feat: add multi-key auth profile rotation for model providers

src/models/rotating.ts

@@ -0,0 +1,64 @@
+import type { ChatRequest, ChatResponse, ChatStreamEvent, ModelClient } from './types.js';
+
+/**
+ * Model client wrapper that rotates across equivalent auth profiles (e.g. API keys).
+ * Sticky-by-success behavior: keep using the last successful profile until it fails.
+ */
+export class RotatingModelClient implements ModelClient {
+  private readonly clients: ModelClient[];
+  private currentIndex = 0;
+
+  constructor(clients: ModelClient[]) {
+    if (clients.length === 0) {
+      throw new Error('RotatingModelClient requires at least one client');
+    }
+    this.clients = clients;
+  }
+
+  async chat(request: ChatRequest): Promise<ChatResponse> {
+    const start = this.currentIndex;
+    const errors: Error[] = [];
+
+    for (let offset = 0; offset < this.clients.length; offset += 1) {
+      const index = (start + offset) % this.clients.length;
+      const client = this.clients[index];
+      try {
+        const response = await client.chat(request);
+        this.currentIndex = index;
+        return response;
+      } catch (error) {
+        errors.push(error instanceof Error ? error : new Error(String(error)));
+      }
+    }
+
+    throw new Error(`All auth profiles failed: ${errors.map((e) => e.message).join(', ')}`);
+  }
+
+  async *chatStream(request: ChatRequest): AsyncIterable<ChatStreamEvent> {
+    const start = this.currentIndex;
+
+    for (let offset = 0; offset < this.clients.length; offset += 1) {
+      const index = (start + offset) % this.clients.length;
+      const client = this.clients[index];
+      if (!client.chatStream) {
+        continue;
+      }
+
+      let failed = false;
+      for await (const event of client.chatStream(request)) {
+        if (event.type === 'error') {
+          failed = true;
+          break;
+        }
+        yield event;
+      }
+
+      if (!failed) {
+        this.currentIndex = index;
+        return;
+      }
+    }
+
+    yield { type: 'error', error: new Error('All auth profiles failed for streaming') };
+  }
+}