DUX-12033: Remove deprecated Bedrock InvokeModel protocol

[staging-supernova-dx-appf-io]

What this does

Removes the unused Bedrock InvokeModel protocol implementation from ruby_llm. This protocol enabled access to Anthropic's beta features (context_management/server-side prompt caching) via the raw InvokeModel endpoint, but is no longer used in production across agents_app and agent_bridge. The feature was recently deprecated in favor of the standard Converse API which provides equivalent functionality.

Specifically removes:

• BedrockInvokeModel protocol class and submodules (Chat and Streaming implementations)
• All related test coverage for the InvokeModel endpoint
• Configuration option for auto-injecting prompt-cache breakpoints
• Protocol registration from the Bedrock provider

Maintains the appfolio/ruby_llm GitHub dependency and all other fork customizations—only the obsolete InvokeModel-specific code is removed.

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation
• Performance improvement

Scope check

• I read the Contributing Guide
• This aligns with RubyLLM's focus on LLM communication
• This isn't application-specific logic that belongs in user code
• This benefits most users, not just my specific use case

Required for new features

N/A

Quality check

• I ran overcommit --install and all hooks pass
• I tested my changes thoroughly
  • For provider changes: Re-recorded VCR cassettes with bundle exec rake vcr:record[provider_name]
  • All tests pass: bundle exec rspec
• I updated documentation if needed
• I didn't modify auto-generated files manually (models.json, aliases.json)

AI-generated code

• I used AI tools to help write this code
• I have reviewed and understand all generated code (required if above is checked)

API changes

• Breaking change
• New public methods/classes
• Changed method signatures
• No API changes

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Agent session: https://staging.supernova.dx.appf.io/coders/628bd5a6-7f78-4b60-8b04-cd5a0fb0aa5b

[kermitapp]

Jira Issue: https://appfolio.atlassian.net/browse/DUX-12033

[staging-supernova-dx-appf-io]

🤖 Supernova Code Review — View trace

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[staging-supernova-dx-appf-io]

Reviewed this PR — it's a clean, self-contained removal of the unused Bedrock InvokeModel protocol. Verified no dangling references remain to BedrockInvokeModel, bedrock_use_invoke_model, invoke_model?, anthropic_beta, or anthropic_context_management anywhere else in the repo at this branch's head, and the comment updates in mantle_responses.rb and bedrock.rb correctly reflect the simplified routing (mantle vs. Converse only). No actionable bugs, security issues, or missing error handling found — no inline comments.

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