fix(zen): 1M context window beta not sent for Opus 4.6 and Sonnet 4.5

[ruslan-kurchenko]

The context-1m-2025-08-07 beta header is only applied to models matching claude-sonnet-*. Opus 4.6 and Sonnet 4.5 silently fall back to the default context limit despite supporting 1M tokens.

Affects both the direct Anthropic API path (anthropic-beta header) and Bedrock path (anthropic_beta body field).

Affected code: packages/console/app/src/routes/zen/util/provider/anthropic.ts

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Claude Opus 4.6 context window limits still 200k #12438: Claude Opus 4.6 context window limits still 200k
• 1M tokens for Opus 4.6 #12338: 1M tokens for Opus 4.6
• [FEATURE]: support anthropic beta 1m token on bedrock #11267: [FEATURE]: support anthropic beta 1m token on bedrock
• anthropic sonnet 4.5 1million token #2886: anthropic sonnet 4.5 1million token

Feel free to ignore if none of these address your specific case.