fix

apps/api/internal/processing/ai.go

@@ -43,10 +43,14 @@ type EnableChecker interface {
 type Completion struct {
 	Text         string
 	PromptTokens int
-	OutputTokens int
-	TotalTokens  int
-	Model        string
-	Raw          any
+	// CachedPromptTokens is the cached subset of PromptTokens (OpenAI
+	// usage.prompt_tokens_details.cached_tokens). Billed far cheaper than fresh
+	// input, so cost accounting must subtract it. 0 when the provider omits it.
+	CachedPromptTokens int
+	OutputTokens       int
+	TotalTokens        int
+	Model              string
+	Raw                any
 }
 
 // Embedder turns text into vectors (OpenAI-compatible /v1/embeddings).