feat: integrate chat credits handling into chat stream processing

lib/chat/__tests__/handleChatStream.test.ts

@@ -54,6 +54,14 @@ vi.mock("@/lib/chat/handleChatCompletion", () => ({
   handleChatCompletion: vi.fn(),
 }));
 
+vi.mock("@/lib/credits/handleChatCredits", () => ({
+  handleChatCredits: vi.fn(),
+}));
+
+vi.mock("@/lib/const", () => ({
+  DEFAULT_MODEL: "openai/gpt-5-mini",
+}));
+
 vi.mock("ai", () => ({
   createUIMessageStream: vi.fn(),
   createUIMessageStreamResponse: vi.fn(),

lib/chat/__tests__/integration/chatEndToEnd.test.ts

@@ -556,8 +556,9 @@ describe("Chat Integration Tests", () => {
       expect(mockDeductCredits).not.toHaveBeenCalled();
     });
 
-    it("handles zero cost gracefully", async () => {
+    it("deducts minimum 1 credit when cost is zero", async () => {
       mockGetCreditUsage.mockResolvedValue(0);
+      mockDeductCredits.mockResolvedValue({ success: true, newBalance: 332 });
 
       await handleChatCredits({
         usage: { promptTokens: 10, completionTokens: 5 },
@@ -566,7 +567,10 @@ describe("Chat Integration Tests", () => {
       });
 
       expect(mockGetCreditUsage).toHaveBeenCalled();
-      expect(mockDeductCredits).not.toHaveBeenCalled();
+      expect(mockDeductCredits).toHaveBeenCalledWith({
+        accountId: "account-123",
+        creditsToDeduct: 1,
+      });
     });
 
     it("catches credit deduction errors without breaking chat flow", async () => {

lib/chat/handleChatStream.ts

@@ -1,10 +1,12 @@
 import { NextRequest, NextResponse } from "next/server";
 import { createUIMessageStream, createUIMessageStreamResponse } from "ai";
 import { handleChatCompletion } from "./handleChatCompletion";
+import { handleChatCredits } from "@/lib/credits/handleChatCredits";
 import { validateChatRequest } from "./validateChatRequest";
 import { setupChatRequest } from "./setupChatRequest";
 import { getCorsHeaders } from "@/lib/networking/getCorsHeaders";
 import generateUUID from "@/lib/uuid/generateUUID";
+import { DEFAULT_MODEL } from "@/lib/const";
 
 /**
  * Handles a streaming chat request.
@@ -28,15 +30,15 @@ export async function handleChatStream(request: NextRequest): Promise<Response>
     const chatConfig = await setupChatRequest(body);
     const { agent } = chatConfig;
 
+    let streamResult: Awaited<ReturnType<typeof agent.stream>> | undefined;
+
     const stream = createUIMessageStream({
       originalMessages: body.messages,
       generateId: generateUUID,
       execute: async options => {
         const { writer } = options;
-        const result = await agent.stream(chatConfig);
-        writer.merge(result.toUIMessageStream());
-        // Note: Credit handling and chat completion handling will be added
-        // as part of the handleChatCredits and handleChatCompletion migrations
+        streamResult = await agent.stream(chatConfig);
+        writer.merge(streamResult.toUIMessageStream());
       },
       onFinish: async event => {
         if (event.isAborted) {
@@ -46,6 +48,13 @@ export async function handleChatStream(request: NextRequest): Promise<Response>
         const responseMessages =
           assistantMessages.length > 0 ? assistantMessages : [event.responseMessage];
         await handleChatCompletion(body, responseMessages);
+        if (streamResult) {
+          await handleChatCredits({
+            usage: await streamResult.usage,
+            model: body.model ?? DEFAULT_MODEL,
+            accountId: body.accountId,
+          });
+        }
       },
       onError: e => {
         console.error("/api/chat onError:", e);

lib/credits/__tests__/handleChatCredits.test.ts

@@ -91,8 +91,9 @@ describe("handleChatCredits", () => {
       expect(mockDeductCredits).not.toHaveBeenCalled();
     });
 
-    it("skips credit deduction when usage cost is 0", async () => {
+    it("deducts minimum 1 credit when usage cost is 0", async () => {
       mockGetCreditUsage.mockResolvedValue(0);
+      mockDeductCredits.mockResolvedValue({ success: true, newBalance: 332 });
 
       await handleChatCredits({
         usage: { promptTokens: 0, completionTokens: 0 },
@@ -101,7 +102,10 @@ describe("handleChatCredits", () => {
       });
 
       expect(mockGetCreditUsage).toHaveBeenCalled();
-      expect(mockDeductCredits).not.toHaveBeenCalled();
+      expect(mockDeductCredits).toHaveBeenCalledWith({
+        accountId: "account-123",
+        creditsToDeduct: 1,
+      });
     });
   });
 

lib/credits/handleChatCredits.ts

@@ -10,7 +10,7 @@ interface HandleChatCreditsParams {
 
 /**
  * Handles credit deduction after chat completion.
- * Calculates usage cost and deducts appropriate credits from the user's account.
+ * Always deducts at least 1 credit when accountId is present (round up from usage cost).
  * @param usage - The language model usage data
  * @param model - The model ID used for the chat
  * @param accountId - The account ID to deduct credits from (optional)
@@ -27,15 +27,12 @@ export const handleChatCredits = async ({
 
   try {
     const usageCost = await getCreditUsage(usage, model);
+    const creditsToDeduct = Math.max(1, Math.round(usageCost * 100));
 
-    if (usageCost > 0) {
-      const creditsToDeduct = Math.max(1, Math.round(usageCost * 100));
-
-      await deductCredits({
-        accountId,
-        creditsToDeduct,
-      });
-    }
+    await deductCredits({
+      accountId,
+      creditsToDeduct,
+    });
   } catch (error) {
     console.error("Failed to handle chat credits:", error);
     // Don't throw error to avoid breaking the chat flow