fix: skip apiKey injection when explicit AWS credentials are present

Prevents Bedrock requests with accessKeyId/secretAccessKey from
getting a spurious apiKey added via the x-model-api-key header fallback.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: shrey150

packages/server-v3/src/lib/InMemorySessionStore.ts

@@ -216,7 +216,10 @@ export class InMemorySessionStore implements SessionStore {
       ...requestModelClientOptions,
     };
 
-    if (ctx.modelApiKey && modelClientOptions.apiKey === undefined) {
+    const hasExplicitAwsCreds =
+      modelClientOptions.accessKeyId && modelClientOptions.secretAccessKey;
+
+    if (ctx.modelApiKey && !modelClientOptions.apiKey && !hasExplicitAwsCreds) {
       modelClientOptions.apiKey = ctx.modelApiKey;
     }