fix: make usage property optional in AnthropicResponse and remove usage assignment in translateChunkToAnthropicEvents message_start

Author: caozhiyuan

src/routes/messages/anthropic-types.ts

@@ -101,7 +101,7 @@ export interface AnthropicResponse {
     | "refusal"
     | null
   stop_sequence: string | null
-  usage: {
+  usage?: {
     input_tokens: number
     output_tokens: number
     cache_creation_input_tokens?: number

src/routes/messages/stream-translation.ts

@@ -41,17 +41,6 @@ export function translateChunkToAnthropicEvents(
         model: chunk.model,
         stop_reason: null,
         stop_sequence: null,
-        usage: {
-          input_tokens:
-            (chunk.usage?.prompt_tokens ?? 0)
-            - (chunk.usage?.prompt_tokens_details?.cached_tokens ?? 0),
-          output_tokens: 0, // Will be updated in message_delta when finished
-          ...(chunk.usage?.prompt_tokens_details?.cached_tokens
-            !== undefined && {
-            cache_read_input_tokens:
-              chunk.usage.prompt_tokens_details.cached_tokens,
-          }),
-        },
       },
     })
     state.messageStartSent = true

tests/anthropic-response.test.ts

@@ -100,7 +100,10 @@ describe("OpenAI to Anthropic Non-Streaming Response Translation", () => {
 
     expect(anthropicResponse.id).toBe("chatcmpl-123")
     expect(anthropicResponse.stop_reason).toBe("end_turn")
-    expect(anthropicResponse.usage.input_tokens).toBe(9)
+    expect(anthropicResponse.usage).toBeDefined()
+    if (anthropicResponse.usage) {
+      expect(anthropicResponse.usage.input_tokens).toBe(9)
+    }
     expect(anthropicResponse.content[0].type).toBe("text")
     if (anthropicResponse.content[0].type === "text") {
       expect(anthropicResponse.content[0].text).toBe(