fix: isolate test env from host CLAUDE_*/CODEX_* variables

- test_runtime_gate: clear env in preflight payload discovery test
- check-prompt-runtime-gate-smoke: filter CLAUDE_*/CODEX_* vars in subprocess env

Fixes 2 pre-existing failures caused by ambient env variable leakage
into _detect_current_host_id_from_env().

Author: Li-Sanze

scripts/check-prompt-runtime-gate-smoke.py

@@ -315,7 +315,7 @@ def _run_gate_scenario(
 
 def _run_gate_cli(*, workspace: Path, home_root: Path, request: str) -> tuple[dict[str, Any], int]:
     script_path = REPO_ROOT / "scripts" / "runtime_gate.py"
-    env = dict(os.environ)
+    env = {k: v for k, v in os.environ.items() if not k.startswith(("CLAUDE_", "CODEX_"))}
     env["HOME"] = str(home_root)
     completed = subprocess.run(
         [

tests/test_runtime_gate.py

@@ -1056,7 +1056,8 @@ def test_gate_preflight_uses_user_home_for_payload_discovery(self) -> None:
             embedded_home = temp_root / "embedded-home"
             _install_payload_manifest_for_gate(home_root=embedded_home)
 
-            with patch("runtime.workspace_preflight.Path.home", return_value=real_home):
+            with patch.dict(os.environ, {}, clear=True), \
+                 patch("runtime.workspace_preflight.Path.home", return_value=real_home):
                 result = enter_runtime_gate(
                     "~go plan demo",
                     workspace_root=workspace,