fix: add model tier mappings and disable experimental betas

[dgokeeffe]

Summary

• Adds ANTHROPIC_DEFAULT_OPUS_MODEL, ANTHROPIC_DEFAULT_SONNET_MODEL, ANTHROPIC_DEFAULT_HAIKU_MODEL to Claude settings so model tier switching works correctly through the Databricks AI Gateway
• Adds CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS=1 to prevent 400 errors from the gateway rejecting experimental cache_control.scope fields
• Updates default ANTHROPIC_MODEL from databricks-claude-sonnet-4-6 to databricks-claude-opus-4-6

Context

Newer Claude Code versions send cache_control: { type: "ephemeral", scope: "..." } on system messages as an experimental beta feature. The Databricks AI Gateway proxy uses strict validation and rejects the unknown scope field with:

API Error: 400 {"message":"system.2.cache_control.ephemeral.scope: Extra inputs are not permitted"}

Files changed

• app.py — runtime settings written during token rotation
• setup_claude.py — initial settings written at app startup

Test plan

• Deploy to a Databricks workspace and verify Claude Code starts without the 400 error
• Verify model tier switching works (e.g. subagent spawning with haiku/sonnet)

This pull request was AI-assisted by Isaac.

[mpkrass7]

@dgokeeffe can you confirm you deployed to a workspace and you were able to use the anthropic models?

[dgokeeffe]

Find screenshot attached @mpkrass7