diff --git a/webqa_agent/executor/flash/core/mcp_client.py b/webqa_agent/executor/flash/core/mcp_client.py
index dbe6fe8..3f8110a 100644
--- a/webqa_agent/executor/flash/core/mcp_client.py
+++ b/webqa_agent/executor/flash/core/mcp_client.py
@@ -152,11 +152,13 @@ def start(self, startup_timeout_s: float = _DEFAULT_STARTUP_TIMEOUT) -> None:
 
         Raises MCPError if anything fails within startup_timeout_s.
         """
-        cmd = [self._command] + self._args
-        # Resolve command via PATH explicitly for a clearer error message than
-        # Popen's generic FileNotFoundError.
-        if shutil.which(self._command) is None and not os.path.isabs(self._command):
-            raise MCPError(f'{self.name}: command not found on PATH: {self._command!r}')
+        resolved_command = shutil.which(self._command)
+        if not resolved_command:
+            if not os.path.isabs(self._command):
+                raise MCPError(f'{self.name}: command not found on PATH: {self._command!r}')
+            resolved_command = self._command
+
+        cmd = [resolved_command] + self._args
 
         merged_env = None
         if self._env:
diff --git a/webqa_agent/executor/flash/runner.py b/webqa_agent/executor/flash/runner.py
index cd818dd..b45d5f7 100644
--- a/webqa_agent/executor/flash/runner.py
+++ b/webqa_agent/executor/flash/runner.py
@@ -574,21 +574,27 @@ def _emergency_cleanup() -> None:
 
     atexit.register(_emergency_cleanup)
 
-    _prev_sigterm: Any = None
-    _prev_sighup: Any = None
-    _signals_installed = False
-    try:
-        _prev_sigterm = signal.getsignal(signal.SIGTERM)
-        _prev_sighup = signal.getsignal(signal.SIGHUP)
+    _previous_signal_handlers: dict[int, Any] = {}
+    signals_to_install = [signal.SIGTERM]
+
+    sighup = getattr(signal, "SIGHUP", None)
+    if sighup is not None:
+        signals_to_install.append(sighup)
 
+    try:
         def _signal_handler(signum: int, frame: Any) -> None:
             sys.exit(128 + signum)
 
-        signal.signal(signal.SIGTERM, _signal_handler)
-        signal.signal(signal.SIGHUP, _signal_handler)
-        _signals_installed = True
+        for signum in signals_to_install:
+            _previous_signal_handlers[signum] = signal.getsignal(signum)
+            signal.signal(signum, _signal_handler)
     except ValueError:
-        pass
+        for signum, previous_handler in _previous_signal_handlers.items():
+            try:
+                signal.signal(signum, previous_handler)
+            except ValueError:
+                pass
+        _previous_signal_handlers.clear()
 
     engine: Engine | None = None
     state = _EventLoopState()
@@ -918,9 +924,11 @@ def _on_context_overflow(messages: list[dict]) -> list[dict] | None:
         except Exception:
             pass
         atexit.unregister(_emergency_cleanup)
-        if _signals_installed:
-            signal.signal(signal.SIGTERM, _prev_sigterm)
-            signal.signal(signal.SIGHUP, _prev_sighup)
+        for signum, previous_handler in _previous_signal_handlers.items():
+            try:
+                signal.signal(signum, previous_handler)
+            except ValueError:
+                pass
 
 
 def _resolve_cdp_port(
diff --git a/webqa_agent/executor/flash/tests/test_mcp_client_start.py b/webqa_agent/executor/flash/tests/test_mcp_client_start.py
new file mode 100644
index 0000000..1ee9b10
--- /dev/null
+++ b/webqa_agent/executor/flash/tests/test_mcp_client_start.py
@@ -0,0 +1,88 @@
+"""Tests for MCPServer.start process command resolution."""
+from __future__ import annotations
+
+import io
+from pathlib import Path
+
+import pytest
+
+from webqa_agent.executor.flash.core import mcp_client
+from webqa_agent.executor.flash.core.mcp_client import MCPError, MCPServer
+
+
+class _FakeProc:
+    def __init__(self) -> None:
+        self.stdin = io.BytesIO()
+        self.stdout = io.BytesIO()
+        self.stderr = io.BytesIO()
+        self.pid = 12345
+
+    def wait(self, timeout=None):
+        return 0
+
+    def terminate(self) -> None:
+        pass
+
+    def kill(self) -> None:
+        pass
+
+
+@pytest.fixture
+def isolated_start(monkeypatch):
+    popen_calls = []
+
+    def fake_popen(cmd, **kwargs):
+        popen_calls.append((list(cmd), dict(kwargs)))
+        return _FakeProc()
+
+    monkeypatch.setattr(mcp_client.subprocess, 'Popen', fake_popen)
+    monkeypatch.setattr(MCPServer, '_read_stdout', lambda self: None)
+    monkeypatch.setattr(MCPServer, '_drain_stderr', lambda self: None)
+    monkeypatch.setattr(MCPServer, '_initialize', lambda self, timeout_s: None)
+    monkeypatch.setattr(MCPServer, '_list_tools', lambda self, timeout_s: [])
+    return popen_calls
+
+
+def test_start_uses_resolved_command_from_path(isolated_start, monkeypatch):
+    resolved = r'C:\Users\me\AppData\Roaming\npm\chrome-devtools-mcp.CMD'
+    monkeypatch.setattr(mcp_client.shutil, 'which', lambda command: resolved)
+
+    server = MCPServer(
+        name='browser',
+        command='chrome-devtools-mcp',
+        args=['--headless'],
+    )
+    server.start()
+    server.shutdown()
+
+    assert isolated_start[0][0][0] == resolved
+    assert isolated_start[0][0][1:] == ['--headless']
+
+
+def test_start_raises_when_non_absolute_command_is_not_found(
+    isolated_start, monkeypatch,
+):
+    monkeypatch.setattr(mcp_client.shutil, 'which', lambda command: None)
+
+    server = MCPServer(name='browser', command='missing-mcp-server')
+    with pytest.raises(MCPError, match="command not found on PATH"):
+        server.start()
+
+    assert isolated_start == []
+
+
+def test_start_keeps_absolute_command_when_path_lookup_fails(
+    isolated_start, monkeypatch, tmp_path: Path,
+):
+    absolute_command = str(tmp_path / 'custom-mcp-server')
+    monkeypatch.setattr(mcp_client.shutil, 'which', lambda command: None)
+
+    server = MCPServer(
+        name='custom',
+        command=absolute_command,
+        args=['--stdio'],
+    )
+    server.start()
+    server.shutdown()
+
+    assert isolated_start[0][0] == [absolute_command, '--stdio']
diff --git a/webqa_agent/executor/flash/tests/test_runner_extension_points.py b/webqa_agent/executor/flash/tests/test_runner_extension_points.py
index 36cf920..4aff58b 100644
--- a/webqa_agent/executor/flash/tests/test_runner_extension_points.py
+++ b/webqa_agent/executor/flash/tests/test_runner_extension_points.py
@@ -164,6 +164,66 @@ def test_default_mcp_args_include_security_flags():
         '--chrome-arg=... form instead')
 
 
+def _record_signal_calls(monkeypatch):
+    calls = []
+    previous_handlers = {}
+
+    def fake_getsignal(signum):
+        previous = object()
+        previous_handlers[signum] = previous
+        return previous
+
+    def fake_signal(signum, handler):
+        calls.append((signum, handler))
+
+    monkeypatch.setattr(runner.signal, 'getsignal', fake_getsignal)
+    monkeypatch.setattr(runner.signal, 'signal', fake_signal)
+    return calls, previous_handlers
+
+
+def test_signal_handling_without_sighup_installs_only_sigterm(
+    patched_runner, monkeypatch,
+):
+    """Windows-like platforms do not expose signal.SIGHUP."""
+    monkeypatch.delattr(runner.signal, 'SIGHUP', raising=False)
+    calls, previous_handlers = _record_signal_calls(monkeypatch)
+
+    runner.run_cc_mini(
+        'https://example.com', 'task',
+        api_key='fake-key',
+    )
+
+    sigterm = runner.signal.SIGTERM
+    assert [signum for signum, _handler in calls] == [sigterm, sigterm]
+    assert callable(calls[0][1])
+    assert calls[1] == (sigterm, previous_handlers[sigterm])
+
+
+def test_signal_handling_with_sighup_installs_and_restores_both(
+    patched_runner, monkeypatch,
+):
+    fake_sighup = 99999
+    monkeypatch.setattr(runner.signal, 'SIGHUP', fake_sighup, raising=False)
+    calls, previous_handlers = _record_signal_calls(monkeypatch)
+
+    runner.run_cc_mini(
+        'https://example.com', 'task',
+        api_key='fake-key',
+    )
+
+    sigterm = runner.signal.SIGTERM
+    assert [signum for signum, _handler in calls] == [
+        sigterm,
+        fake_sighup,
+        sigterm,
+        fake_sighup,
+    ]
+    assert callable(calls[0][1])
+    assert callable(calls[1][1])
+    assert calls[2] == (sigterm, previous_handlers[sigterm])
+    assert calls[3] == (fake_sighup, previous_handlers[fake_sighup])
+
+
 def test_force_start_uses_list_pages_not_tab_opening_tools(patched_runner):
     """Force-start must be side-effect-free.