[loop-cycle-2] feat: hot-reload providers.yaml without restart (#458) (#470)

src/infrastructure/router/api.py

@@ -183,6 +183,22 @@ async def run_health_check(
     }
 
 
+@router.post("/reload")
+async def reload_config(
+    cascade: Annotated[CascadeRouter, Depends(get_cascade_router)],
+) -> dict[str, Any]:
+    """Hot-reload providers.yaml without restart.
+
+    Preserves circuit breaker state and metrics for existing providers.
+    """
+    try:
+        result = cascade.reload_config()
+        return {"status": "ok", **result}
+    except Exception as exc:
+        logger.error("Config reload failed: %s", exc)
+        raise HTTPException(status_code=500, detail=f"Reload failed: {exc}") from exc
+
+
 @router.get("/config")
 async def get_config(
     cascade: Annotated[CascadeRouter, Depends(get_cascade_router)],

src/infrastructure/router/cascade.py

@@ -815,6 +815,64 @@ class CascadeRouter:
         provider.status = ProviderStatus.HEALTHY
         logger.info("Circuit breaker CLOSED for %s", provider.name)
 
+    def reload_config(self) -> dict:
+        """Hot-reload providers.yaml, preserving runtime state.
+
+        Re-reads the config file, rebuilds the provider list, and
+        preserves circuit breaker state and metrics for providers
+        that still exist after reload.
+
+        Returns:
+            Summary dict with added/removed/preserved counts.
+        """
+        # Snapshot current runtime state keyed by provider name
+        old_state: dict[str, tuple[ProviderMetrics, CircuitState, float | None, int, ProviderStatus]] = {}
+        for p in self.providers:
+            old_state[p.name] = (
+                p.metrics,
+                p.circuit_state,
+                p.circuit_opened_at,
+                p.half_open_calls,
+                p.status,
+            )
+
+        old_names = set(old_state.keys())
+
+        # Reload from disk
+        self.providers = []
+        self._load_config()
+
+        # Restore preserved state
+        new_names = {p.name for p in self.providers}
+        preserved = 0
+        for p in self.providers:
+            if p.name in old_state:
+                metrics, circuit, opened_at, half_open, status = old_state[p.name]
+                p.metrics = metrics
+                p.circuit_state = circuit
+                p.circuit_opened_at = opened_at
+                p.half_open_calls = half_open
+                p.status = status
+                preserved += 1
+
+        added = new_names - old_names
+        removed = old_names - new_names
+
+        logger.info(
+            "Config reloaded: %d providers (%d preserved, %d added, %d removed)",
+            len(self.providers),
+            preserved,
+            len(added),
+            len(removed),
+        )
+
+        return {
+            "total_providers": len(self.providers),
+            "preserved": preserved,
+            "added": sorted(added),
+            "removed": sorted(removed),
+        }
+
     def get_metrics(self) -> dict:
         """Get metrics for all providers."""
         return {

tests/infrastructure/test_router_cascade.py

@@ -516,3 +516,183 @@ class TestProviderAvailabilityCheck:
 
         with patch("importlib.util.find_spec", return_value=None):
             assert router._check_provider_available(provider) is False
+
+
+class TestCascadeRouterReload:
+    """Test hot-reload of providers.yaml."""
+
+    def test_reload_preserves_metrics(self, tmp_path):
+        """Test that reload preserves metrics for existing providers."""
+        config = {
+            "providers": [
+                {
+                    "name": "test-openai",
+                    "type": "openai",
+                    "enabled": True,
+                    "priority": 1,
+                    "api_key": "sk-test",
+                }
+            ],
+        }
+        config_path = tmp_path / "providers.yaml"
+        config_path.write_text(yaml.dump(config))
+
+        router = CascadeRouter(config_path=config_path)
+        assert len(router.providers) == 1
+
+        # Simulate some traffic
+        router._record_success(router.providers[0], 150.0)
+        router._record_success(router.providers[0], 250.0)
+        assert router.providers[0].metrics.total_requests == 2
+
+        # Reload
+        result = router.reload_config()
+
+        assert result["total_providers"] == 1
+        assert result["preserved"] == 1
+        assert result["added"] == []
+        assert result["removed"] == []
+        # Metrics survived
+        assert router.providers[0].metrics.total_requests == 2
+        assert router.providers[0].metrics.total_latency_ms == 400.0
+
+    def test_reload_preserves_circuit_breaker(self, tmp_path):
+        """Test that reload preserves circuit breaker state."""
+        config = {
+            "cascade": {"circuit_breaker": {"failure_threshold": 2}},
+            "providers": [
+                {
+                    "name": "test-openai",
+                    "type": "openai",
+                    "enabled": True,
+                    "priority": 1,
+                    "api_key": "sk-test",
+                }
+            ],
+        }
+        config_path = tmp_path / "providers.yaml"
+        config_path.write_text(yaml.dump(config))
+
+        router = CascadeRouter(config_path=config_path)
+
+        # Open circuit breaker
+        for _ in range(2):
+            router._record_failure(router.providers[0])
+        assert router.providers[0].circuit_state == CircuitState.OPEN
+
+        # Reload
+        router.reload_config()
+
+        # Circuit breaker state preserved
+        assert router.providers[0].circuit_state == CircuitState.OPEN
+        assert router.providers[0].status == ProviderStatus.UNHEALTHY
+
+    def test_reload_detects_added_provider(self, tmp_path):
+        """Test that reload detects newly added providers."""
+        config = {
+            "providers": [
+                {
+                    "name": "openai-1",
+                    "type": "openai",
+                    "enabled": True,
+                    "priority": 1,
+                    "api_key": "sk-test",
+                }
+            ],
+        }
+        config_path = tmp_path / "providers.yaml"
+        config_path.write_text(yaml.dump(config))
+
+        router = CascadeRouter(config_path=config_path)
+        assert len(router.providers) == 1
+
+        # Add a second provider to config
+        config["providers"].append(
+            {
+                "name": "anthropic-1",
+                "type": "anthropic",
+                "enabled": True,
+                "priority": 2,
+                "api_key": "sk-ant-test",
+            }
+        )
+        config_path.write_text(yaml.dump(config))
+
+        result = router.reload_config()
+
+        assert result["total_providers"] == 2
+        assert result["preserved"] == 1
+        assert result["added"] == ["anthropic-1"]
+        assert result["removed"] == []
+
+    def test_reload_detects_removed_provider(self, tmp_path):
+        """Test that reload detects removed providers."""
+        config = {
+            "providers": [
+                {
+                    "name": "openai-1",
+                    "type": "openai",
+                    "enabled": True,
+                    "priority": 1,
+                    "api_key": "sk-test",
+                },
+                {
+                    "name": "anthropic-1",
+                    "type": "anthropic",
+                    "enabled": True,
+                    "priority": 2,
+                    "api_key": "sk-ant-test",
+                },
+            ],
+        }
+        config_path = tmp_path / "providers.yaml"
+        config_path.write_text(yaml.dump(config))
+
+        router = CascadeRouter(config_path=config_path)
+        assert len(router.providers) == 2
+
+        # Remove anthropic
+        config["providers"] = [config["providers"][0]]
+        config_path.write_text(yaml.dump(config))
+
+        result = router.reload_config()
+
+        assert result["total_providers"] == 1
+        assert result["preserved"] == 1
+        assert result["removed"] == ["anthropic-1"]
+
+    def test_reload_re_sorts_by_priority(self, tmp_path):
+        """Test that providers are re-sorted by priority after reload."""
+        config = {
+            "providers": [
+                {
+                    "name": "low-priority",
+                    "type": "openai",
+                    "enabled": True,
+                    "priority": 10,
+                    "api_key": "sk-test",
+                },
+                {
+                    "name": "high-priority",
+                    "type": "openai",
+                    "enabled": True,
+                    "priority": 1,
+                    "api_key": "sk-test2",
+                },
+            ],
+        }
+        config_path = tmp_path / "providers.yaml"
+        config_path.write_text(yaml.dump(config))
+
+        router = CascadeRouter(config_path=config_path)
+        assert router.providers[0].name == "high-priority"
+
+        # Swap priorities
+        config["providers"][0]["priority"] = 1
+        config["providers"][1]["priority"] = 10
+        config_path.write_text(yaml.dump(config))
+
+        router.reload_config()
+
+        assert router.providers[0].name == "low-priority"
+        assert router.providers[1].name == "high-priority"