Quick Summary

anthropic_messages provider sends system as a flat string, ignoring SystemParts content blocks, which defeats Anthropic prompt caching.

Environment & Tools

• PicoClaw Version: latest main
• Go Version: go 1.25
• AI Model & Provider: Anthropic Claude via anthropic_messages provider
• Operating System: macOS
• Channels: WeCom

📸 Steps to Reproduce

1. Configure anthropic_messages as provider
2. Send a message to the agent
3. Observe the HTTP request — system field is a flat string instead of content blocks array

❌ Actual Behavior

anthropic_messages provider reads msg.Content (concatenated fallback string) instead of msg.SystemParts, resulting in:

• system is a string instead of content blocks array
• No cache_control markers on static blocks
• Dynamic context (## Current Time) mixed in the same string causes the entire system prompt prefix to change every minute, defeating Anthropic prompt caching

provider.go L176-L281:

var systemPrompt string
// ...
case "system":
    systemPrompt = msg.Content  // ← ignores msg.SystemParts
// ...
result["system"] = systemPrompt  // ← flat string, no cache_control

✅ Expected Behavior

Same behavior as the SDK-based anthropic provider — output system as a content blocks array with cache_control: ephemeral on static blocks.

💬 Additional Context

The anthropic (SDK) provider correctly uses SystemParts with per-block cache_control: ephemeral. Fix submitted in PR #2192.