Function addAnthropicPromptCaching

coderd/x/chatd/chatloop/chatloop.go:1932–1956

addAnthropicPromptCaching mutates messages in-place, setting ProviderOptions for Anthropic prompt caching on the last system message and the final two messages.

(messages []fantasy.Message)

// ProviderOptions for Anthropic prompt caching on the last system
// message and the final two messages.
func addAnthropicPromptCaching(messages []fantasy.Message) {
	for i := range messages {
		messages[i].ProviderOptions = nil
	}

	providerOption := fantasy.ProviderOptions{
		fantasyanthropic.Name: &fantasyanthropic.ProviderCacheControlOptions{
			CacheControl: fantasyanthropic.CacheControl{Type: "ephemeral"},
		},
	}

	lastSystemRoleIdx := -1
	systemMessageUpdated := false
	for i, msg := range messages {
		if msg.Role == fantasy.MessageRoleSystem {
			lastSystemRoleIdx = i
		} else if !systemMessageUpdated && lastSystemRoleIdx >= 0 {
			messages[lastSystemRoleIdx].ProviderOptions = providerOption
			systemMessageUpdated = true
		}
		if i > len(messages)-3 {
			messages[i].ProviderOptions = providerOption
		}
	}
}

// recordToolResultTimestamp lazily initializes the
// toolResultCreatedAt map on the stepResult and records