feat(exec): support allowed_env_keys to pass specified env vars to subprocess

Add allowed_env_keys config field to selectively forward host environment variables (e.g. GOPATH, JAVA_HOME) into the sandboxed subprocess environment, while keeping the default allow-list unchanged.

tests/tools/test_exec_env.py

@@ -43,3 +43,34 @@ async def test_exec_path_append_preserves_system_path():
     tool = ExecTool(path_append="/opt/custom/bin")
     result = await tool.execute(command="ls /")
     assert "Exit code: 0" in result
+
+
+@_UNIX_ONLY
+@pytest.mark.asyncio
+async def test_exec_allowed_env_keys_passthrough(monkeypatch):
+    """Env vars listed in allowed_env_keys should be visible to commands."""
+    monkeypatch.setenv("MY_CUSTOM_VAR", "hello-from-config")
+    tool = ExecTool(allowed_env_keys=["MY_CUSTOM_VAR"])
+    result = await tool.execute(command="printenv MY_CUSTOM_VAR")
+    assert "hello-from-config" in result
+
+
+@_UNIX_ONLY
+@pytest.mark.asyncio
+async def test_exec_allowed_env_keys_does_not_leak_others(monkeypatch):
+    """Env vars NOT in allowed_env_keys should still be blocked."""
+    monkeypatch.setenv("MY_CUSTOM_VAR", "hello-from-config")
+    monkeypatch.setenv("MY_SECRET_VAR", "secret-value")
+    tool = ExecTool(allowed_env_keys=["MY_CUSTOM_VAR"])
+    result = await tool.execute(command="printenv MY_SECRET_VAR")
+    assert "secret-value" not in result
+
+
+@_UNIX_ONLY
+@pytest.mark.asyncio
+async def test_exec_allowed_env_keys_missing_var_ignored(monkeypatch):
+    """If an allowed key is not set in the parent process, it should be silently skipped."""
+    monkeypatch.delenv("NONEXISTENT_VAR_12345", raising=False)
+    tool = ExecTool(allowed_env_keys=["NONEXISTENT_VAR_12345"])
+    result = await tool.execute(command="printenv NONEXISTENT_VAR_12345")
+    assert "Exit code: 1" in result