feat(uploads): size one upload against the account's own quota

The per-file ceiling was a flat 5 GiB from the environment, which is both
too small for a paying account with 200 GB of storage and unaware of what
an upload actually costs. The provider derives its own renditions from the
file (1080p, 720p and down) and bills them to the same account, so a file
allowed to fill the quota exactly is over it by the time it finishes
processing.

The ceiling is now 80% of whatever limit the account is held to: 160 GB on
the plan, 2.4 GB on a cardless trial, and it moves on its own when either
number changes. OPENFRAME_MAX_VIDEO_UPLOAD_BYTES keeps working as an
absolute cap for a host that wants one, where the lower of the two applies,
and an instance running without billing has no quota to divide and falls
back to the flat 5 GiB. The refusal now names the ceiling, which the old
one left the client to guess.

Finalize re-checks only the host cap. Re-deriving the account's ceiling
there would delete a finished upload over a plan that lapsed while the
bytes were in flight, and an upload larger than what was declared is
already caught by the declared-size check beside it.

lib/storage-quota.ts

@@ -1,10 +1,15 @@
 import type { NextResponse } from 'next/server';
 import { db } from '@/lib/db';
 import { apiErrors } from '@/lib/api-response';
-import { isStripeFeatureEnabled } from '@/lib/feature-flags';
+import {
+  DEFAULT_MAX_VIDEO_UPLOAD_BYTES,
+  getConfiguredMaxVideoUploadBytes,
+  isStripeFeatureEnabled,
+} from '@/lib/feature-flags';
 import { getUserBunnyStorageBytes } from '@/lib/admin-stats';
 import { isPaidTier } from '@/lib/billing';
 import { getStorageLimitBytes } from '@/lib/trial-limits';
+import { formatSizeLimit } from '@/lib/upload-size';
 
 // 200 GB expressed in bytes
 export const PLAN_STORAGE_LIMIT_BYTES = BigInt(200) * BigInt(1024) * BigInt(1024) * BigInt(1024);
@@ -46,12 +51,41 @@ export async function getStorageContextForUser(userId: string): Promise<StorageC
 }
 
 /**
- * Whole gigabytes where the number is whole, which every ceiling we ship is.
- * A host that sets an odd one gets a decimal rather than a rounded lie.
+ * The share of an account's storage ceiling one single upload may take.
+ *
+ * A video costs more than the file that was handed to us: the provider derives
+ * its own renditions from it (1080p, 720p and down) and those land in the same
+ * account's usage. A file allowed to fill the whole quota would therefore be
+ * over the quota by the time it finished processing, so a fifth of the ceiling
+ * is left free for what the upload turns into.
  */
-function formatStorageLimit(bytes: bigint): string {
-  const gigabytes = Number(bytes) / 1024 ** 3;
-  return `${Number.isInteger(gigabytes) ? gigabytes : gigabytes.toFixed(1)} GB`;
+export const MAX_UPLOAD_SHARE_PERCENT = BigInt(80);
+
+/** The largest single file that fits under `limitBytes` with room to transcode. */
+export function getMaxUploadBytesForLimit(limitBytes: bigint): bigint {
+  return (limitBytes * MAX_UPLOAD_SHARE_PERCENT) / BigInt(100);
+}
+
+/**
+ * The largest single file this account may upload.
+ *
+ * Derived from the account's own ceiling rather than fixed, so the answer moves
+ * with the plan: 200 GB of storage allows a 160 GB file, and a cardless trial's
+ * 3 GB allows 2.4 GB. A host that has pinned an absolute cap still wins where
+ * it is the lower of the two, and a host running without billing has no quota
+ * to divide, so it falls back to the flat default.
+ */
+export async function getMaxVideoUploadBytesForUser(userId: string): Promise<bigint> {
+  const hostCeiling = getConfiguredMaxVideoUploadBytes();
+
+  if (!isStripeFeatureEnabled()) {
+    return hostCeiling ?? DEFAULT_MAX_VIDEO_UPLOAD_BYTES;
+  }
+
+  const { limitBytes } = await getStorageContextForUser(userId);
+  const quotaCeiling = getMaxUploadBytesForLimit(limitBytes);
+
+  return hostCeiling !== null && hostCeiling < quotaCeiling ? hostCeiling : quotaCeiling;
 }
 
 /**
@@ -68,8 +102,8 @@ export function storageExceededResponse(context: StorageContext): NextResponse {
   }
 
   return apiErrors.trialStorageExceeded(
-    `Your free trial includes ${formatStorageLimit(context.limitBytes)} of storage. ` +
-      `Upgrade to get ${formatStorageLimit(PLAN_STORAGE_LIMIT_BYTES)}.`
+    `Your free trial includes ${formatSizeLimit(context.limitBytes)} of storage. ` +
+      `Upgrade to get ${formatSizeLimit(PLAN_STORAGE_LIMIT_BYTES)}.`
   ) as NextResponse;
 }