fix(gateway): preserve max turns after env reload

tests/gateway/test_runtime_env_reload_config_authority.py

@@ -0,0 +1,53 @@
+"""Regression tests for gateway per-turn env reload preserving config authority.
+
+Issue #19158: startup bridges config.yaml agent.max_turns into
+HERMES_MAX_ITERATIONS, but a later per-turn load_dotenv(..., override=True)
+can restore a stale .env HERMES_MAX_ITERATIONS value before the next turn.
+"""
+
+from __future__ import annotations
+
+import os
+from pathlib import Path
+
+import yaml
+
+from gateway import run as gateway_run
+
+
+def test_reload_runtime_env_preserves_config_max_turns(tmp_path: Path, monkeypatch) -> None:
+    hermes_home = tmp_path / ".hermes"
+    hermes_home.mkdir()
+    (hermes_home / "config.yaml").write_text(
+        yaml.safe_dump({"agent": {"max_turns": 9000}}),
+        encoding="utf-8",
+    )
+    (hermes_home / ".env").write_text(
+        "HERMES_MAX_ITERATIONS=90\nOPENROUTER_API_KEY=fresh-key\n",
+        encoding="utf-8",
+    )
+
+    monkeypatch.setattr(gateway_run, "_hermes_home", hermes_home)
+    monkeypatch.setenv("HERMES_MAX_ITERATIONS", "9000")
+    monkeypatch.delenv("OPENROUTER_API_KEY", raising=False)
+
+    gateway_run._reload_runtime_env_preserving_config_authority()
+
+    assert os.environ["OPENROUTER_API_KEY"] == "fresh-key"
+    assert os.environ["HERMES_MAX_ITERATIONS"] == "9000"
+
+
+def test_reload_runtime_env_keeps_env_max_iterations_when_config_omits_key(
+    tmp_path: Path, monkeypatch
+) -> None:
+    hermes_home = tmp_path / ".hermes"
+    hermes_home.mkdir()
+    (hermes_home / "config.yaml").write_text(yaml.safe_dump({"agent": {}}), encoding="utf-8")
+    (hermes_home / ".env").write_text("HERMES_MAX_ITERATIONS=123\n", encoding="utf-8")
+
+    monkeypatch.setattr(gateway_run, "_hermes_home", hermes_home)
+    monkeypatch.delenv("HERMES_MAX_ITERATIONS", raising=False)
+
+    gateway_run._reload_runtime_env_preserving_config_authority()
+
+    assert os.environ["HERMES_MAX_ITERATIONS"] == "123"