Improved prompt caching when using Anthropic models on OpenRouter with native tool calling

[chrarnoldus]

Anthropic prompt caching has worked less well since 12 Dec: https://us.posthog.com/project/141915/insights/AhRqQwgk

[changeset-bot]

🦋 Changeset detected

Latest commit: 435c879

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
kilo-code	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Overview

This PR introduces a new Anthropic cache breakpoint implementation (kilocode.ts) that extends caching support to include tool result messages (role: "tool"), which the original implementation didn't handle. This is important for native tool calling scenarios where tool results should also benefit from prompt caching.

Key improvements:

• Properly handles tool role messages alongside user messages for cache breakpoints
• Adds cache control to the last item in array content (including images)
• Finds system prompt from messages array rather than relying on the passed parameter
• Comprehensive test coverage for all scenarios

Files Reviewed (4 files)

• .changeset/cute-flies-dance.md - Changeset for the patch
• src/api/providers/openrouter.ts - Import change to use new implementation
• src/api/transform/caching/kilocode.ts - New caching implementation with tool support
• src/api/transform/caching/__tests__/kilocode.spec.ts - Comprehensive tests