When I create a OpenRouter client, I specify my desired headers as:

			createOpenRouter({
				apiKey: apiKey,
				headers: config.headers
			} as OpenRouterProviderSettings)

Assuming config.headers is {"User-Agent", "my-header-here}, the headers that the implementation actually sends becomes: my-header-here, ai-sdk/openrouter/1.4.0.

Modifying user specified headers without warning or notice is not expected behavior.

This happened with #193