fix: harden upload resilience and contracts

app/api/upload/check/route.ts

@@ -4,8 +4,7 @@ import { getRemoteFolder } from '@/lib/github'
 import { classifyFileChanges } from '@/lib/diff-files'
 import { getModelFolderPath } from '@/lib/model-paths'
 import { ensurePreparedStagingAssets } from '@/lib/upload-staging'
-import { parseStagingRequestBody } from '@/lib/upload-request'
-import { getErrorMessage } from '@/lib/guards'
+import { readStagingRequestBody, uploadErrorResponse } from '@/lib/upload-request'
 import type { FileDiff } from '@/lib/types'
 
 export const runtime = 'nodejs'
@@ -22,15 +21,13 @@ export async function POST(req: NextRequest) {
   let stagingId: string
 
   try {
-    const body: unknown = await req.json()
-    stagingId = parseStagingRequestBody(body).stagingId
+    stagingId = (await readStagingRequestBody(req)).stagingId
   } catch (err) {
-    const message = getErrorMessage(err)
-    return NextResponse.json({ success: false, error: message }, { status: 400 })
+    return uploadErrorResponse(err, 400)
   }
 
   try {
-    const { folderName, filesToPush } = await ensurePreparedStagingAssets(stagingId)
+    const { folderName, filesToPush, deliveryMode, compressionError } = await ensurePreparedStagingAssets(stagingId)
     const folderPath = getModelFolderPath(folderName)
     const { exists, files } = await getRemoteFolder(folderPath)
 
@@ -53,12 +50,18 @@ export async function POST(req: NextRequest) {
         exists: true,
         path: folderPath,
         diffs,
+        deliveryMode,
+        compressionError,
       })
     }
 
-    return NextResponse.json({ success: true, exists: false })
+    return NextResponse.json({
+      success: true,
+      exists: false,
+      deliveryMode,
+      compressionError,
+    })
   } catch (err) {
-    const message = getErrorMessage(err)
-    return NextResponse.json({ success: false, error: message }, { status: 500 })
+    return uploadErrorResponse(err, 500)
   }
 }