feat: implement 7 major features — rotation strategies, observability, proxy, config, resilience, LangChain, auto-discovery

Add 7 new rotation strategies (cost-first, latency-first, round-robin,
priority-selection, session-stickiness, rate-limit-aware, load-balanced),
Prometheus metrics connector, enhanced proxy server (health/ready/metrics
endpoints, rate limiting, request IDs, graceful shutdown), config
validation with hot-reload and 5 templates, resilience patterns (circuit
breaker, timeout, streaming checkpoint mixins), LangChain/LangGraph
adapter, and provider auto-discovery with model registry.

47 connectors registered. 1,028 tests passing (91 new).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: apartsin

docs/cdk/Mixins.md

@@ -1636,3 +1636,89 @@ class CachedHttpProvider {
     }
 }
 ```
+
+---
+
+## CircuitBreakerMixin
+
+Implements the circuit breaker pattern to prevent cascading failures when a provider becomes unhealthy. When a provider's error count exceeds the failure threshold, the circuit opens and requests fail fast without calling the provider. After a reset timeout, a single probe request is allowed; if it succeeds, the circuit closes.
+
+### States
+
+| State | Description |
+| --- | --- |
+| `CLOSED` | Normal operation. Requests pass through. |
+| `OPEN` | Provider is unhealthy. Requests fail fast with `CircuitOpenError`. |
+| `HALF_OPEN` | Probe mode. A limited number of requests pass through to test recovery. |
+
+### Methods
+
+| Method | Signature | Description |
+| --- | --- | --- |
+| `configure_circuit_breaker` | `(failure_threshold, reset_timeout, half_open_max, success_threshold)` | Set circuit breaker parameters. |
+| `check_circuit` | `()` | Verify the circuit allows a request. Raises `CircuitOpenError` if open. |
+| `record_success` | `()` | Record a successful request. Closes circuit in half-open state. |
+| `record_failure` | `()` | Record a failed request. Opens circuit when threshold is reached. |
+| `reset_circuit` | `()` | Manually reset the circuit to CLOSED. |
+| `circuit_breaker_stats` | `()` | Return current state, failure count, and config. |
+
+### Configuration
+
+| Parameter | Type | Default | Description |
+| --- | --- | --- | --- |
+| `failure_threshold` | `int` | `5` | Consecutive failures to trip the circuit. |
+| `reset_timeout` | `float` | `60.0` | Seconds before OPEN transitions to HALF_OPEN. |
+| `half_open_max` | `int` | `1` | Max probe requests in HALF_OPEN state. |
+| `success_threshold` | `int` | `1` | Successes in HALF_OPEN needed to close. |
+
+---
+
+## TimeoutMixin
+
+Enforces per-request timeouts by wrapping async operations with `asyncio.wait_for`. Raises `RequestTimeoutError` when exceeded.
+
+### Methods
+
+| Method | Signature | Description |
+| --- | --- | --- |
+| `configure_timeout` | `(default, streaming, streaming_total, connect)` | Set timeout values in seconds. |
+| `with_timeout` | `(coro, timeout?, operation?)` | Execute a coroutine with a timeout. |
+| `with_stream_timeout` | `(aiter, first_chunk_timeout?, total_timeout?)` | Wrap a streaming async iterator with timeouts. |
+
+### Configuration
+
+| Parameter | Type | Default | Description |
+| --- | --- | --- | --- |
+| `default` | `float` | `30.0` | Non-streaming request timeout. |
+| `streaming` | `float` | `60.0` | First-chunk timeout for streams. |
+| `streaming_total` | `float` | `300.0` | Total stream duration timeout. |
+| `connect` | `float` | `10.0` | Connection establishment timeout. |
+
+---
+
+## StreamingCheckpointMixin
+
+Tracks streaming response progress so that interrupted streams can be detected and potentially resumed. Buffers content and token counts per active stream.
+
+### Methods
+
+| Method | Signature | Description |
+| --- | --- | --- |
+| `configure_checkpoints` | `(max_buffer_tokens, checkpoint_interval, max_checkpoints)` | Set checkpoint parameters. |
+| `create_checkpoint` | `(request_id, model_id?)` | Create and register a new stream checkpoint. |
+| `get_checkpoint` | `(request_id)` | Retrieve a checkpoint by request ID. |
+| `remove_checkpoint` | `(request_id)` | Remove a completed checkpoint. |
+| `active_checkpoints` | `()` | Return all incomplete checkpoints. |
+| `checkpoint_stats` | `()` | Return summary statistics. |
+
+### StreamCheckpoint
+
+| Field | Type | Description |
+| --- | --- | --- |
+| `request_id` | `str` | Unique request identifier. |
+| `model_id` | `str` | Model generating the stream. |
+| `tokens_received` | `int` | Total tokens received. |
+| `content_buffer` | `str` | Accumulated text. |
+| `is_complete` | `bool` | Whether the stream finished normally. |
+| `duration` | `float` | Elapsed time in seconds (property). |
+| `tokens_per_second` | `float` | Throughput metric (property). |

samples/connectors/typescript/customDiscovery.ts

@@ -237,9 +237,9 @@ class YamlDiscoveryConnector implements DiscoveryConnector {
             errors.push(`Failed to load registry file: ${message}`);
             this.syncStatus.status = "error";
             return {
-                new_models: [],
-                deprecated_models: [],
-                updated_models: [],
+                newModels: [],
+                deprecatedModels: [],
+                updatedModels: [],
                 errors,
             };
         }
@@ -291,16 +291,16 @@ class YamlDiscoveryConnector implements DiscoveryConnector {
         // Update sync status.
         const now = new Date();
         this.syncStatus = {
-            last_sync: now,
-            next_sync: new Date(now.getTime() + this.syncIntervalMs),
-            models_synced: modelsToSync.length,
+            lastSync: now,
+            nextSync: new Date(now.getTime() + this.syncIntervalMs),
+            modelsSynced: modelsToSync.length,
             status: errors.length > 0 ? "completed_with_errors" : "idle",
         };
 
         return {
-            new_models: newModels,
-            deprecated_models: [...new Set(deprecatedModels)], // deduplicate
-            updated_models: updatedModels,
+            newModels: newModels,
+            deprecatedModels: [...new Set(deprecatedModels)], // deduplicate
+            updatedModels: updatedModels,
             errors,
         };
     }
@@ -333,7 +333,7 @@ class YamlDiscoveryConnector implements DiscoveryConnector {
 
         if (!provider) {
             const result: ProbeResult = {
-                provider_id: providerId,
+                providerId: providerId,
                 success: false,
                 error: `Provider "${providerId}" not found in registry`,
             };
@@ -342,8 +342,8 @@ class YamlDiscoveryConnector implements DiscoveryConnector {
         }
 
         const healthUrl = this.buildHealthUrl(provider);
-        const method = (provider.health_method ?? "GET").toUpperCase();
-        const expectedStatus = provider.health_expected_status ?? 200;
+        const method = (provider.healthMethod ?? "GET").toUpperCase();
+        const expectedStatus = provider.healthExpectedStatus ?? 200;
 
         const startTime = performance.now();
 
@@ -369,10 +369,10 @@ class YamlDiscoveryConnector implements DiscoveryConnector {
             const success = response.status === expectedStatus;
 
             const result: ProbeResult = {
-                provider_id: providerId,
+                providerId: providerId,
                 success,
-                latency_ms: Math.round(latencyMs * 100) / 100,
-                status_code: response.status,
+                latencyMs: Math.round(latencyMs * 100) / 100,
+                statusCode: response.status,
                 error: success
                     ? undefined
                     : `Unexpected status ${response.status} (expected ${expectedStatus})`,
@@ -397,9 +397,9 @@ class YamlDiscoveryConnector implements DiscoveryConnector {
             }
 
             const result: ProbeResult = {
-                provider_id: providerId,
+                providerId: providerId,
                 success: false,
-                latency_ms: Math.round(latencyMs * 100) / 100,
+                latencyMs: Math.round(latencyMs * 100) / 100,
                 error: errorDescription,
             };
 
@@ -493,8 +493,8 @@ class YamlDiscoveryConnector implements DiscoveryConnector {
         current: YamlModelEntry,
     ): boolean {
         if (previous.status !== current.status) return true;
-        if (previous.context_window !== current.context_window) return true;
-        if (previous.max_output_tokens !== current.max_output_tokens) return true;
+        if (previous.contextWindow !== current.contextWindow) return true;
+        if (previous.maxOutputTokens !== current.maxOutputTokens) return true;
 
         // Compare capabilities arrays.
         if (previous.capabilities.length !== current.capabilities.length) return true;
@@ -506,8 +506,8 @@ class YamlDiscoveryConnector implements DiscoveryConnector {
         // Compare pricing if present.
         if (previous.pricing && current.pricing) {
             if (
-                previous.pricing.input_per_1k_tokens !== current.pricing.input_per_1k_tokens ||
-                previous.pricing.output_per_1k_tokens !== current.pricing.output_per_1k_tokens
+                previous.pricing.inputPer1kTokens !== current.pricing.inputPer1kTokens ||
+                previous.pricing.outputPer1kTokens !== current.pricing.outputPer1kTokens
             ) {
                 return true;
             }
@@ -530,19 +530,19 @@ class YamlDiscoveryConnector implements DiscoveryConnector {
 
     /** Build the full health endpoint URL for a provider. */
     private buildHealthUrl(provider: YamlProviderEntry): string {
-        const base = provider.base_url.replace(/\/+$/, "");
-        const endpoint = provider.health_endpoint.startsWith("/")
-            ? provider.health_endpoint
-            : `/${provider.health_endpoint}`;
+        const base = provider.baseUrl.replace(/\/+$/, "");
+        const endpoint = provider.healthEndpoint.startsWith("/")
+            ? provider.healthEndpoint
+            : `/${provider.healthEndpoint}`;
         return `${base}${endpoint}`;
     }
 
     /** Record a probe result in the rolling history. */
     private recordProbeResult(result: ProbeResult): void {
-        let history = this.probeHistory.get(result.provider_id);
+        let history = this.probeHistory.get(result.providerId);
         if (!history) {
             history = [];
-            this.probeHistory.set(result.provider_id, history);
+            this.probeHistory.set(result.providerId, history);
         }
 
         // Add to the front (newest first).
@@ -570,9 +570,9 @@ class YamlDiscoveryConnector implements DiscoveryConnector {
 
         if (history.length === 0) {
             return {
-                provider_id: providerId,
+                providerId: providerId,
                 available: true, // assume available until proven otherwise
-                availability_score: 1.0,
+                availabilityScore: 1.0,
                 timestamp: now,
             };
         }
@@ -597,23 +597,23 @@ class YamlDiscoveryConnector implements DiscoveryConnector {
 
         // Compute average latency from successful probes.
         const successfulProbes = history.filter(
-            (r) => r.success && r.latency_ms !== undefined,
+            (r) => r.success && r.latencyMs !== undefined,
         );
         const avgLatency =
             successfulProbes.length > 0
-                ? successfulProbes.reduce((sum, r) => sum + (r.latency_ms ?? 0), 0) /
+                ? successfulProbes.reduce((sum, r) => sum + (r.latencyMs ?? 0), 0) /
                   successfulProbes.length
                 : undefined;
 
         return {
-            provider_id: providerId,
+            providerId: providerId,
             available,
-            latency_ms: avgLatency !== undefined
+            latencyMs: avgLatency !== undefined
                 ? Math.round(avgLatency * 100) / 100
-                : latest.latency_ms,
-            status_code: latest.status_code,
+                : latest.latencyMs,
+            statusCode: latest.statusCode,
             error: latest.error,
-            availability_score: Math.round(availabilityScore * 1000) / 1000,
+            availabilityScore: Math.round(availabilityScore * 1000) / 1000,
             timestamp: now,
         };
     }