fix(virtual-env): fix Docker stdout/stderr demuxing and exit code parsing

- Add _DockerDemuxer to properly separate stdout/stderr from multiplexed stream
- Fix binary header garbage in Docker exec output (tty=False 8-byte header)
- Fix LocalVirtualEnvironment.get_command_status() to use os.WEXITSTATUS()
- Update tests to use Transport API instead of raw file descriptors

api/tests/unit_tests/core/virtual_environment/test_local_without_isolation.py

@@ -1,31 +1,27 @@
-import os
 from io import BytesIO
 from pathlib import Path
 
 import pytest
 
+from core.virtual_environment.channel.exec import TransportEOFError
+from core.virtual_environment.channel.transport import TransportReadCloser
 from core.virtual_environment.providers import local_without_isolation
 from core.virtual_environment.providers.local_without_isolation import LocalVirtualEnvironment
 
 
-def _read_all(fd: int) -> bytes:
+def _drain_transport(transport: TransportReadCloser) -> bytes:
     chunks: list[bytes] = []
-    while True:
-        data = os.read(fd, 4096)
-        if not data:
-            break
-        chunks.append(data)
+    try:
+        while True:
+            data = transport.read(4096)
+            if not data:
+                break
+            chunks.append(data)
+    except TransportEOFError:
+        pass
     return b"".join(chunks)
 
 
-def _close_fds(*fds: int) -> None:
-    for fd in fds:
-        try:
-            os.close(fd)
-        except OSError:
-            pass
-
-
 @pytest.fixture
 def local_env(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> LocalVirtualEnvironment:
     monkeypatch.setattr(local_without_isolation, "machine", lambda: "x86_64")
@@ -35,7 +31,7 @@ def local_env(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> LocalVirtualEn
 def test_construct_environment_creates_working_path(local_env: LocalVirtualEnvironment):
     working_path = local_env.get_working_path()
     assert local_env.metadata.id
-    assert os.path.isdir(working_path)
+    assert Path(working_path).is_dir()
 
 
 def test_upload_download_roundtrip(local_env: LocalVirtualEnvironment):
@@ -54,7 +50,7 @@ def test_list_files_respects_limit(local_env: LocalVirtualEnvironment):
     all_files = local_env.list_files("", limit=10)
     all_paths = {state.path for state in all_files}
 
-    assert os.path.join("dir", "file_a.txt") in all_paths
+    assert "dir/file_a.txt" in all_paths or "dir\\file_a.txt" in all_paths
     assert "file_b.txt" in all_paths
 
     limited_files = local_env.list_files("", limit=1)
@@ -66,16 +62,15 @@ def test_execute_command_uses_working_directory(local_env: LocalVirtualEnvironme
     connection = local_env.establish_connection()
     command = ["/bin/sh", "-c", "cat message.txt"]
 
-    pid, stdin_fd, stdout_fd, stderr_fd = local_env.execute_command(connection, command)
+    _, stdin_transport, stdout_transport, stderr_transport = local_env.execute_command(connection, command)
 
     try:
-        os.close(stdin_fd)
-        if hasattr(os, "waitpid"):
-            os.waitpid(pid, 0)
-        stdout = _read_all(stdout_fd)
-        stderr = _read_all(stderr_fd)
+        stdin_transport.close()
+        stdout = _drain_transport(stdout_transport)
+        stderr = _drain_transport(stderr_transport)
     finally:
-        _close_fds(stdin_fd, stdout_fd, stderr_fd)
+        stdout_transport.close()
+        stderr_transport.close()
 
     assert stdout == b"hello"
     assert stderr == b""
@@ -85,17 +80,37 @@ def test_execute_command_pipes_stdio(local_env: LocalVirtualEnvironment):
     connection = local_env.establish_connection()
     command = ["/bin/sh", "-c", "tr a-z A-Z < /dev/stdin; printf ERR >&2"]
 
-    pid, stdin_fd, stdout_fd, stderr_fd = local_env.execute_command(connection, command)
+    _, stdin_transport, stdout_transport, stderr_transport = local_env.execute_command(connection, command)
 
     try:
-        os.write(stdin_fd, b"abc")
-        os.close(stdin_fd)
-        if hasattr(os, "waitpid"):
-            os.waitpid(pid, 0)
-        stdout = _read_all(stdout_fd)
-        stderr = _read_all(stderr_fd)
+        stdin_transport.write(b"abc")
+        stdin_transport.close()
+        stdout = _drain_transport(stdout_transport)
+        stderr = _drain_transport(stderr_transport)
     finally:
-        _close_fds(stdin_fd, stdout_fd, stderr_fd)
+        stdout_transport.close()
+        stderr_transport.close()
 
     assert stdout == b"ABC"
     assert stderr == b"ERR"
+
+
+def test_run_command_returns_output(local_env: LocalVirtualEnvironment):
+    local_env.upload_file("message.txt", BytesIO(b"hello"))
+    connection = local_env.establish_connection()
+
+    result = local_env.run_command(connection, ["/bin/sh", "-c", "cat message.txt"]).result(timeout=10)
+
+    assert result.stdout == b"hello"
+    assert result.stderr == b""
+    assert result.exit_code == 0
+
+
+def test_run_command_captures_stderr(local_env: LocalVirtualEnvironment):
+    connection = local_env.establish_connection()
+
+    result = local_env.run_command(connection, ["/bin/sh", "-c", "echo OUT; echo ERR >&2"]).result(timeout=10)
+
+    assert b"OUT" in result.stdout
+    assert b"ERR" in result.stderr
+    assert result.exit_code == 0