Anthropic forces OpenCode to drop Claude

This is less a courtroom drama than a moat-defense move, and it signals that AI coding tools built on top of model vendors need escape hatches, not just feature parity.

• –Anthropic is drawing a hard line around subscription OAuth, which pushes OpenCode-style clients toward API keys or alternative providers.
• –The removal is broad, not cosmetic: prompt assets, provider enums, auth plugins, and docs all changed, so users will feel the breakage.
• –Review notes point to a possible regression in `packages/opencode/src/session/llm.ts` that strips a non-Anthropic `User-Agent` header too.
• –For developers, the practical lesson is obvious: multi-provider abstraction is now a resilience requirement, not a nice-to-have.