_text():
+    def handler(messages, options):
+        # Common mistake: forgot the return statement. Body runs, function
+        # falls off the end, returns None.
+        pass
+
+    ws = _FakeWS()
+    env = Envelope(type="chat-request", request_id="r1", payload={"messages": []})
+    await _handle_chat(_Pub(handler), ws, env)
+
+    assert len(ws.sent) == 1
+    payload = ws.sent[0]["payload"]
+    assert payload["text"] == ""  # pre-fix: "None"
+    assert payload["finish_reason"] == "stop"
+
+
+@pytest.mark.asyncio
+async def test_async_handler_returning_none_emits_empty_text():
+    async def handler(messages, options):
+        return None
+
+    ws = _FakeWS()
+    env = Envelope(type="chat-request", request_id="r2", payload={"messages": []})
+    await _handle_chat(_Pub(handler), ws, env)
+
+    assert ws.sent[-1]["payload"]["text"] == ""
+
+
+@pytest.mark.asyncio
+async def test_int_result_still_stringified():
+    """Guard: the fix only special-cases None. A handler returning a non-None
+    non-str non-dict value (int, float, list …) is still stringified — this
+    keeps existing behavior for the two-year-stable else branch, and only
+    the ``str(None) == 'None'`` embarrassment is corrected."""
+
+    def handler(messages, options):
+        return 42
+
+    ws = _FakeWS()
+    env = Envelope(type="chat-request", request_id="r3", payload={"messages": []})
+    await _handle_chat(_Pub(handler), ws, env)
+
+    assert ws.sent[-1]["payload"]["text"] == "42"