fix: allow custom LLM clients to skip modelApiKey validation in BrowserBase

[gingeekrishna]

This PR fixes issue #899 by updating [api.ts] to allow custom LLM clients (such as AWS Bedrock) to skip the [modelApiKey] validation in the BrowserBase environment. The API key requirement is now enforced only for built-in providers (OpenAI, Anthropic, Google, AISDK), enabling custom LLMs to work without an API key. This resolves the error and supports broader LLM integration.

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[greptile-apps]

Greptile Summary

This PR modifies the API key validation logic in lib/api.ts to resolve issue #899, which prevented custom LLM clients like AWS Bedrock from working in the BrowserBase environment. The change updates the StagehandAPI.init() method to conditionally validate API keys based on the provider type.

The implementation works by parsing the provider name from the modelName parameter (e.g., "openai/gpt-4o" -> "openai") and checking if it matches one of the built-in providers: OpenAI, Anthropic, Google, or AISDK. Only these built-in providers now require a modelApiKey to be provided. Custom LLM clients that don't use these providers can skip the validation entirely, allowing them to handle authentication through their own mechanisms.

This change maintains backward compatibility with existing integrations while expanding support for custom LLM providers. The solution is elegant because it leverages the existing modelName parameter format to infer provider type without requiring additional configuration parameters. For custom clients, the modelApiKey defaults to an empty string when not provided, which aligns with how these clients typically handle authentication internally.

The fix integrates well with the existing Stagehand architecture, which already supports custom LLM clients through the modelClientOptions configuration. This change simply removes the artificial barrier that was preventing these custom clients from working in the BrowserBase environment.

Confidence score: 4/5

• This PR is safe to merge with minimal risk as it relaxes validation for a specific use case without compromising security
• Score reflects well-targeted fix that addresses the core issue without breaking existing functionality for built-in providers
• Pay close attention to the provider name parsing logic and ensure custom clients handle authentication properly

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