feat(openrouter): add response caching support (#19132)

Enable OpenRouter's response caching feature (beta) via X-OpenRouter-Cache
headers. When enabled, identical API requests return cached responses for
free (zero billing), reducing both latency and cost.

Configuration via config.yaml:
  openrouter:
    response_cache: true       # default: on
    response_cache_ttl: 300    # 1-86400 seconds

Changes:
- Add openrouter config section to DEFAULT_CONFIG (response_cache + TTL)
- Add build_or_headers() in auxiliary_client.py that builds attribution
  headers plus optional cache headers based on config
- Replace inline _OR_HEADERS dicts with build_or_headers() at all 5 sites:
  run_agent.py __init__, _apply_client_headers_for_base_url(), and
  auxiliary_client.py _try_openrouter() + _to_async_client()
- Add _check_openrouter_cache_status() method to AIAgent that reads
  X-OpenRouter-Cache-Status from streaming response headers and logs
  HIT/MISS status
- Document in cli-config.yaml.example
- Add 28 tests (22 unit + 6 integration)

Ref: https://openrouter.ai/docs/guides/features/response-caching

tests/agent/test_openrouter_response_cache.py

@@ -0,0 +1,284 @@
+"""Tests for OpenRouter response caching header injection."""
+
+from types import SimpleNamespace
+from unittest.mock import patch
+
+import pytest
+
+
+# ---------------------------------------------------------------------------
+# build_or_headers
+# ---------------------------------------------------------------------------
+
+class TestBuildOrHeaders:
+    """Test the build_or_headers() helper in agent/auxiliary_client.py."""
+
+    def test_base_attribution_always_present(self):
+        """Attribution headers must always be included regardless of cache setting."""
+        from agent.auxiliary_client import build_or_headers
+
+        headers = build_or_headers(or_config={"response_cache": False})
+        assert headers["HTTP-Referer"] == "https://hermes-agent.nousresearch.com"
+        assert headers["X-OpenRouter-Title"] == "Hermes Agent"
+        assert headers["X-OpenRouter-Categories"] == "productivity,cli-agent"
+
+    def test_cache_enabled(self):
+        """When response_cache is True, X-OpenRouter-Cache header is set."""
+        from agent.auxiliary_client import build_or_headers
+
+        headers = build_or_headers(or_config={"response_cache": True})
+        assert headers["X-OpenRouter-Cache"] == "true"
+
+    def test_cache_disabled(self):
+        """When response_cache is False, no cache header is sent."""
+        from agent.auxiliary_client import build_or_headers
+
+        headers = build_or_headers(or_config={"response_cache": False})
+        assert "X-OpenRouter-Cache" not in headers
+        assert "X-OpenRouter-Cache-TTL" not in headers
+
+    def test_cache_disabled_by_default_empty_config(self):
+        """Empty config dict means no cache headers (response_cache defaults to False)."""
+        from agent.auxiliary_client import build_or_headers
+
+        headers = build_or_headers(or_config={})
+        assert "X-OpenRouter-Cache" not in headers
+
+    def test_ttl_default(self):
+        """Default TTL (300) is included when cache is enabled."""
+        from agent.auxiliary_client import build_or_headers
+
+        headers = build_or_headers(or_config={"response_cache": True, "response_cache_ttl": 300})
+        assert headers["X-OpenRouter-Cache-TTL"] == "300"
+
+    def test_ttl_custom(self):
+        """Custom TTL values within range are sent."""
+        from agent.auxiliary_client import build_or_headers
+
+        headers = build_or_headers(or_config={"response_cache": True, "response_cache_ttl": 3600})
+        assert headers["X-OpenRouter-Cache-TTL"] == "3600"
+
+    def test_ttl_max(self):
+        """Maximum TTL (86400) is accepted."""
+        from agent.auxiliary_client import build_or_headers
+
+        headers = build_or_headers(or_config={"response_cache": True, "response_cache_ttl": 86400})
+        assert headers["X-OpenRouter-Cache-TTL"] == "86400"
+
+    def test_ttl_out_of_range_too_high(self):
+        """TTL above 86400 is silently ignored (no TTL header sent)."""
+        from agent.auxiliary_client import build_or_headers
+
+        headers = build_or_headers(or_config={"response_cache": True, "response_cache_ttl": 100000})
+        assert "X-OpenRouter-Cache-TTL" not in headers
+        # But cache is still enabled
+        assert headers["X-OpenRouter-Cache"] == "true"
+
+    def test_ttl_out_of_range_zero(self):
+        """TTL of 0 is below minimum — no TTL header sent."""
+        from agent.auxiliary_client import build_or_headers
+
+        headers = build_or_headers(or_config={"response_cache": True, "response_cache_ttl": 0})
+        assert "X-OpenRouter-Cache-TTL" not in headers
+
+    def test_ttl_negative(self):
+        """Negative TTL is ignored."""
+        from agent.auxiliary_client import build_or_headers
+
+        headers = build_or_headers(or_config={"response_cache": True, "response_cache_ttl": -5})
+        assert "X-OpenRouter-Cache-TTL" not in headers
+
+    def test_ttl_not_a_number(self):
+        """Non-numeric TTL is ignored."""
+        from agent.auxiliary_client import build_or_headers
+
+        headers = build_or_headers(or_config={"response_cache": True, "response_cache_ttl": "five"})
+        assert "X-OpenRouter-Cache-TTL" not in headers
+
+    def test_ttl_float_truncated(self):
+        """Float TTL values are truncated to int."""
+        from agent.auxiliary_client import build_or_headers
+
+        headers = build_or_headers(or_config={"response_cache": True, "response_cache_ttl": 600.7})
+        assert headers["X-OpenRouter-Cache-TTL"] == "600"
+
+    def test_returns_fresh_dict(self):
+        """Each call returns a new dict so mutations don't leak."""
+        from agent.auxiliary_client import build_or_headers
+
+        cfg = {"response_cache": True}
+        h1 = build_or_headers(or_config=cfg)
+        h2 = build_or_headers(or_config=cfg)
+        assert h1 is not h2
+        assert h1 == h2
+
+    def test_none_config_falls_back_to_load_config(self):
+        """When or_config is None, build_or_headers reads from load_config()."""
+        from agent.auxiliary_client import build_or_headers
+
+        fake_cfg = {
+            "openrouter": {"response_cache": True, "response_cache_ttl": 900},
+        }
+        with patch("hermes_cli.config.load_config", return_value=fake_cfg):
+            headers = build_or_headers(or_config=None)
+        assert headers["X-OpenRouter-Cache"] == "true"
+        assert headers["X-OpenRouter-Cache-TTL"] == "900"
+
+    def test_none_config_load_config_fails_gracefully(self):
+        """When load_config() fails, build_or_headers still returns base headers."""
+        from agent.auxiliary_client import build_or_headers
+
+        with patch("hermes_cli.config.load_config", side_effect=RuntimeError("boom")):
+            headers = build_or_headers(or_config=None)
+        # Should have base attribution but no cache headers
+        assert "HTTP-Referer" in headers
+        assert "X-OpenRouter-Cache" not in headers
+
+
+# ---------------------------------------------------------------------------
+# Environment variable overrides
+# ---------------------------------------------------------------------------
+
+class TestEnvVarOverrides:
+    """Test env var precedence over config.yaml for response caching."""
+
+    def test_env_enables_cache(self, monkeypatch):
+        """HERMES_OPENROUTER_CACHE=true enables cache even when config disables it."""
+        from agent.auxiliary_client import build_or_headers
+
+        monkeypatch.setenv("HERMES_OPENROUTER_CACHE", "true")
+        headers = build_or_headers(or_config={"response_cache": False})
+        assert headers["X-OpenRouter-Cache"] == "true"
+
+    def test_env_disables_cache(self, monkeypatch):
+        """HERMES_OPENROUTER_CACHE=false disables cache even when config enables it."""
+        from agent.auxiliary_client import build_or_headers
+
+        monkeypatch.setenv("HERMES_OPENROUTER_CACHE", "false")
+        headers = build_or_headers(or_config={"response_cache": True})
+        assert "X-OpenRouter-Cache" not in headers
+
+    @pytest.mark.parametrize("value", ["1", "true", "TRUE", "yes", "Yes", "on"])
+    def test_truthy_values(self, monkeypatch, value):
+        """Various truthy strings enable caching."""
+        from agent.auxiliary_client import build_or_headers
+
+        monkeypatch.setenv("HERMES_OPENROUTER_CACHE", value)
+        headers = build_or_headers(or_config={})
+        assert headers["X-OpenRouter-Cache"] == "true"
+
+    @pytest.mark.parametrize("value", ["0", "false", "no", "off", "maybe", ""])
+    def test_non_truthy_values(self, monkeypatch, value):
+        """Non-truthy strings do not enable caching (empty falls through to config)."""
+        from agent.auxiliary_client import build_or_headers
+
+        monkeypatch.setenv("HERMES_OPENROUTER_CACHE", value)
+        # Empty string falls through to config; others are explicitly non-truthy
+        if value == "":
+            # Empty env var falls through to config default (False)
+            headers = build_or_headers(or_config={"response_cache": False})
+        else:
+            headers = build_or_headers(or_config={"response_cache": True})
+        assert "X-OpenRouter-Cache" not in headers
+
+    def test_env_ttl_overrides_config(self, monkeypatch):
+        """HERMES_OPENROUTER_CACHE_TTL overrides config TTL."""
+        from agent.auxiliary_client import build_or_headers
+
+        monkeypatch.setenv("HERMES_OPENROUTER_CACHE", "true")
+        monkeypatch.setenv("HERMES_OPENROUTER_CACHE_TTL", "1800")
+        headers = build_or_headers(or_config={"response_cache_ttl": 300})
+        assert headers["X-OpenRouter-Cache-TTL"] == "1800"
+
+    @pytest.mark.parametrize("ttl", ["0", "86401", "abc", "-1", "12.5"])
+    def test_invalid_env_ttl_dropped(self, monkeypatch, ttl):
+        """Invalid TTL env values are ignored; cache still enabled without TTL."""
+        from agent.auxiliary_client import build_or_headers
+
+        monkeypatch.setenv("HERMES_OPENROUTER_CACHE", "1")
+        monkeypatch.setenv("HERMES_OPENROUTER_CACHE_TTL", ttl)
+        headers = build_or_headers(or_config={})
+        assert headers["X-OpenRouter-Cache"] == "true"
+        assert "X-OpenRouter-Cache-TTL" not in headers
+
+    @pytest.mark.parametrize("ttl", ["1", "300", "86400"])
+    def test_valid_env_ttl_boundaries(self, monkeypatch, ttl):
+        """Boundary TTL values (1, 300, 86400) are accepted."""
+        from agent.auxiliary_client import build_or_headers
+
+        monkeypatch.setenv("HERMES_OPENROUTER_CACHE", "yes")
+        monkeypatch.setenv("HERMES_OPENROUTER_CACHE_TTL", ttl)
+        assert build_or_headers(or_config={})["X-OpenRouter-Cache-TTL"] == ttl
+
+    def test_no_env_vars_falls_through_to_config(self, monkeypatch):
+        """Without env vars, config.yaml controls behavior."""
+        from agent.auxiliary_client import build_or_headers
+
+        monkeypatch.delenv("HERMES_OPENROUTER_CACHE", raising=False)
+        monkeypatch.delenv("HERMES_OPENROUTER_CACHE_TTL", raising=False)
+        headers = build_or_headers(or_config={"response_cache": True, "response_cache_ttl": 600})
+        assert headers["X-OpenRouter-Cache"] == "true"
+        assert headers["X-OpenRouter-Cache-TTL"] == "600"
+
+class TestDefaultConfig:
+    """Verify the openrouter config section is in DEFAULT_CONFIG."""
+
+    def test_openrouter_section_exists(self):
+        from hermes_cli.config import DEFAULT_CONFIG
+
+        assert "openrouter" in DEFAULT_CONFIG
+        or_cfg = DEFAULT_CONFIG["openrouter"]
+        assert or_cfg["response_cache"] is True
+        assert or_cfg["response_cache_ttl"] == 300
+
+
+# ---------------------------------------------------------------------------
+# _check_openrouter_cache_status
+# ---------------------------------------------------------------------------
+
+class TestCheckOpenrouterCacheStatus:
+    """Test the _check_openrouter_cache_status method on AIAgent."""
+
+    def _make_agent(self):
+        """Create a minimal AIAgent-like object with just the method under test."""
+        from run_agent import AIAgent
+
+        # Use object.__new__ to skip __init__, then set the attributes we need
+        agent = object.__new__(AIAgent)
+        agent._or_cache_hits = 0
+        return agent
+
+    def test_hit_increments_counter(self):
+        agent = self._make_agent()
+        resp = SimpleNamespace(headers={"x-openrouter-cache-status": "HIT"})
+        agent._check_openrouter_cache_status(resp)
+        assert agent._or_cache_hits == 1
+        # Second hit increments
+        agent._check_openrouter_cache_status(resp)
+        assert agent._or_cache_hits == 2
+
+    def test_miss_does_not_increment(self):
+        agent = self._make_agent()
+        resp = SimpleNamespace(headers={"x-openrouter-cache-status": "MISS"})
+        agent._check_openrouter_cache_status(resp)
+        assert getattr(agent, "_or_cache_hits", 0) == 0
+
+    def test_no_header_is_noop(self):
+        agent = self._make_agent()
+        resp = SimpleNamespace(headers={})
+        agent._check_openrouter_cache_status(resp)
+        assert getattr(agent, "_or_cache_hits", 0) == 0
+
+    def test_none_response_is_safe(self):
+        agent = self._make_agent()
+        agent._check_openrouter_cache_status(None)  # no crash
+
+    def test_no_headers_attr_is_safe(self):
+        agent = self._make_agent()
+        agent._check_openrouter_cache_status(object())  # no crash
+
+    def test_case_insensitive(self):
+        agent = self._make_agent()
+        resp = SimpleNamespace(headers={"x-openrouter-cache-status": "hit"})
+        agent._check_openrouter_cache_status(resp)
+        assert agent._or_cache_hits == 1