chore: fix remaining linting issues in caching code

- Use max() built-in instead of if statement (modernize)
- Remove unused buildAnthropicCacheOptions function
- Remove unused anthropic import

internal/agent/cache_control.go

@@ -45,10 +45,7 @@ func applyCacheControlToMessages(messages []fantasy.Message) []fantasy.Message {
 	}
 
 	// Apply cache control to the last 2 messages
-	startIdx := len(result) - 2
-	if startIdx < 0 {
-		startIdx = 0
-	}
+	startIdx := max(len(result)-2, 0)
 	for i := startIdx; i < len(result); i++ {
 		// Only apply if not already set (avoid double-setting system message)
 		if i != lastSystemIdx {

internal/models/cache_options.go

@@ -7,7 +7,6 @@ import (
 	"os"
 
 	"charm.land/fantasy"
-	"charm.land/fantasy/providers/anthropic"
 	"charm.land/fantasy/providers/openai"
 )
 
@@ -44,16 +43,6 @@ func buildCacheProviderOptions(modelInfo *ModelInfo, config *ProviderConfig) fan
 	}
 }
 
-// buildAnthropicCacheOptions enables ephemeral caching for Anthropic models.
-// Used for message-level caching to avoid provider-level type conflicts.
-func buildAnthropicCacheOptions() fantasy.ProviderOptions {
-	return anthropic.NewProviderCacheControlOptions(&anthropic.ProviderCacheControlOptions{
-		CacheControl: anthropic.CacheControl{
-			Type: "ephemeral",
-		},
-	})
-}
-
 // buildOpenAICacheOptions enables prompt caching for OpenAI models.
 // Uses a deterministic cache key based on system prompt and model ID.
 func buildOpenAICacheOptions(config *ProviderConfig, modelID string) fantasy.ProviderOptions {