test: expand command/PTY/git coverage, fix WebSocket close handling

Tests:
- tests/test_commands.py: unit coverage for Commands/AsyncCommands —
  payload construction (cwd, envs, tag, timeout), background dispatch,
  base64 response decoding, stream-event parsing, stream/connect iterators.
- tests/test_integration_advanced.py: live tests for cwd/env handling,
  long-running commands (apt-get), PTY sessions, streaming exec,
  process connect, and git workflows including cloning wrennhq/wrenn.
- test_filesystem_pty.py: PTY ping/pong reply tests.
- test_integration.py: poll for async process-registry prune in
  test_kill_process instead of asserting on a zero-delay list().

Fixes:
- commands.py / pty.py: stream(), connect() and the PTY iterators only
  caught WebSocketDisconnect. The server closes exec/process streams
  abruptly, raising WebSocketNetworkError — a sibling under
  HTTPXWSException — which crashed connect() entirely. Both are now
  caught via _WS_CLOSED so abrupt closes end iteration cleanly.
- pty.py: reply to the server keepalive ping with a pong so idle PTY
  sessions stay open.

tests/test_filesystem_pty.py

@@ -341,6 +341,39 @@ class TestPtySessionIteration:
         assert events == []
 
 
+class TestPtySessionPong:
+    def test_ping_triggers_pong(self):
+        ws = MagicMock()
+        ws.receive_text.side_effect = [
+            json.dumps({"type": "ping"}),
+            json.dumps({"type": "exit", "exit_code": 0}),
+        ]
+        session = PtySession(ws, "cl-abc")
+        events = list(session)
+        assert events[0].type == PtyEventType.ping
+        sent = [json.loads(c[0][0]) for c in ws.send_text.call_args_list]
+        assert {"type": "pong"} in sent
+
+    def test_no_pong_without_ping(self):
+        ws = MagicMock()
+        ws.receive_text.side_effect = [
+            json.dumps({"type": "output", "data": ""}),
+            json.dumps({"type": "exit", "exit_code": 0}),
+        ]
+        session = PtySession(ws, "cl-abc")
+        list(session)
+        sent = [json.loads(c[0][0]) for c in ws.send_text.call_args_list]
+        assert {"type": "pong"} not in sent
+
+    def test_send_pong_swallows_closed_ws(self):
+        import httpx_ws
+
+        ws = MagicMock()
+        ws.send_text.side_effect = httpx_ws.WebSocketNetworkError()
+        session = PtySession(ws, "cl-abc")
+        session._send_pong()  # must not raise
+
+
 class TestPtySessionContextManager:
     def test_exit_kills_and_closes(self):
         ws = MagicMock()
@@ -450,6 +483,28 @@ class TestAsyncPtySession:
         assert sent["cmd"] == "/bin/zsh"
         assert sent["cols"] == 100
 
+    @pytest.mark.asyncio
+    async def test_async_ping_triggers_pong(self):
+        ws = AsyncMock()
+        ws.receive_text.side_effect = [
+            json.dumps({"type": "ping"}),
+            json.dumps({"type": "exit", "exit_code": 0}),
+        ]
+        session = AsyncPtySession(ws, "cl-abc")
+        events = [e async for e in session]
+        assert events[0].type == PtyEventType.ping
+        sent = [json.loads(c[0][0]) for c in ws.send_text.call_args_list]
+        assert {"type": "pong"} in sent
+
+    @pytest.mark.asyncio
+    async def test_async_send_pong_swallows_closed_ws(self):
+        import httpx_ws
+
+        ws = AsyncMock()
+        ws.send_text.side_effect = httpx_ws.WebSocketNetworkError()
+        session = AsyncPtySession(ws, "cl-abc")
+        await session._send_pong()  # must not raise
+
     @pytest.mark.asyncio
     async def test_async_iteration(self):
         ws = AsyncMock()