fix(tui): cancel silent streams promptly

Move chat streaming onto a cancellable async task so Ctrl+C interrupts a pending socket read on macOS instead of waiting for the 120-second read timeout. Add a headless silent-stream regression that verifies prompt recovery and a successful next message.

tests/test_tui.py

@@ -154,15 +154,15 @@ def test_inflight_tool_denial_uses_original_conversation_id(monkeypatch):
     class _StreamResponse:
         status_code = 200
 
-        def __enter__(self):
+        async def __aenter__(self):
             return self
 
-        def __exit__(self, *args):
+        async def __aexit__(self, *args):
             return None
 
-        def iter_lines(self):
+        async def aiter_lines(self):
             stream_started.set()
-            release_stream.wait(timeout=2)
+            await asyncio.to_thread(release_stream.wait, 2)
             yield "event: tool_request"
             yield 'data: {"token":"secret","actions":[{"name":"run_snippet"}]}'
             yield ""
@@ -173,17 +173,20 @@ def test_inflight_tool_denial_uses_original_conversation_id(monkeypatch):
         def __init__(self, **kwargs):
             pass
 
+        async def __aenter__(self):
+            return self
+
+        async def __aexit__(self, *args):
+            return None
+
         def stream(self, *args, **kwargs):
             return _StreamResponse()
 
-        def close(self):
-            return None
-
     def _capture_denial(*, conversation_id, **kwargs):
         denied_for.append(conversation_id)
         return ["run_snippet"]
 
-    monkeypatch.setattr(tui_app.httpx, "Client", _StreamClient)
+    monkeypatch.setattr(tui_app.httpx, "AsyncClient", _StreamClient)
     monkeypatch.setattr(tui_app, "_deny_tool_request", _capture_denial)
     app = tui_app.NexusTUI.build_app(api_url="http://127.0.0.1:9")
 
@@ -205,5 +208,78 @@ def test_inflight_tool_denial_uses_original_conversation_id(monkeypatch):
     asyncio.run(_run())
 
 
+def test_interrupt_cancels_silent_stream_and_accepts_next_message(monkeypatch):
+    pytest.importorskip("textual")
+    import nexusos_cli.tui_app as tui_app
+
+    first_stream_started = threading.Event()
+
+    class _StreamResponse:
+        status_code = 200
+
+        def __init__(self, call_number):
+            self.call_number = call_number
+
+        async def __aenter__(self):
+            return self
+
+        async def __aexit__(self, *args):
+            return None
+
+        async def aiter_lines(self):
+            if self.call_number == 1:
+                first_stream_started.set()
+                await asyncio.Event().wait()
+            yield "data: \"READY\""
+            yield ""
+            yield "event: done"
+            yield "data: {}"
+
+    class _StreamClient:
+        calls = 0
+
+        def __init__(self, **kwargs):
+            pass
+
+        async def __aenter__(self):
+            return self
+
+        async def __aexit__(self, *args):
+            return None
+
+        def stream(self, *args, **kwargs):
+            type(self).calls += 1
+            return _StreamResponse(type(self).calls)
+
+    monkeypatch.setattr(tui_app.httpx, "AsyncClient", _StreamClient)
+    app = tui_app.NexusTUI.build_app(api_url="http://127.0.0.1:9")
+
+    async def _wait_until_idle():
+        for _ in range(100):
+            if not app._busy:
+                return
+            await asyncio.sleep(0.01)
+        pytest.fail("stream did not become idle within one second")
+
+    async def _run():
+        async with app.run_test():
+            app._start_chat("first")
+            assert await asyncio.to_thread(first_stream_started.wait, 2)
+            app.action_interrupt()
+            await _wait_until_idle()
+
+            log = app.query_one("#log")
+            assert not any("ReadTimeout" in line.text for line in log.lines)
+
+            app._start_chat("second")
+            await _wait_until_idle()
+            assert app.history[-1] == {
+                "role": "assistant",
+                "content": "READY",
+            }
+
+    asyncio.run(_run())
+
+
 def test_escape_round_trip_helper():
     assert "[" in _escape("x[y]") or "\\[" in _escape("x[y]")