feat(core-api): harden signed urls and llm rate limits

backend/core-api/src/middleware/error-handler.js

@@ -11,6 +11,9 @@ export function notFoundHandler(req, res) {
 
 export function errorHandler(error, req, res, _next) {
   const envelope = toErrorEnvelope(error, req.requestId);
+  if (envelope.status === 429 && envelope.body.details?.retryAfterSeconds) {
+    res.set('Retry-After', String(envelope.body.details.retryAfterSeconds));
+  }
   if (req.log) {
     req.log.error(
       {

backend/core-api/src/routes/core.js

@@ -6,9 +6,11 @@ import { requireAuth, requirePolicy } from '../middleware/auth.js';
 import { createSignedUrlSchema } from '../contracts/core/create-signed-url.js';
 import { invokeLlmSchema } from '../contracts/core/invoke-llm.js';
 import { invokeVertexModel } from '../services/llm.js';
-import { generateReadSignedUrl, uploadToGcs } from '../services/storage.js';
+import { checkLlmRateLimit } from '../services/llm-rate-limit.js';
+import { generateReadSignedUrl, uploadToGcs, validateFileUriAccess } from '../services/storage.js';
 
 const DEFAULT_MAX_FILE_BYTES = 10 * 1024 * 1024;
+const DEFAULT_MAX_SIGNED_URL_SECONDS = 900;
 const ALLOWED_FILE_TYPES = new Set(['application/pdf', 'image/jpeg', 'image/jpg', 'image/png']);
 
 const upload = multer({
@@ -105,10 +107,25 @@ async function handleCreateSignedUrl(req, res, next) {
   try {
     const payload = parseBody(createSignedUrlSchema, req.body || {});
     const expiresInSeconds = payload.expiresInSeconds || 300;
+    const maxSignedUrlSeconds = Number.parseInt(
+      process.env.MAX_SIGNED_URL_SECONDS || `${DEFAULT_MAX_SIGNED_URL_SECONDS}`,
+      10
+    );
+    if (expiresInSeconds > maxSignedUrlSeconds) {
+      throw new AppError('VALIDATION_ERROR', `expiresInSeconds must be <= ${maxSignedUrlSeconds}`, 400);
+    }
+
     const signed = useMockSignedUrl()
-      ? mockSignedUrl(payload.fileUri, expiresInSeconds)
+      ? (() => {
+          validateFileUriAccess({
+            fileUri: payload.fileUri,
+            actorUid: req.actor.uid,
+          });
+          return mockSignedUrl(payload.fileUri, expiresInSeconds);
+        })()
       : await generateReadSignedUrl({
           fileUri: payload.fileUri,
+          actorUid: req.actor.uid,
           expiresInSeconds,
         });
 
@@ -124,6 +141,12 @@ async function handleCreateSignedUrl(req, res, next) {
 async function handleInvokeLlm(req, res, next) {
   try {
     const payload = parseBody(invokeLlmSchema, req.body || {});
+    const rateLimit = checkLlmRateLimit({ uid: req.actor.uid });
+    if (!rateLimit.allowed) {
+      throw new AppError('RATE_LIMITED', 'Too many model requests. Please retry shortly.', 429, {
+        retryAfterSeconds: rateLimit.retryAfterSeconds,
+      });
+    }
 
     const startedAt = Date.now();
     if (process.env.LLM_MOCK === 'false') {

backend/core-api/src/services/llm-rate-limit.js

@@ -0,0 +1,41 @@
+const counters = new Map();
+
+function currentWindowKey(now = Date.now()) {
+  return Math.floor(now / 60000);
+}
+
+function perMinuteLimit() {
+  return Number.parseInt(process.env.LLM_RATE_LIMIT_PER_MINUTE || '20', 10);
+}
+
+export function checkLlmRateLimit({ uid, now = Date.now() }) {
+  const limit = perMinuteLimit();
+  if (!Number.isFinite(limit) || limit <= 0) {
+    return { allowed: true, remaining: null, retryAfterSeconds: 0 };
+  }
+
+  const windowKey = currentWindowKey(now);
+  const record = counters.get(uid);
+
+  if (!record || record.windowKey !== windowKey) {
+    counters.set(uid, { windowKey, count: 1 });
+    return { allowed: true, remaining: limit - 1, retryAfterSeconds: 0 };
+  }
+
+  if (record.count >= limit) {
+    const retryAfterSeconds = (windowKey + 1) * 60 - Math.floor(now / 1000);
+    return {
+      allowed: false,
+      remaining: 0,
+      retryAfterSeconds: Math.max(1, retryAfterSeconds),
+    };
+  }
+
+  record.count += 1;
+  counters.set(uid, record);
+  return { allowed: true, remaining: limit - record.count, retryAfterSeconds: 0 };
+}
+
+export function __resetLlmRateLimitForTests() {
+  counters.clear();
+}

backend/core-api/src/services/storage.js

@@ -3,7 +3,7 @@ import { AppError } from '../lib/errors.js';
 
 const storage = new Storage();
 
-function parseGsUri(fileUri) {
+export function parseGsUri(fileUri) {
   if (!fileUri.startsWith('gs://')) {
     throw new AppError('VALIDATION_ERROR', 'fileUri must start with gs://', 400);
   }
@@ -27,6 +27,20 @@ function allowedBuckets() {
   ]);
 }
 
+export function validateFileUriAccess({ fileUri, actorUid }) {
+  const { bucket, path } = parseGsUri(fileUri);
+  if (!allowedBuckets().has(bucket)) {
+    throw new AppError('FORBIDDEN', `Bucket not allowed for signing: ${bucket}`, 403);
+  }
+
+  const ownedPrefix = `uploads/${actorUid}/`;
+  if (!path.startsWith(ownedPrefix)) {
+    throw new AppError('FORBIDDEN', 'Cannot sign URL for another user path', 403);
+  }
+
+  return { bucket, path };
+}
+
 export async function uploadToGcs({ bucket, objectPath, contentType, buffer }) {
   const file = storage.bucket(bucket).file(objectPath);
   await file.save(buffer, {
@@ -38,13 +52,14 @@ export async function uploadToGcs({ bucket, objectPath, contentType, buffer }) {
   });
 }
 
-export async function generateReadSignedUrl({ fileUri, expiresInSeconds }) {
-  const { bucket, path } = parseGsUri(fileUri);
-  if (!allowedBuckets().has(bucket)) {
-    throw new AppError('FORBIDDEN', `Bucket not allowed for signing: ${bucket}`, 403);
+export async function generateReadSignedUrl({ fileUri, actorUid, expiresInSeconds }) {
+  const { bucket, path } = validateFileUriAccess({ fileUri, actorUid });
+  const file = storage.bucket(bucket).file(path);
+  const [exists] = await file.exists();
+  if (!exists) {
+    throw new AppError('NOT_FOUND', 'File not found for signed URL', 404, { fileUri });
   }
 
-  const file = storage.bucket(bucket).file(path);
   const expiresAtMs = Date.now() + expiresInSeconds * 1000;
   const [signedUrl] = await file.getSignedUrl({
     version: 'v4',