fix(chat): reject empty Claude Code responses

loopx/chat_providers.py

@@ -240,7 +240,18 @@ def start_turn(self, message: str, event_sink: EventSink) -> dict[str, Any]:
         finally:
             with self.lock:
                 self.current_process = None
-        raw_response = "".join(parts) or result_text
+        streamed_response = "".join(parts)
+        raw_response = streamed_response if streamed_response.strip() else result_text
+        if not raw_response.strip():
+            summary = "Claude Code completed without returning an answer."
+            raise CodexChatAgentError(
+                summary,
+                error_code="provider_empty_response",
+                gate=_host_tool_gate(
+                    summary,
+                    "Retry this session or select another healthy Agent endpoint.",
+                ),
+            )
         if not parts and result_text:
             visible = display_filter.feed(result_text)
             if visible:

tests/test_chat_agent.py

@@ -6,6 +6,7 @@
 from pathlib import Path
 
 import loopx.chat_agent as chat_agent
+import loopx.chat_providers as chat_providers
 import loopx.chat_runtime as chat_runtime
 import pytest
 
@@ -35,6 +36,92 @@ def kill(self) -> None:
         self.returncode = -1
 
 
+class _FakeClaudeProcess:
+    def __init__(self, stdout: str) -> None:
+        self.stdout = io.StringIO(stdout)
+
+    def wait(self) -> int:
+        return 0
+
+
+@pytest.mark.parametrize(
+    "stdout",
+    [
+        "",
+        "not-json\n[]\n",
+        json.dumps({"type": "result", "result": ""}) + "\n",
+    ],
+)
+def test_claude_code_rejects_successful_process_without_a_response(
+    monkeypatch: pytest.MonkeyPatch,
+    tmp_path: Path,
+    stdout: str,
+) -> None:
+    monkeypatch.setattr(
+        chat_providers.subprocess,
+        "Popen",
+        lambda *args, **kwargs: _FakeClaudeProcess(stdout),
+    )
+    adapter = chat_providers.ClaudeCodeAdapter(
+        claude_bin="claude",
+        work_dir=tmp_path,
+        session_id="session-fixture",
+    )
+    events: list[tuple[str, dict[str, object]]] = []
+
+    with pytest.raises(chat_agent.CodexChatAgentError) as caught:
+        adapter.start_turn(
+            "Reply briefly.",
+            lambda kind, payload: events.append((kind, payload)),
+        )
+
+    assert caught.value.error_code == "provider_empty_response"
+    assert not any(kind == "answer.final" for kind, _ in events)
+    assert adapter.resumed is False
+
+
+@pytest.mark.parametrize(
+    "payload",
+    [
+        {"type": "result", "result": "Completed."},
+        {
+            "type": "stream_event",
+            "event": {
+                "type": "content_block_delta",
+                "delta": {"type": "text_delta", "text": "Completed."},
+            },
+        },
+    ],
+)
+def test_claude_code_accepts_a_nonempty_response_event(
+    monkeypatch: pytest.MonkeyPatch,
+    tmp_path: Path,
+    payload: dict[str, object],
+) -> None:
+    stdout = json.dumps({**payload, "session_id": "upstream-session"})
+    monkeypatch.setattr(
+        chat_providers.subprocess,
+        "Popen",
+        lambda *args, **kwargs: _FakeClaudeProcess(stdout + "\n"),
+    )
+    adapter = chat_providers.ClaudeCodeAdapter(
+        claude_bin="claude",
+        work_dir=tmp_path,
+        session_id="session-fixture",
+    )
+    events: list[tuple[str, dict[str, object]]] = []
+
+    response = adapter.start_turn(
+        "Reply briefly.",
+        lambda kind, payload: events.append((kind, payload)),
+    )
+
+    assert response["message"] == "Completed."
+    assert sum(kind == "answer.final" for kind, _ in events) == 1
+    assert adapter.session_id == "upstream-session"
+    assert adapter.resumed is True
+
+
 def test_codex_chat_app_server_stdio_uses_utf8(
     monkeypatch: pytest.MonkeyPatch,
     tmp_path: Path,