fix(gateway): read API_SERVER_* through profile secret scope in multiplex mode

tests/gateway/test_multiplex_credential_isolation.py

@@ -156,3 +156,41 @@ def worker():
             t.join()
 
         assert seen["home"] == str(prof_b)
+
+
+class TestApiServerEnvIsScoped:
+    """_apply_env_overrides must read API_SERVER_* through the profile scope,
+    not the global os.environ, so a secondary profile is not falsely enabled
+    by the default profile's key loaded into os.environ (#52307)."""
+
+    def test_secondary_profile_scope_without_key_does_not_enable(self, monkeypatch):
+        from gateway.config import _apply_env_overrides, GatewayConfig, Platform
+
+        # Default profile's key is in the global process env (loaded at import).
+        monkeypatch.setenv("API_SERVER_KEY", "global-default-key")
+        ss.set_multiplex_active(True)
+
+        # Secondary profile scope has NO api_server credential.
+        tok = ss.set_secret_scope({"OPENAI_API_KEY": "sk-secondary"})
+        try:
+            config = GatewayConfig()
+            _apply_env_overrides(config)
+            api = config.platforms.get(Platform.API_SERVER)
+            assert api is None or api.enabled is False
+        finally:
+            ss.reset_secret_scope(tok)
+
+    def test_profile_scope_with_key_enables(self, monkeypatch):
+        from gateway.config import _apply_env_overrides, GatewayConfig, Platform
+
+        monkeypatch.delenv("API_SERVER_KEY", raising=False)
+        ss.set_multiplex_active(True)
+        tok = ss.set_secret_scope({"API_SERVER_KEY": "profile-scoped-key"})
+        try:
+            config = GatewayConfig()
+            _apply_env_overrides(config)
+            api = config.platforms.get(Platform.API_SERVER)
+            assert api is not None and api.enabled is True
+            assert api.extra.get("key") == "profile-scoped-key"
+        finally:
+            ss.reset_secret_scope(tok)