Google has an agreement with Anthropic for the usage inside Android Studio.

> Unless previously approved, Anthropic does not allow third party developers to offer claude.ai login [..] for their products.

ref: https://code.claude.com/docs/en/agent-sdk.md

Yes there is a huge gray area. Yes people are getting away with it. That does not mean it's allowed. Anthropic could clarify their terms any day and they don't, on purpose.

Harnesses don't use claude.ai login, they use your `claude` binary.