feat: credit enforcement on chat, workflow export/import

- Wire up monthly credit checking and incrementing for both chat
  streaming routes. Credits checked before LLM call (429 if exceeded),
  incremented after successful response. Auto-resets when past reset
  date. Limit via MONTHLY_CREDIT_LIMIT env var (PR Open-Legal-Products#157).
- Add GET /workflows/:id/export (.mikeworkflow.json download) and
  POST /workflows/import endpoints for portable workflow transfer
  between environments (PR Open-Legal-Products#59).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Dshamir

backend/src/lib/credits.ts

@@ -0,0 +1,43 @@
+import { prisma } from "./prisma";
+import { logger } from "./logger";
+
+const MONTHLY_CREDIT_LIMIT = Number(process.env.MONTHLY_CREDIT_LIMIT) || 999999;
+
+export async function checkCredits(
+  userId: string,
+): Promise<{ ok: true } | { ok: false; detail: string }> {
+  const profile = await prisma.userProfile.findUnique({
+    where: { userId },
+    select: { messageCreditsUsed: true, creditsResetDate: true },
+  });
+  if (!profile) return { ok: true };
+
+  if (profile.creditsResetDate && new Date() > new Date(profile.creditsResetDate)) {
+    const creditsResetDate = new Date();
+    creditsResetDate.setDate(creditsResetDate.getDate() + 30);
+    await prisma.userProfile.update({
+      where: { userId },
+      data: { messageCreditsUsed: 0, creditsResetDate },
+    });
+    return { ok: true };
+  }
+
+  if ((profile.messageCreditsUsed ?? 0) >= MONTHLY_CREDIT_LIMIT) {
+    return {
+      ok: false,
+      detail: "Monthly message credit limit reached. Please upgrade or wait for reset.",
+    };
+  }
+  return { ok: true };
+}
+
+export async function incrementCredits(userId: string): Promise<void> {
+  try {
+    await prisma.userProfile.updateMany({
+      where: { userId },
+      data: { messageCreditsUsed: { increment: 1 } },
+    });
+  } catch (err) {
+    logger.warn({ err, userId }, "[credits] failed to increment credits");
+  }
+}

backend/src/routes/chat.ts

@@ -16,6 +16,7 @@ import { checkProjectAccess } from "../lib/access";
 import { logger } from "../lib/logger";
 import { auditLog } from "../lib/audit";
 import { withStreamTimeout, StreamTimeoutError } from "../lib/streamTimeout";
+import { checkCredits, incrementCredits } from "../lib/credits";
 
 export const chatRouter = Router();
 
@@ -473,6 +474,11 @@ chatRouter.post("/", requireAuth, async (req, res) => {
 
   const workflowStore = await buildWorkflowStore(userId, userEmail);
 
+  const creditCheck = await checkCredits(userId);
+  if (!creditCheck.ok) {
+    return void res.status(429).json({ detail: creditCheck.detail });
+  }
+
   devLog("[chat/stream] starting LLM stream", {
     apiMessageCount: apiMessages.length,
     docCount: Object.keys(docIndex).length,
@@ -527,6 +533,8 @@ chatRouter.post("/", requireAuth, async (req, res) => {
         data: { title: lastUser.content.slice(0, 120) },
       });
     }
+
+    await incrementCredits(userId);
   } catch (err) {
     if (err instanceof StreamTimeoutError) {
       logger.warn({ chatId }, "[chat/stream] LLM stream timed out");

backend/src/routes/projectChat.ts

@@ -18,6 +18,7 @@ import { logger } from "../lib/logger";
 import { withStreamTimeout, StreamTimeoutError } from "../lib/streamTimeout";
 import { validate } from "../lib/validation";
 import { zodProjectChatBody } from "../lib/validation/common";
+import { checkCredits, incrementCredits } from "../lib/credits";
 
 const PROJECT_SYSTEM_PROMPT_EXTRA = `PROJECT CONTEXT:
 You are operating within a project folder that contains a collection of legal documents the user has organised for a single matter. The user's questions will usually refer to one or more documents in this project — your job is to find the relevant files to work on. Use list_documents to see what is available and fetch_documents / read_document to pull in any documents you need before answering.
@@ -122,6 +123,11 @@ projectChatRouter.post("/", validate(zodProjectChatBody), requireAuth, async (re
 
   const workflowStore = await buildWorkflowStore(userId, userEmail);
 
+  const creditCheck = await checkCredits(userId);
+  if (!creditCheck.ok) {
+    return void res.status(429).json({ detail: creditCheck.detail });
+  }
+
   res.setHeader("Content-Type", "text/event-stream");
   res.setHeader("Cache-Control", "no-cache");
   res.setHeader("Connection", "keep-alive");
@@ -166,6 +172,8 @@ projectChatRouter.post("/", validate(zodProjectChatBody), requireAuth, async (re
         data: { title: lastUser.content.slice(0, 120) },
       });
     }
+
+    await incrementCredits(userId);
   } catch (err) {
     if (err instanceof StreamTimeoutError) {
       logger.warn({ chatId }, "[project-chat/stream] LLM stream timed out");