diff --git a/AGENTS.md b/AGENTS.md
index 4844073..f53fc1c 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -14,6 +14,7 @@
 - Use `checkProjectAccess()` / `checkWorkspaceAccess()` for authorization instead of ad-hoc role checks.
 - For API responses, use `successResponse` / `apiErrors` from `@/lib/api-response`.
 - Keep API and UI imports on `@/` aliases when available.
+- In Prisma raw SQL, use `$executeRaw` for statements that return no rows (e.g. `pg_advisory_xact_lock`). Using `$queryRaw` on void-returning functions causes a Prisma deserialization error (`Failed to deserialize column of type 'void'`).
 
 ## Important locations
 - Custom SQL managed by Prisma migrations: `prisma/migrations/*/migration.sql`.
diff --git a/app/(dashboard)/settings/settings-page-client.tsx b/app/(dashboard)/settings/settings-page-client.tsx
index 54bfee2..27fdaea 100644
--- a/app/(dashboard)/settings/settings-page-client.tsx
+++ b/app/(dashboard)/settings/settings-page-client.tsx
@@ -1,7 +1,7 @@
 'use client';
 
 import { useState, useEffect, useCallback } from 'react';
-import { Bell, Send, Mail, CheckCircle2, AlertCircle, Loader2, Globe, CreditCard } from 'lucide-react';
+import { Bell, Send, Mail, CheckCircle2, AlertCircle, Loader2, Globe, CreditCard, HardDrive } from 'lucide-react';
 import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
 import { Label } from '@/components/ui/label';
@@ -9,6 +9,7 @@ import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/com
 import { Separator } from '@/components/ui/separator';
 import { Skeleton } from '@/components/ui/skeleton';
 import { Badge } from '@/components/ui/badge';
+import { Progress } from '@/components/ui/progress';
 import {
   Select,
   SelectContent,
@@ -61,6 +62,20 @@ interface BillingOverview {
   };
 }
 
+interface StorageInfo {
+  usedBytes: string;
+  limitBytes: string;
+  percentage: number;
+}
+
+function formatBytes(bytesStr: string): string {
+  const bytes = Number(bytesStr);
+  if (bytes < 1024) return `${bytes} B`;
+  if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`;
+  if (bytes < 1024 * 1024 * 1024) return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
+  return `${(bytes / (1024 * 1024 * 1024)).toFixed(2)} GB`;
+}
+
 function ToggleButton({
   enabled,
   onToggle,
@@ -124,6 +139,8 @@ export default function SettingsPage({ billingOnly = false }: { billingOnly?: bo
   const [billing, setBilling] = useState<BillingOverview | null>(null);
   const [billingLoading, setBillingLoading] = useState(true);
   const [billingAction, setBillingAction] = useState<'checkout' | 'portal' | null>(null);
+  const [storageInfo, setStorageInfo] = useState<StorageInfo | null>(null);
+  const [storageLoading, setStorageLoading] = useState(true);
   const [message, setMessage] = useState<{ type: 'success' | 'error'; text: string } | null>(null);
 
   // Form state for Telegram chat ID (separate from saved settings for editing)
@@ -136,9 +153,10 @@ export default function SettingsPage({ billingOnly = false }: { billingOnly?: bo
   useEffect(() => {
     async function fetchSettings() {
       try {
-        const [settingsRes, billingRes] = await Promise.all([
+        const [settingsRes, billingRes, storageRes] = await Promise.all([
           fetch('/api/settings/notifications'),
           fetch('/api/billing'),
+          fetch('/api/settings/storage'),
         ]);
 
         if (settingsRes.ok) {
@@ -151,11 +169,17 @@ export default function SettingsPage({ billingOnly = false }: { billingOnly?: bo
           const data = await billingRes.json();
           setBilling(data.data);
         }
+
+        if (storageRes.ok) {
+          const data = await storageRes.json();
+          setStorageInfo(data.data);
+        }
       } catch {
         console.error('Failed to fetch settings');
       } finally {
         setLoading(false);
         setBillingLoading(false);
+        setStorageLoading(false);
       }
     }
     fetchSettings();
@@ -448,6 +472,62 @@ export default function SettingsPage({ billingOnly = false }: { billingOnly?: bo
         </CardContent>
       </Card>
 
+      {billing?.subscription.hasBillingAccess && (
+      <Card className="mb-6">
+        <CardHeader>
+          <CardTitle className="flex items-center gap-2">
+            <HardDrive className="h-5 w-5" />
+            Storage
+          </CardTitle>
+          <CardDescription>
+            Combined usage across video files and media attachments (200 GB limit)
+          </CardDescription>
+        </CardHeader>
+        <CardContent className="space-y-3">
+          {storageLoading || !storageInfo ? (
+            <div className="space-y-2">
+              <Skeleton className="h-4 w-48" />
+              <Skeleton className="h-2 w-full rounded-full" />
+            </div>
+          ) : (
+            <>
+              <div className="flex items-center justify-between text-sm">
+                <span className="text-muted-foreground">
+                  {formatBytes(storageInfo.usedBytes)} used of {formatBytes(storageInfo.limitBytes)}
+                </span>
+                <span
+                  className={
+                    storageInfo.percentage >= 90
+                      ? 'text-destructive font-medium'
+                      : storageInfo.percentage >= 75
+                        ? 'text-amber-600 dark:text-amber-400 font-medium'
+                        : 'text-muted-foreground'
+                  }
+                >
+                  {storageInfo.percentage < 0.1 ? '<0.1%' : `${storageInfo.percentage.toFixed(1)}%`}
+                </span>
+              </div>
+              <Progress
+                value={storageInfo.percentage}
+                className={
+                  storageInfo.percentage >= 90
+                    ? '[&>div]:bg-destructive'
+                    : storageInfo.percentage >= 75
+                      ? '[&>div]:bg-amber-500'
+                      : ''
+                }
+              />
+              {storageInfo.percentage >= 90 && (
+                <p className="text-xs text-destructive">
+                  Storage is almost full. Delete unused files or contact support.
+                </p>
+              )}
+            </>
+          )}
+        </CardContent>
+      </Card>
+      )}
+
       {!billingOnly && (
         <>
       {/* Event Subscriptions */}
diff --git a/app/api/comments/[commentId]/route.ts b/app/api/comments/[commentId]/route.ts
index 089bddc..d35333c 100644
--- a/app/api/comments/[commentId]/route.ts
+++ b/app/api/comments/[commentId]/route.ts
@@ -189,6 +189,9 @@ export async function PATCH(request: NextRequest, { params }: RouteParams) {
             if (annotationData === null) {
                 updateData.annotationData = null;
             } else {
+                if (!Array.isArray(annotationData)) {
+                    return apiErrors.badRequest('annotationData must be an array of valid stroke objects');
+                }
                 const validStrokes = validateAnnotationStrokes(annotationData);
                 if (validStrokes === null) {
                     return apiErrors.badRequest('annotationData must be an array of valid stroke objects');
diff --git a/app/api/projects/[projectId]/videos/bunny-init/route.ts b/app/api/projects/[projectId]/videos/bunny-init/route.ts
index 35cab0d..624c8df 100644
--- a/app/api/projects/[projectId]/videos/bunny-init/route.ts
+++ b/app/api/projects/[projectId]/videos/bunny-init/route.ts
@@ -8,13 +8,14 @@ import { cleanupBunnyStreamVideos } from '@/lib/bunny-stream-cleanup';
 import { createBunnyUploadToken, verifyBunnyUploadToken } from '@/lib/bunny-upload-token';
 import { isBunnyUploadsFeatureEnabled } from '@/lib/feature-flags';
 import { logError } from '@/lib/logger';
+import { enforceStorageQuota } from '@/lib/storage-quota';
 
 type RouteParams = { params: Promise<{ projectId: string }> };
 
 async function getProjectWithEditAccess(projectId: string, userId: string) {
     const project = await db.project.findUnique({
         where: { id: projectId },
-        select: { id: true, name: true, ownerId: true, workspaceId: true, visibility: true },
+        select: { id: true, name: true, ownerId: true, workspaceId: true, visibility: true, workspace: { select: { ownerId: true } } },
     });
 
     if (!project) return null;
@@ -56,6 +57,9 @@ export async function POST(request: NextRequest, { params }: RouteParams) {
             return apiErrors.badRequest('Direct uploads are disabled by this host');
         }
 
+        const quotaError = await enforceStorageQuota(project.workspace.ownerId, BigInt(0));
+        if (quotaError) return quotaError;
+
         const apiKey = process.env.BUNNY_STREAM_API_KEY;
         const libraryId = process.env.BUNNY_STREAM_LIBRARY_ID || process.env.NEXT_PUBLIC_BUNNY_STREAM_LIBRARY_ID;
 
diff --git a/app/api/settings/storage/route.ts b/app/api/settings/storage/route.ts
new file mode 100644
index 0000000..c057a27
--- /dev/null
+++ b/app/api/settings/storage/route.ts
@@ -0,0 +1,40 @@
+import { auth } from '@/lib/auth';
+import { apiErrors, successResponse, withCacheControl } from '@/lib/api-response';
+import { getUserStorageInfo } from '@/lib/storage-quota';
+import { hasBillingAccess } from '@/lib/billing';
+import { db } from '@/lib/db';
+
+// GET /api/settings/storage
+export async function GET() {
+  const session = await auth();
+  if (!session?.user?.id) {
+    return apiErrors.unauthorized();
+  }
+
+  // Only users with active billing (or on a self-hosted instance where billing
+  // is disabled) should be able to enumerate their storage breakdown.
+  const user = await db.user.findUnique({
+    where: { id: session.user.id },
+    select: {
+      subscriptionStatus: true,
+      trialEndsAt: true,
+      stripeCurrentPeriodEnd: true,
+      billingAccessEndedAt: true,
+    },
+  });
+
+  if (!user || !hasBillingAccess(user)) {
+    return apiErrors.forbidden();
+  }
+
+  const info = await getUserStorageInfo(session.user.id);
+
+  const response = successResponse({
+    usedBytes: info.usedBytes.toString(),
+    limitBytes: info.limitBytes.toString(),
+    percentage: info.percentage,
+  });
+
+  // Cache for 60s — stale data is acceptable for a usage meter
+  return withCacheControl(response, 'private, max-age=60');
+}
diff --git a/app/api/upload/audio/route.ts b/app/api/upload/audio/route.ts
index cc8631e..8278ea3 100644
--- a/app/api/upload/audio/route.ts
+++ b/app/api/upload/audio/route.ts
@@ -13,6 +13,7 @@ import {
   enforceGuestUploadQuota,
   verifyGuestUploadToken,
 } from '@/lib/guest-upload-token';
+import { reserveStorageQuota, releaseStorageReservation } from '@/lib/storage-quota';
 import { logError } from '@/lib/logger';
 
 const MAX_FILE_SIZE = 10 * 1024 * 1024; // 10MB
@@ -118,7 +119,11 @@ export async function POST(request: NextRequest) {
     const safeVideoId = videoId.trim();
     const video = await db.video.findUnique({
       where: { id: safeVideoId },
-      include: { project: true },
+      include: {
+        project: {
+          include: { workspace: { select: { ownerId: true } } },
+        },
+      },
     });
     if (!video) {
       return apiErrors.notFound('Video');
@@ -170,11 +175,20 @@ export async function POST(request: NextRequest) {
       return apiErrors.badRequest('File too large. Maximum size is 10MB.');
     }
 
+    // Enforce per-user storage quota before uploading.
+    // All paths use the advisory-locked reservation so concurrent uploads always
+    // see each other's in-flight sizes, eliminating the TOCTOU race.
+    const workspaceOwnerId = video.project.workspace.ownerId;
+    const reserveResult = await reserveStorageQuota(workspaceOwnerId, BigInt(file.size));
+    if ('error' in reserveResult) return reserveResult.error;
+    const reservationId = reserveResult.reservationId;
+
     // Normalize content type: strip codec params, then resolve aliases
     const rawContentType = file.type || 'audio/webm';
     const strippedType = rawContentType.split(';')[0].trim().toLowerCase();
     const contentType = MIME_ALIASES[strippedType] ?? strippedType;
     if (!ALLOWED_TYPES.has(contentType)) {
+      await releaseStorageReservation(reservationId);
       return apiErrors.badRequest(`Unsupported audio format: ${rawContentType}`);
     }
 
@@ -191,26 +205,33 @@ export async function POST(request: NextRequest) {
 
     // Validate file content against magic bytes — rejects HTML/scripts masquerading as audio
     if (isHtmlContent(buffer)) {
+      await releaseStorageReservation(reservationId);
       return apiErrors.badRequest('File content does not match an audio format');
     }
     if (!hasValidAudioMagicBytes(buffer.slice(0, 16), contentType)) {
+      await releaseStorageReservation(reservationId);
       return apiErrors.badRequest('File content does not match the declared audio format');
     }
 
-    // Upload to R2
-    await r2Client.send(
-      new PutObjectCommand({
-        Bucket: R2_BUCKET_NAME,
-        Key: key,
-        Body: buffer,
-        ContentType: contentType,
-      })
-    );
+    try {
+      // Upload to R2
+      await r2Client.send(
+        new PutObjectCommand({
+          Bucket: R2_BUCKET_NAME,
+          Key: key,
+          Body: buffer,
+          ContentType: contentType,
+        })
+      );
+    } catch (uploadError) {
+      await releaseStorageReservation(reservationId);
+      throw uploadError;
+    }
 
     // Return the URL through our proxy endpoint
     const voiceUrl = `/api/upload/audio/${filename}`;
 
-    const response = successResponse({ url: voiceUrl }, 201);
+    const response = successResponse({ url: voiceUrl, reservationId }, 201);
     return withCacheControl(response, 'private, no-store');
   } catch (error) {
     logError('Error uploading audio:', error);
diff --git a/app/api/upload/image/route.ts b/app/api/upload/image/route.ts
index 9803e6b..82d2f15 100644
--- a/app/api/upload/image/route.ts
+++ b/app/api/upload/image/route.ts
@@ -20,6 +20,7 @@ import {
     verifyGuestUploadToken,
 } from '@/lib/guest-upload-token';
 import { logError } from '@/lib/logger';
+import { reserveStorageQuota, releaseStorageReservation } from '@/lib/storage-quota';
 
 const MAX_FILE_SIZE = 10 * 1024 * 1024; // 10MB
 const MAX_MULTIPART_BODY_SIZE = MAX_FILE_SIZE + (512 * 1024); // file + multipart overhead
@@ -64,7 +65,11 @@ export async function POST(request: NextRequest) {
         const safeVideoId = videoId.trim();
         const video = await db.video.findUnique({
             where: { id: safeVideoId },
-            include: { project: true },
+            include: {
+                project: {
+                    include: { workspace: { select: { ownerId: true } } },
+                },
+            },
         });
         if (!video) {
             return apiErrors.notFound('Video');
@@ -116,9 +121,18 @@ export async function POST(request: NextRequest) {
             return apiErrors.badRequest('File too large. Maximum size is 10MB.');
         }
 
+        // Enforce per-user storage quota before uploading.
+        // All paths use the advisory-locked reservation so concurrent uploads always
+        // see each other's in-flight sizes, eliminating the TOCTOU race.
+        const workspaceOwnerId = video.project.workspace.ownerId;
+        const reserveResult = await reserveStorageQuota(workspaceOwnerId, BigInt(file.size));
+        if ('error' in reserveResult) return reserveResult.error;
+        const reservationId = reserveResult.reservationId;
+
         // Check content type
         const normalizedMime = normalizeImageMime(file.type);
         if (normalizedMime && !isAllowedImageType(normalizedMime)) {
+            await releaseStorageReservation(reservationId);
             return apiErrors.badRequest(`Unsupported image format: ${file.type}`);
         }
 
@@ -127,6 +141,7 @@ export async function POST(request: NextRequest) {
         const buffer = Buffer.from(arrayBuffer);
         const detectedMime = detectImageMime(buffer);
         if (!detectedMime) {
+            await releaseStorageReservation(reservationId);
             return apiErrors.badRequest('Uploaded file content does not match an allowed image type');
         }
 
@@ -135,21 +150,26 @@ export async function POST(request: NextRequest) {
         const filename = `${randomUUID()}.${ext}`;
         const key = `images/${filename}`;
 
-        // Upload to R2
-        await r2Client.send(
-            new PutObjectCommand({
-                Bucket: R2_BUCKET_NAME,
-                Key: key,
-                Body: buffer,
-                ContentType: detectedMime,
-            })
-        );
+        try {
+            // Upload to R2
+            await r2Client.send(
+                new PutObjectCommand({
+                    Bucket: R2_BUCKET_NAME,
+                    Key: key,
+                    Body: buffer,
+                    ContentType: detectedMime,
+                })
+            );
+        } catch (uploadError) {
+            await releaseStorageReservation(reservationId);
+            throw uploadError;
+        }
 
         // Return the URL through our proxy endpoint
         const imageUrl = `/api/upload/image/${filename}`;
 
-        const response = successResponse({ url: imageUrl }, 201);
-        return withCacheControl(response, 'public, max-age=31536000, immutable');
+        const response = successResponse({ url: imageUrl, reservationId }, 201);
+        return withCacheControl(response, 'private, no-store');
     } catch (error) {
         logError('Error uploading image:', error);
         return apiErrors.internalError('Failed to upload image');
diff --git a/app/api/versions/[versionId]/comments/route.ts b/app/api/versions/[versionId]/comments/route.ts
index d2da94c..94449dd 100644
--- a/app/api/versions/[versionId]/comments/route.ts
+++ b/app/api/versions/[versionId]/comments/route.ts
@@ -9,18 +9,21 @@ import { getShareSessionFromRequest } from '@/lib/share-session';
 import { HeadObjectCommand } from '@aws-sdk/client-s3';
 import { r2Client, R2_BUCKET_NAME } from '@/lib/r2';
 import { ensureGuestIdentityFromRequest, getGuestIdentityFromRequest, setGuestIdentityCookie } from '@/lib/guest-identity';
-import { extractImageFileNameFromProxyUrl, sanitizeAssetDisplayName } from '@/lib/video-assets';
+import { extractImageFileNameFromProxyUrl, extractAudioFileNameFromProxyUrl, sanitizeAssetDisplayName } from '@/lib/video-assets';
 import { validateAnnotationStrokes } from '@/lib/validation';
 import { logError } from '@/lib/logger';
+import { reserveStorageQuota, releaseStorageReservation } from '@/lib/storage-quota';
 
 type RouteParams = { params: Promise<{ versionId: string }> };
 const SAFE_IMAGE_PATH = /^\/api\/upload\/image\/[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}\.[a-z0-9]+$/i;
 const SAFE_AUDIO_PATH = /^\/api\/upload\/audio\/[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}\.[a-z0-9]+$/i;
 const UNATTACHED_UPLOAD_TTL_MS = 15 * 60 * 1000;
 
-async function isFreshAttachment(url: string, kind: 'audio' | 'image'): Promise<boolean> {
+type AttachmentCheck = { isFresh: boolean; sizeBytes: bigint };
+
+async function isFreshAttachment(url: string, kind: 'audio' | 'image'): Promise<AttachmentCheck> {
     const prefix = kind === 'audio' ? '/api/upload/audio/' : '/api/upload/image/';
-    if (!url.startsWith(prefix)) return false;
+    if (!url.startsWith(prefix)) return { isFresh: false, sizeBytes: BigInt(0) };
 
     const filename = url.slice(prefix.length);
     const key = kind === 'audio' ? `voice/${filename}` : `images/${filename}`;
@@ -32,10 +35,11 @@ async function isFreshAttachment(url: string, kind: 'audio' | 'image'): Promise<
                 Key: key,
             })
         );
-        if (!head.LastModified) return false;
-        return Date.now() - head.LastModified.getTime() <= UNATTACHED_UPLOAD_TTL_MS;
+        if (!head.LastModified) return { isFresh: false, sizeBytes: BigInt(0) };
+        const isFresh = Date.now() - head.LastModified.getTime() <= UNATTACHED_UPLOAD_TTL_MS;
+        return { isFresh, sizeBytes: BigInt(head.ContentLength ?? 0) };
     } catch {
-        return false;
+        return { isFresh: false, sizeBytes: BigInt(0) };
     }
 }
 
@@ -188,6 +192,7 @@ export async function GET(request: NextRequest, { params }: RouteParams) {
 
 // POST /api/versions/[versionId]/comments
 export async function POST(request: NextRequest, { params }: RouteParams) {
+    let attachmentReservationId: string | null = null;
     try {
         const limited = await rateLimit(request, 'comment');
         if (limited) return limited;
@@ -275,8 +280,12 @@ export async function POST(request: NextRequest, { params }: RouteParams) {
 
         // Validate annotation data structure to prevent prototype pollution and stored XSS.
         // Reject anything that is not a well-formed array of AnnotationStroke objects.
+        // The HTTP body is already JSON-parsed by Next.js; double-encoded strings are rejected.
         let serializedAnnotationData: string | null = null;
         if (annotationData !== undefined && annotationData !== null) {
+            if (!Array.isArray(annotationData)) {
+                return apiErrors.badRequest('annotationData must be an array of valid stroke objects');
+            }
             const validStrokes = validateAnnotationStrokes(annotationData);
             if (validStrokes === null) {
                 return apiErrors.badRequest('annotationData must be an array of valid stroke objects');
@@ -317,21 +326,45 @@ export async function POST(request: NextRequest, { params }: RouteParams) {
         if (voiceUrl && !SAFE_AUDIO_PATH.test(voiceUrl)) {
             return apiErrors.badRequest('Voice URL must reference an uploaded audio file');
         }
-        if (voiceUrl && !(await isFreshAttachment(voiceUrl, 'audio'))) {
-            return apiErrors.badRequest('Voice upload expired. Please upload again.');
+        let voiceSizeBytes = BigInt(0);
+        if (voiceUrl) {
+            const voiceCheck = await isFreshAttachment(voiceUrl, 'audio');
+            if (!voiceCheck.isFresh) {
+                return apiErrors.badRequest('Voice upload expired. Please upload again.');
+            }
+            voiceSizeBytes = voiceCheck.sizeBytes;
         }
 
         if (imageUrl && !SAFE_IMAGE_PATH.test(imageUrl)) {
             return apiErrors.badRequest('Image URL must reference an uploaded image file');
         }
-        if (imageUrl && !(await isFreshAttachment(imageUrl, 'image'))) {
-            return apiErrors.badRequest('Image upload expired. Please upload again.');
+        let imageSizeBytes = BigInt(0);
+        if (imageUrl) {
+            const imageCheck = await isFreshAttachment(imageUrl, 'image');
+            if (!imageCheck.isFresh) {
+                return apiErrors.badRequest('Image upload expired. Please upload again.');
+            }
+            imageSizeBytes = imageCheck.sizeBytes;
         }
 
         const guestIdentity = isGuest ? ensureGuestIdentityFromRequest(request) : null;
 
-        // Use a transaction to create both comment and asset (if image is attached)
+        // Enforce per-workspace storage quota for any R2 attachments on this comment.
+        // Uses the advisory-locked reservation path so concurrent comment submissions
+        // see each other's in-flight sizes, eliminating the TOCTOU race.
+        const totalAttachmentBytes = voiceSizeBytes + imageSizeBytes;
+        if (totalAttachmentBytes > BigInt(0)) {
+            const reserveResult = await reserveStorageQuota(project.workspace.ownerId, totalAttachmentBytes);
+            if ('error' in reserveResult) return reserveResult.error;
+            attachmentReservationId = reserveResult.reservationId;
+        }
+
+        // Use a transaction to create both the comment and any asset rows atomically.
+        // Consume the reservation inside the transaction so quota is never double-counted.
         const result = await db.$transaction(async (tx) => {
+            if (attachmentReservationId) {
+                await tx.uploadReservation.deleteMany({ where: { id: attachmentReservationId, billedUserId: project.workspace.ownerId } });
+            }
             const comment = await tx.comment.create({
                 data: {
                     content: content?.trim() || null,
@@ -375,6 +408,29 @@ export async function POST(request: NextRequest, { params }: RouteParams) {
                         displayName,
                         sourceUrl: imageUrl,
                         thumbnailUrl: imageUrl,
+                        sizeBytes: imageSizeBytes,
+                        uploadedByUserId: session?.user?.id || null,
+                        uploadedByGuestIdentityId: isGuest ? guestIdentity?.identityId ?? null : null,
+                        uploadedByGuestName: isGuest ? safeGuestName : null,
+                        billedUserId: project.workspace.ownerId,
+                    },
+                });
+            }
+
+            // If a voice recording was attached, also track it in the assets pane
+            if (voiceUrl) {
+                const fileName = extractAudioFileNameFromProxyUrl(voiceUrl);
+                const displayName = sanitizeAssetDisplayName(null, fileName || 'Voice Comment');
+                const safeGuestName = sanitizeAssetDisplayName(guestName, 'Guest').slice(0, 80);
+
+                await tx.videoAsset.create({
+                    data: {
+                        videoId: version.video.id,
+                        kind: 'AUDIO',
+                        provider: 'R2_AUDIO',
+                        displayName,
+                        sourceUrl: voiceUrl,
+                        sizeBytes: voiceSizeBytes,
                         uploadedByUserId: session?.user?.id || null,
                         uploadedByGuestIdentityId: isGuest ? guestIdentity?.identityId ?? null : null,
                         uploadedByGuestName: isGuest ? safeGuestName : null,
@@ -450,6 +506,7 @@ export async function POST(request: NextRequest, { params }: RouteParams) {
         }
         return withCacheControl(response, 'private, no-store');
     } catch (error) {
+        await releaseStorageReservation(attachmentReservationId);
         logError('Error creating comment:', error);
         return apiErrors.internalError('Failed to create comment');
     }
diff --git a/app/api/videos/[videoId]/assets/bunny-init/route.ts b/app/api/videos/[videoId]/assets/bunny-init/route.ts
index df65303..d3946c8 100644
--- a/app/api/videos/[videoId]/assets/bunny-init/route.ts
+++ b/app/api/videos/[videoId]/assets/bunny-init/route.ts
@@ -14,6 +14,7 @@ import { isBunnyUploadsFeatureEnabled } from '@/lib/feature-flags';
 import { getShareSessionFromRequest } from '@/lib/share-session';
 import { getVideoAssetAccessContext, SAFE_BUNNY_VIDEO_ID } from '@/lib/video-assets';
 import { logError } from '@/lib/logger';
+import { enforceStorageQuota } from '@/lib/storage-quota';
 
 type RouteParams = { params: Promise<{ videoId: string }> };
 
@@ -36,6 +37,10 @@ export async function POST(request: NextRequest, { params }: RouteParams) {
       return apiErrors.badRequest('Direct uploads are disabled by this host');
     }
 
+    const billedUserId = context.video.project.workspace.ownerId;
+    const quotaError = await enforceStorageQuota(billedUserId, BigInt(0));
+    if (quotaError) return quotaError;
+
     const shareSession = getShareSessionFromRequest(request, context.video.id);
     if (!context.viewerUserId) {
       const quotaError = await enforceGuestUploadQuota(request, context.video.id, 'bunny', shareSession?.token ?? null);
diff --git a/app/api/videos/[videoId]/assets/route.ts b/app/api/videos/[videoId]/assets/route.ts
index 61eabd2..648658a 100644
--- a/app/api/videos/[videoId]/assets/route.ts
+++ b/app/api/videos/[videoId]/assets/route.ts
@@ -25,6 +25,13 @@ import {
   sanitizeAssetDisplayName,
 } from '@/lib/video-assets';
 import { logError } from '@/lib/logger';
+import { enforceStorageQuota, reserveStorageQuota, releaseStorageReservation, PLAN_STORAGE_LIMIT_BYTES } from '@/lib/storage-quota';
+import { getCachedUserBunnyStorage } from '@/lib/admin-stats';
+import { isStripeFeatureEnabled } from '@/lib/feature-flags';
+
+// Sentinel thrown inside a Prisma transaction when a fake reservationId is
+// supplied and the fallback quota check finds the limit would be exceeded.
+class QuotaExceededInTxError extends Error {}
 
 type RouteParams = { params: Promise<{ videoId: string }> };
 
@@ -147,35 +154,39 @@ async function fetchYouTubeTitle(videoId: string): Promise<string | null> {
   return title;
 }
 
-async function isFreshImageAttachment(url: string): Promise<boolean> {
+type AttachmentCheck = { isFresh: boolean; sizeBytes: bigint };
+
+async function isFreshImageAttachment(url: string): Promise<AttachmentCheck> {
   const key = extractImageKeyFromProxyUrl(url);
-  if (!key) return false;
+  if (!key) return { isFresh: false, sizeBytes: BigInt(0) };
 
   try {
     const head = await r2Client.send(new HeadObjectCommand({
       Bucket: R2_BUCKET_NAME,
       Key: key,
     }));
-    if (!head.LastModified) return false;
-    return Date.now() - head.LastModified.getTime() <= UNATTACHED_UPLOAD_TTL_MS;
+    if (!head.LastModified) return { isFresh: false, sizeBytes: BigInt(0) };
+    const isFresh = Date.now() - head.LastModified.getTime() <= UNATTACHED_UPLOAD_TTL_MS;
+    return { isFresh, sizeBytes: BigInt(head.ContentLength ?? 0) };
   } catch {
-    return false;
+    return { isFresh: false, sizeBytes: BigInt(0) };
   }
 }
 
-async function isFreshAudioAttachment(url: string): Promise<boolean> {
+async function isFreshAudioAttachment(url: string): Promise<AttachmentCheck> {
   const key = extractAudioKeyFromProxyUrl(url);
-  if (!key) return false;
+  if (!key) return { isFresh: false, sizeBytes: BigInt(0) };
 
   try {
     const head = await r2Client.send(new HeadObjectCommand({
       Bucket: R2_BUCKET_NAME,
       Key: key,
     }));
-    if (!head.LastModified) return false;
-    return Date.now() - head.LastModified.getTime() <= UNATTACHED_UPLOAD_TTL_MS;
+    if (!head.LastModified) return { isFresh: false, sizeBytes: BigInt(0) };
+    const isFresh = Date.now() - head.LastModified.getTime() <= UNATTACHED_UPLOAD_TTL_MS;
+    return { isFresh, sizeBytes: BigInt(head.ContentLength ?? 0) };
   } catch {
-    return false;
+    return { isFresh: false, sizeBytes: BigInt(0) };
   }
 }
 
@@ -268,6 +279,7 @@ export async function GET(request: NextRequest, { params }: RouteParams) {
 
 // POST /api/videos/[videoId]/assets
 export async function POST(request: NextRequest, { params }: RouteParams) {
+  let reservationId: string | null = null;
   try {
     const limited = await rateLimit(request, 'asset-create');
     if (limited) return limited;
@@ -293,20 +305,38 @@ export async function POST(request: NextRequest, { params }: RouteParams) {
     const guestIdentity = isGuest ? ensureGuestIdentityFromRequest(request) : null;
 
     const requestedDisplayName = typeof body?.displayName === 'string' ? body.displayName : null;
+    // Optional reservation ID created by the upload route for atomic quota accounting
+    reservationId = typeof body?.reservationId === 'string' ? body.reservationId.trim() : null;
     let displayName = '';
     let sourceUrl = '';
     let providerVideoId: string | null = null;
     let thumbnailUrl: string | null = null;
     let kind: 'IMAGE' | 'VIDEO' | 'AUDIO' = 'IMAGE';
+    let assetSizeBytes = BigInt(0);
+
+    const billedUserId = context.video.project.workspace.ownerId;
 
     if (provider === VideoAssetProvider.R2_IMAGE) {
       sourceUrl = typeof body?.sourceUrl === 'string' ? body.sourceUrl.trim() : '';
       if (!SAFE_IMAGE_PROXY_PATH.test(sourceUrl)) {
         return apiErrors.badRequest('Image URL must reference an uploaded image file');
       }
-      if (!(await isFreshImageAttachment(sourceUrl))) {
+      const imageCheck = await isFreshImageAttachment(sourceUrl);
+      if (!imageCheck.isFresh) {
         return apiErrors.badRequest('Image upload expired. Please upload again.');
       }
+      assetSizeBytes = imageCheck.sizeBytes;
+
+      // Always use the advisory-locked reservation path so concurrent uploads
+      // see each other's in-flight sizes, eliminating the TOCTOU race.  When
+      // the client already supplied a reservationId (new upload flow) the
+      // existing reservation is consumed in the transaction below.  For the
+      // backward-compat path (no reservationId) we create one here.
+      if (!reservationId) {
+        const reserveResult = await reserveStorageQuota(billedUserId, assetSizeBytes);
+        if ('error' in reserveResult) return reserveResult.error;
+        reservationId = reserveResult.reservationId;
+      }
 
       const fileName = extractImageFileNameFromProxyUrl(sourceUrl);
       displayName = sanitizeAssetDisplayName(requestedDisplayName, fileName || 'Image');
@@ -319,9 +349,18 @@ export async function POST(request: NextRequest, { params }: RouteParams) {
       if (!SAFE_AUDIO_PROXY_PATH.test(sourceUrl)) {
         return apiErrors.badRequest('Audio URL must reference an uploaded audio file');
       }
-      if (!(await isFreshAudioAttachment(sourceUrl))) {
+      const audioCheck = await isFreshAudioAttachment(sourceUrl);
+      if (!audioCheck.isFresh) {
         return apiErrors.badRequest('Audio upload expired. Please upload again.');
       }
+      assetSizeBytes = audioCheck.sizeBytes;
+
+      // Same reservation logic as R2_IMAGE above
+      if (!reservationId) {
+        const reserveResult = await reserveStorageQuota(billedUserId, assetSizeBytes);
+        if ('error' in reserveResult) return reserveResult.error;
+        reservationId = reserveResult.reservationId;
+      }
 
       const fileName = extractAudioFileNameFromProxyUrl(sourceUrl);
       displayName = sanitizeAssetDisplayName(requestedDisplayName, fileName || 'Voice Recording');
@@ -405,40 +444,100 @@ export async function POST(request: NextRequest, { params }: RouteParams) {
         }
       }
       kind = 'VIDEO';
+
+      const quotaError = await enforceStorageQuota(billedUserId, BigInt(0));
+      if (quotaError) return quotaError;
     }
 
-    const created = await db.videoAsset.create({
-      data: {
-        videoId: context.video.id,
-        kind,
-        provider,
-        displayName,
-        sourceUrl,
-        providerVideoId,
-        thumbnailUrl,
-        uploadedByUserId: context.viewerUserId,
-        uploadedByGuestIdentityId: context.viewerUserId ? null : guestIdentity?.identityId ?? null,
-        uploadedByGuestName: context.viewerUserId
-          ? null
-          : sanitizeAssetDisplayName(typeof body?.guestName === 'string' ? body.guestName : null, 'Guest'),
-        billedUserId: context.video.project.workspace.ownerId,
-      },
-      select: {
-        id: true,
-        videoId: true,
-        kind: true,
-        provider: true,
-        displayName: true,
-        sourceUrl: true,
-        providerVideoId: true,
-        thumbnailUrl: true,
-        uploadedByGuestName: true,
-        createdAt: true,
-        updatedAt: true,
-        uploadedByUser: {
-          select: { id: true, name: true, image: true },
+    // Pre-fetch Bunny storage BEFORE entering the transaction to avoid making an
+    // HTTP call while holding a DB connection open (connection-pool exhaustion
+    // risk under adversarial load). Mirrors the discipline in reserveStorageQuota.
+    // Only needed for R2 providers where the invalid-reservation fallback quota
+    // check requires Bunny usage data.
+    const preFetchedBunnyData =
+      provider === VideoAssetProvider.R2_IMAGE || provider === VideoAssetProvider.R2_AUDIO
+        ? await getCachedUserBunnyStorage()
+        : null;
+
+    // Create the VideoAsset and atomically consume the upload reservation (if any)
+    // so the spot is never double-counted.
+    const created = await db.$transaction(async (tx) => {
+      if (reservationId) {
+        // Acquire the per-user advisory lock unconditionally so both the happy path
+        // (valid reservation) and the fallback path (fake/expired reservation ID) are
+        // serialised — eliminating the TOCTOU race in the deleted.count === 0 branch.
+        await tx.$executeRaw`
+          SELECT pg_advisory_xact_lock(
+            ('x' || left(md5(${billedUserId}), 16))::bit(64)::bigint
+          )
+        `;
+        // Validate the reservation by checking it actually exists and belongs to the
+        // billed user. A client-supplied fake ID would delete 0 rows — in that case
+        // we fall back to a standard (non-locked) quota check so the bypass attempt
+        // is caught rather than silently allowed.
+        const deleted = await tx.uploadReservation.deleteMany({
+          where: { id: reservationId, billedUserId, expiresAt: { gt: new Date() } },
+        });
+        if (deleted.count === 0) {
+          // Reservation didn't exist — enforce quota the normal way inside the tx.
+          // We read inside the same transaction so the check is at least consistent
+          // with the asset insert that follows.
+          const [r2Row] = await tx.$queryRaw<[{ total: bigint }]>`
+            SELECT COALESCE(SUM(size_bytes), 0)::bigint AS total
+            FROM video_assets
+            WHERE "billedUserId" = ${billedUserId}
+              AND provider IN ('R2_IMAGE', 'R2_AUDIO')
+          `;
+          const [resRow] = await tx.$queryRaw<[{ total: bigint }]>`
+            SELECT COALESCE(SUM("sizeBytes"), 0)::bigint AS total
+            FROM upload_reservations
+            WHERE "billedUserId" = ${billedUserId}
+              AND "expiresAt" > NOW()
+          `;
+          const bunnyData = preFetchedBunnyData ?? {};
+          const totalUsed =
+            (r2Row?.total ?? BigInt(0)) +
+            (resRow?.total ?? BigInt(0)) +
+            BigInt(bunnyData[billedUserId] ?? 0);
+          if (isStripeFeatureEnabled() && totalUsed + assetSizeBytes >= PLAN_STORAGE_LIMIT_BYTES) {
+            throw new QuotaExceededInTxError();
+          }
+        }
+      }
+      return tx.videoAsset.create({
+        data: {
+          videoId: context.video.id,
+          kind,
+          provider,
+          displayName,
+          sourceUrl,
+          providerVideoId,
+          thumbnailUrl,
+          sizeBytes: assetSizeBytes,
+          uploadedByUserId: context.viewerUserId,
+          uploadedByGuestIdentityId: context.viewerUserId ? null : guestIdentity?.identityId ?? null,
+          uploadedByGuestName: context.viewerUserId
+            ? null
+            : sanitizeAssetDisplayName(typeof body?.guestName === 'string' ? body.guestName : null, 'Guest'),
+          billedUserId,
         },
-      },
+        select: {
+          id: true,
+          videoId: true,
+          kind: true,
+          provider: true,
+          displayName: true,
+          sourceUrl: true,
+          providerVideoId: true,
+          thumbnailUrl: true,
+          uploadedByGuestName: true,
+          createdAt: true,
+          updatedAt: true,
+          uploadedByUser: {
+            select: { id: true, name: true, image: true },
+          },
+        },
+      });
     });
 
     const response = successResponse(shapeAssetForViewer(
@@ -451,6 +550,10 @@ export async function POST(request: NextRequest, { params }: RouteParams) {
     }
     return withCacheControl(response, 'private, no-store');
   } catch (error) {
+    if (error instanceof QuotaExceededInTxError) {
+      return apiErrors.storageExceeded() as NextResponse;
+    }
+    await releaseStorageReservation(reservationId);
     logError('Error creating video asset:', error);
     return apiErrors.internalError('Failed to create asset');
   }
diff --git a/components/ui/progress.tsx b/components/ui/progress.tsx
new file mode 100644
index 0000000..3ae52b3
--- /dev/null
+++ b/components/ui/progress.tsx
@@ -0,0 +1,23 @@
+import { cn } from '@/lib/utils';
+
+function Progress({
+  value = 0,
+  className,
+  ...props
+}: React.ComponentProps<'div'> & { value?: number }) {
+  const clamped = Math.min(100, Math.max(0, value));
+  return (
+    <div
+      data-slot="progress"
+      className={cn('relative h-2 w-full overflow-hidden rounded-full bg-muted', className)}
+      {...props}
+    >
+      <div
+        className="h-full bg-primary transition-all"
+        style={{ width: `${clamped}%` }}
+      />
+    </div>
+  );
+}
+
+export { Progress };
diff --git a/components/video-page/assets-pane.tsx b/components/video-page/assets-pane.tsx
index 30b37a6..5c5a608 100644
--- a/components/video-page/assets-pane.tsx
+++ b/components/video-page/assets-pane.tsx
@@ -33,7 +33,7 @@ function formatTime(seconds: number): string {
 }
 
 type UploadAudioResponse = {
-  data?: { url?: string };
+  data?: { url?: string; reservationId?: string | null };
   error?: string;
 };
 
@@ -74,6 +74,7 @@ interface AssetsPaneProps {
     providerVideoId?: string;
     thumbnailUrl?: string;
     uploadToken?: string;
+    reservationId?: string | null;
   }) => Promise<VideoAsset | null>;
   deleteAsset: (assetId: string) => Promise<boolean>;
   downloadAsset: (asset: VideoAsset, preference?: 'original' | 'compressed') => Promise<void>;
@@ -303,7 +304,7 @@ export const AssetsPane = memo(function AssetsPane({
         method: 'POST',
         body: formData,
       });
-      const uploadPayload = (await uploadRes.json().catch(() => null)) as { data?: { url?: string }; error?: string } | null;
+      const uploadPayload = (await uploadRes.json().catch(() => null)) as { data?: { url?: string; reservationId?: string | null }; error?: string } | null;
       const uploadedImageUrl = uploadPayload?.data?.url;
       if (!uploadRes.ok || !uploadedImageUrl) {
         toast.error(uploadPayload?.error || 'Failed to upload image');
@@ -314,6 +315,7 @@ export const AssetsPane = memo(function AssetsPane({
         provider: 'R2_IMAGE',
         sourceUrl: uploadedImageUrl,
         displayName: imageTitle.trim() || file.name,
+        reservationId: uploadPayload?.data?.reservationId ?? null,
       });
       if (imageInputRef.current) imageInputRef.current.value = '';
       setImageTitle('');
@@ -586,6 +588,7 @@ export const AssetsPane = memo(function AssetsPane({
         provider: 'R2_AUDIO',
         sourceUrl: uploadedUrl,
         displayName: voiceTitle.trim() || fallbackName,
+        reservationId: uploadPayload?.data?.reservationId ?? null,
       });
       setVoiceTitle('');
       setAudioBlob(null);
diff --git a/components/video-page/hooks/use-comment-actions.ts b/components/video-page/hooks/use-comment-actions.ts
index b73a02d..e25f052 100644
--- a/components/video-page/hooks/use-comment-actions.ts
+++ b/components/video-page/hooks/use-comment-actions.ts
@@ -207,7 +207,7 @@ export function useCommentActions({
           ...(imageData && { imageUrl: imageData.url }),
           ...(isGuest && normalizedGuestName && { guestName: normalizedGuestName }),
           ...(selectedTagId && { tagId: selectedTagId }),
-          ...(serializedAnnotation && { annotationData: serializedAnnotation }),
+          ...(effectiveStrokes && { annotationData: effectiveStrokes }),
         }),
       });
 
@@ -830,7 +830,9 @@ export function useCommentActions({
     try {
       const body: Record<string, unknown> = { content: editText };
       if (editTagId !== undefined) body.tagId = editTagId;
-      if (finalAnnotationData !== undefined) body.annotationData = finalAnnotationData;
+      if (finalAnnotationData !== undefined) {
+        body.annotationData = finalAnnotationData !== null ? JSON.parse(finalAnnotationData) : null;
+      }
       if (isGuest && normalizedGuestName) body.guestName = normalizedGuestName;
       const res = await fetch(`/api/comments/${commentId}`, {
         method: 'PATCH',
diff --git a/components/video-page/hooks/use-video-assets.ts b/components/video-page/hooks/use-video-assets.ts
index bd726d4..f15cdc1 100644
--- a/components/video-page/hooks/use-video-assets.ts
+++ b/components/video-page/hooks/use-video-assets.ts
@@ -13,6 +13,7 @@ type CreateAssetPayload = {
   providerVideoId?: string;
   thumbnailUrl?: string;
   uploadToken?: string;
+  reservationId?: string | null;
 };
 
 interface UseVideoAssetsParams {
diff --git a/lib/admin-stats.ts b/lib/admin-stats.ts
index 3600ea3..b1b506f 100644
--- a/lib/admin-stats.ts
+++ b/lib/admin-stats.ts
@@ -7,7 +7,7 @@ import { getStripe, getStripePriceId } from '@/lib/stripe';
 import { logError } from '@/lib/logger';
 
 const BUNNY_API_BASE = 'https://video.bunnycdn.com';
-const STORAGE_CACHE_SECONDS = 600;
+const STORAGE_CACHE_SECONDS = 120;
 
 interface R2StorageSnapshot {
     fileSizes: Map<string, number>;
diff --git a/lib/api-response.ts b/lib/api-response.ts
index 0e2111c..dfeec0c 100644
--- a/lib/api-response.ts
+++ b/lib/api-response.ts
@@ -36,6 +36,7 @@ export const HttpStatus = {
   CONFLICT: 409,
   UNPROCESSABLE_ENTITY: 422,
   TOO_MANY_REQUESTS: 429,
+  INSUFFICIENT_STORAGE: 507,
   INTERNAL_SERVER_ERROR: 500,
 } as const;
 
@@ -62,6 +63,9 @@ export const ErrorCode = {
   // Server errors
   INTERNAL_ERROR: "INTERNAL_ERROR",
   SERVICE_UNAVAILABLE: "SERVICE_UNAVAILABLE",
+
+  // Storage errors
+  STORAGE_LIMIT_EXCEEDED: "STORAGE_LIMIT_EXCEEDED",
 } as const;
 
 /**
@@ -158,4 +162,7 @@ export const apiErrors = {
 
   internalError: (message = "Internal server error") =>
     errorResponse(message, HttpStatus.INTERNAL_SERVER_ERROR, ErrorCode.INTERNAL_ERROR),
+
+  storageExceeded: (message = "Storage limit exceeded. Please delete some files to free up space.") =>
+    errorResponse(message, HttpStatus.INSUFFICIENT_STORAGE, ErrorCode.STORAGE_LIMIT_EXCEEDED),
 };
diff --git a/lib/storage-quota.ts b/lib/storage-quota.ts
new file mode 100644
index 0000000..5c0fcba
--- /dev/null
+++ b/lib/storage-quota.ts
@@ -0,0 +1,176 @@
+import type { NextResponse } from 'next/server';
+import { db } from '@/lib/db';
+import { apiErrors } from '@/lib/api-response';
+import { isStripeFeatureEnabled } from '@/lib/feature-flags';
+import { getCachedUserBunnyStorage } from '@/lib/admin-stats';
+
+// 200 GB expressed in bytes
+export const PLAN_STORAGE_LIMIT_BYTES = BigInt(200) * BigInt(1024) * BigInt(1024) * BigInt(1024);
+
+// TTL for upload reservations: 30 minutes is enough for R2 image/audio uploads
+const RESERVATION_TTL_MS = 30 * 60 * 1000;
+
+// Sentinel error thrown inside a Prisma transaction to signal quota exceeded
+class QuotaExceededError extends Error {}
+
+/**
+ * Returns total bytes used by a given billed user across R2 (image + audio),
+ * Bunny Stream, and any active (non-expired) upload reservations.
+ * Uses the cached Bunny stats (10-min TTL) to avoid calling the Bunny API on
+ * every upload.
+ */
+export async function getUserTotalStorageBytes(userId: string): Promise<bigint> {
+  const [r2Rows, bunnyByUser, reservationRows] = await Promise.all([
+    db.$queryRaw<[{ total: bigint }]>`
+      SELECT COALESCE(SUM(size_bytes), 0)::bigint AS total
+      FROM video_assets
+      WHERE "billedUserId" = ${userId}
+        AND provider IN ('R2_IMAGE', 'R2_AUDIO')
+    `,
+    getCachedUserBunnyStorage(),
+    db.$queryRaw<[{ total: bigint }]>`
+      SELECT COALESCE(SUM("sizeBytes"), 0)::bigint AS total
+      FROM upload_reservations
+      WHERE "billedUserId" = ${userId}
+        AND "expiresAt" > NOW()
+    `,
+  ]);
+
+  const r2Bytes = r2Rows[0]?.total ?? BigInt(0);
+  const bunnyBytes = BigInt(bunnyByUser[userId] ?? 0);
+  const reservedBytes = reservationRows[0]?.total ?? BigInt(0);
+
+  return r2Bytes + bunnyBytes + reservedBytes;
+}
+
+/**
+ * Returns storage usage info for a user in a UI-friendly shape.
+ */
+export async function getUserStorageInfo(userId: string): Promise<{
+  usedBytes: bigint;
+  limitBytes: bigint;
+  percentage: number;
+}> {
+  const usedBytes = await getUserTotalStorageBytes(userId);
+  const limitBytes = PLAN_STORAGE_LIMIT_BYTES;
+  const percentage = limitBytes > BigInt(0)
+    ? Math.min(100, Number((usedBytes * BigInt(10000)) / limitBytes) / 100)
+    : 0;
+
+  return { usedBytes, limitBytes, percentage };
+}
+
+/**
+ * Checks whether the user can upload `incomingSizeBytes` more data.
+ *
+ * Returns a 507 response if the quota would be exceeded, or `null` if the
+ * upload is allowed. When Stripe is disabled the check is always skipped so
+ * self-hosted instances without billing still work.
+ *
+ * Uses `>=` so a user at exactly the limit cannot initiate new uploads.
+ */
+export async function enforceStorageQuota(
+  userId: string,
+  incomingSizeBytes: bigint,
+): Promise<NextResponse | null> {
+  if (!isStripeFeatureEnabled()) {
+    return null;
+  }
+
+  const usedBytes = await getUserTotalStorageBytes(userId);
+
+  if (usedBytes + incomingSizeBytes >= PLAN_STORAGE_LIMIT_BYTES) {
+    return apiErrors.storageExceeded() as NextResponse;
+  }
+
+  return null;
+}
+
+/**
+ * Atomically checks the quota and records an in-flight upload reservation.
+ *
+ * Uses a PostgreSQL advisory transaction lock (per user) so concurrent callers
+ * are serialised: the second request sees the first reservation in the sum and
+ * cannot double-book the same headroom.
+ *
+ * Returns `{ reservationId }` on success or `{ error }` (a 507 NextResponse)
+ * when the quota would be exceeded. Call `releaseStorageReservation` to delete
+ * the reservation once the paired asset is committed (or if the upload fails).
+ *
+ * When Stripe is disabled the check is skipped and `reservationId` is `null`.
+ */
+export async function reserveStorageQuota(
+  userId: string,
+  incomingSizeBytes: bigint,
+): Promise<{ reservationId: string | null } | { error: NextResponse }> {
+  if (!isStripeFeatureEnabled()) {
+    return { reservationId: null };
+  }
+
+  const expiresAt = new Date(Date.now() + RESERVATION_TTL_MS);
+
+  // Fetch Bunny storage BEFORE entering the transaction to avoid holding the
+  // advisory lock during a potentially slow/failing HTTP call on cache miss.
+  const bunnyData = await getCachedUserBunnyStorage();
+  const bunnyBytes = BigInt(bunnyData[userId] ?? 0);
+
+  try {
+    const reservationId = await db.$transaction(async (tx) => {
+      // Serialise quota checks for this user via a per-user advisory lock.
+      // Combine two 32-bit hashtext() halves into a single 64-bit bigint to
+      // eliminate the 32-bit hash-space collision risk of plain hashtext().
+      // Use $executeRaw — the function returns void which $queryRaw cannot deserialize.
+      await tx.$executeRaw`
+        SELECT pg_advisory_xact_lock(
+          ('x' || left(md5(${userId}), 16))::bit(64)::bigint
+        )
+      `;
+
+      // Read committed R2 storage under the lock
+      const [r2Row] = await tx.$queryRaw<[{ total: bigint }]>`
+        SELECT COALESCE(SUM(size_bytes), 0)::bigint AS total
+        FROM video_assets
+        WHERE "billedUserId" = ${userId}
+          AND provider IN ('R2_IMAGE', 'R2_AUDIO')
+      `;
+      const r2Bytes = r2Row?.total ?? BigInt(0);
+
+      // Read active (non-expired) reservations under the same lock
+      const [resRow] = await tx.$queryRaw<[{ total: bigint }]>`
+        SELECT COALESCE(SUM("sizeBytes"), 0)::bigint AS total
+        FROM upload_reservations
+        WHERE "billedUserId" = ${userId}
+          AND "expiresAt" > NOW()
+      `;
+      const reservedBytes = resRow?.total ?? BigInt(0);
+
+      const totalUsed = r2Bytes + reservedBytes + bunnyBytes;
+      if (totalUsed + incomingSizeBytes >= PLAN_STORAGE_LIMIT_BYTES) {
+        throw new QuotaExceededError();
+      }
+
+      const reservation = await tx.uploadReservation.create({
+        data: { billedUserId: userId, sizeBytes: incomingSizeBytes, expiresAt },
+        select: { id: true },
+      });
+
+      return reservation.id;
+    });
+
+    return { reservationId };
+  } catch (e) {
+    if (e instanceof QuotaExceededError) {
+      return { error: apiErrors.storageExceeded() as NextResponse };
+    }
+    throw e;
+  }
+}
+
+/**
+ * Deletes an upload reservation created by `reserveStorageQuota`.
+ * Safe to call with `null` (no-op) for flows where billing is disabled.
+ */
+export async function releaseStorageReservation(reservationId: string | null): Promise<void> {
+  if (!reservationId) return;
+  await db.uploadReservation.deleteMany({ where: { id: reservationId } });
+}
diff --git a/prisma/migrations/20260414120000_add_size_bytes_to_video_assets/migration.sql b/prisma/migrations/20260414120000_add_size_bytes_to_video_assets/migration.sql
new file mode 100644
index 0000000..c0e5e07
--- /dev/null
+++ b/prisma/migrations/20260414120000_add_size_bytes_to_video_assets/migration.sql
@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "video_assets" ADD COLUMN "size_bytes" BIGINT NOT NULL DEFAULT 0;
diff --git a/prisma/migrations/20260415120000_add_upload_reservations/migration.sql b/prisma/migrations/20260415120000_add_upload_reservations/migration.sql
new file mode 100644
index 0000000..d7f74c0
--- /dev/null
+++ b/prisma/migrations/20260415120000_add_upload_reservations/migration.sql
@@ -0,0 +1,13 @@
+-- CreateTable
+CREATE TABLE "upload_reservations" (
+    "id" TEXT NOT NULL,
+    "billedUserId" TEXT NOT NULL,
+    "sizeBytes" BIGINT NOT NULL,
+    "expiresAt" TIMESTAMP(3) NOT NULL,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "upload_reservations_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE INDEX "upload_reservations_billedUserId_expiresAt_idx" ON "upload_reservations"("billedUserId", "expiresAt");
diff --git a/prisma/schema.prisma b/prisma/schema.prisma
index 0d57b4e..1764939 100644
--- a/prisma/schema.prisma
+++ b/prisma/schema.prisma
@@ -399,6 +399,7 @@ model VideoAsset {
   uploadedByGuestName      String?
   billedUserId             String
   billedUser               User               @relation("VideoAssetBilledTo", fields: [billedUserId], references: [id], onDelete: Cascade)
+  sizeBytes                BigInt             @default(0) @map("size_bytes")
   createdAt                DateTime           @default(now())
   updatedAt                DateTime           @updatedAt
 
@@ -687,6 +688,19 @@ model WatchProgress {
   @@map("watch_progress")
 }
 
+// Tracks in-flight R2 upload slots so concurrent uploads are counted against quota
+// before the VideoAsset record is committed. Rows expire after a short TTL.
+model UploadReservation {
+  id           String   @id @default(cuid())
+  billedUserId String
+  sizeBytes    BigInt
+  expiresAt    DateTime
+  createdAt    DateTime @default(now())
+
+  @@index([billedUserId, expiresAt])
+  @@map("upload_reservations")
+}
+
 // Rate limiting table (created as UNLOGGED via raw SQL migration)
 // Defined here so `prisma db push` doesn't drop it
 model RateLimit {
diff --git a/scripts/backfill-asset-sizes.ts b/scripts/backfill-asset-sizes.ts
new file mode 100644
index 0000000..1c901a5
--- /dev/null
+++ b/scripts/backfill-asset-sizes.ts
@@ -0,0 +1,93 @@
+/**
+ * One-off backfill: populate size_bytes on existing VideoAsset rows (R2_IMAGE, R2_AUDIO)
+ * that still have the default value of 0.
+ *
+ * Run with:
+ *   bun scripts/backfill-asset-sizes.ts
+ *
+ * Dry-run (no writes):
+ *   bun scripts/backfill-asset-sizes.ts --dry-run
+ */
+import 'dotenv/config';
+import { HeadObjectCommand } from '@aws-sdk/client-s3';
+import { db, disconnectDb } from '../lib/db';
+import { r2Client, R2_BUCKET_NAME } from '../lib/r2';
+import { runWithConcurrency } from '../lib/async-pool';
+
+const DRY_RUN = process.argv.includes('--dry-run');
+const CONCURRENCY = 20;
+
+function sourceUrlToR2Key(sourceUrl: string): string | null {
+  if (sourceUrl.startsWith('/api/upload/image/')) {
+    const filename = sourceUrl.slice('/api/upload/image/'.length);
+    return filename ? `images/${filename}` : null;
+  }
+  if (sourceUrl.startsWith('/api/upload/audio/')) {
+    const filename = sourceUrl.slice('/api/upload/audio/'.length);
+    return filename ? `voice/${filename}` : null;
+  }
+  return null;
+}
+
+async function getR2ObjectSize(key: string): Promise<number | null> {
+  try {
+    const head = await r2Client.send(new HeadObjectCommand({ Bucket: R2_BUCKET_NAME, Key: key }));
+    return head.ContentLength ?? null;
+  } catch {
+    return null;
+  }
+}
+
+async function main() {
+  console.log(`Starting backfill${DRY_RUN ? ' (DRY RUN)' : ''}…`);
+
+  const assets = await db.$queryRaw<{ id: string; sourceUrl: string; provider: string }[]>`
+    SELECT id, "sourceUrl", provider
+    FROM video_assets
+    WHERE provider IN ('R2_IMAGE', 'R2_AUDIO')
+      AND size_bytes = 0
+  `;
+
+  console.log(`Found ${assets.length} assets with sizeBytes = 0`);
+  if (assets.length === 0) {
+    await disconnectDb();
+    return;
+  }
+
+  let updated = 0;
+  let skipped = 0;
+  let missing = 0;
+
+  await runWithConcurrency(assets, CONCURRENCY, async (asset) => {
+    const key = sourceUrlToR2Key(asset.sourceUrl);
+    if (!key) {
+      console.warn(`  [SKIP] ${asset.id} — cannot derive R2 key from: ${asset.sourceUrl}`);
+      skipped++;
+      return;
+    }
+
+    const size = await getR2ObjectSize(key);
+    if (size === null) {
+      console.warn(`  [MISS] ${asset.id} — object not found in R2: ${key}`);
+      missing++;
+      return;
+    }
+
+    if (!DRY_RUN) {
+      await db.$executeRaw`
+        UPDATE video_assets SET size_bytes = ${BigInt(size)} WHERE id = ${asset.id}
+      `;
+    }
+
+    console.log(`  [OK]   ${asset.id} — ${key}: ${size} bytes`);
+    updated++;
+  });
+
+  console.log(`\nDone. Updated: ${updated}, Skipped: ${skipped}, Missing in R2: ${missing}`);
+  await disconnectDb();
+}
+
+main().catch((err) => {
+  console.error(err);
+  process.exit(1);
+});