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.agents/skills/cloudflare-deploy/references/r2/gotchas.md

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+# R2 Gotchas & Troubleshooting
+
+## List Truncation
+
+```typescript
+// ❌ WRONG: Don't compare object count when using include
+while (listed.objects.length < options.limit) { ... }
+
+// ✅ CORRECT: Always use truncated property
+while (listed.truncated) {
+  const next = await env.MY_BUCKET.list({ cursor: listed.cursor });
+  // ...
+}
+```
+
+**Reason:** `include` with metadata may return fewer objects per page to fit metadata.
+
+## ETag Format
+
+```typescript
+// ❌ WRONG: Using etag (unquoted) in headers
+headers.set('etag', object.etag); // Missing quotes
+
+// ✅ CORRECT: Use httpEtag (quoted)
+headers.set('etag', object.httpEtag);
+```
+
+## Checksum Limits
+
+Only ONE checksum algorithm allowed per PUT:
+
+```typescript
+// ❌ WRONG: Multiple checksums
+await env.MY_BUCKET.put(key, data, { md5: hash1, sha256: hash2 }); // Error
+
+// ✅ CORRECT: Pick one
+await env.MY_BUCKET.put(key, data, { sha256: hash });
+```
+
+## Multipart Requirements
+
+- All parts must be uniform size (except last part)
+- Part numbers start at 1 (not 0)
+- Uncompleted uploads auto-abort after 7 days
+- `resumeMultipartUpload` doesn't validate uploadId existence
+
+## Conditional Operations
+
+```typescript
+// Precondition failure returns object WITHOUT body
+const object = await env.MY_BUCKET.get(key, {
+  onlyIf: { etagMatches: '"wrong"' }
+});
+
+// Check for body, not just null
+if (!object) return new Response('Not found', { status: 404 });
+if (!object.body) return new Response(null, { status: 304 }); // Precondition failed
+```
+
+## Key Validation
+
+```typescript
+// ❌ DANGEROUS: Path traversal
+const key = url.pathname.slice(1); // Could be ../../../etc/passwd
+await env.MY_BUCKET.get(key);
+
+// ✅ SAFE: Validate keys
+if (!key || key.includes('..') || key.startsWith('/')) {
+  return new Response('Invalid key', { status: 400 });
+}
+```
+
+## Storage Class Pitfalls
+
+- InfrequentAccess: 30-day minimum billing (even if deleted early)
+- Can't transition IA → Standard via lifecycle (use S3 CopyObject)
+- Retrieval fees apply for IA reads
+
+## Stream Length Requirement
+
+```typescript
+// ❌ WRONG: Streaming unknown length fails silently
+const response = await fetch(url);
+await env.MY_BUCKET.put(key, response.body); // May fail without error
+
+// ✅ CORRECT: Buffer or use Content-Length
+const data = await response.arrayBuffer();
+await env.MY_BUCKET.put(key, data);
+
+// OR: Pass Content-Length if known
+const object = await env.MY_BUCKET.put(key, request.body, {
+  httpMetadata: {
+    contentLength: parseInt(request.headers.get('content-length') || '0')
+  }
+});
+```
+
+**Reason:** R2 requires known length for streams. Unknown length may cause silent truncation.
+
+## S3 SDK Region Configuration
+
+```typescript
+// ❌ WRONG: Missing region breaks ALL S3 SDK calls
+const s3 = new S3Client({
+  endpoint: `https://${accountId}.r2.cloudflarestorage.com`,
+  credentials: { ... }
+});
+
+// ✅ CORRECT: MUST set region='auto'
+const s3 = new S3Client({
+  region: 'auto', // REQUIRED
+  endpoint: `https://${accountId}.r2.cloudflarestorage.com`,
+  credentials: { ... }
+});
+```
+
+**Reason:** S3 SDK requires region. R2 uses 'auto' as placeholder.
+
+## Local Development Limits
+
+```typescript
+// ❌ Miniflare/wrangler dev: Limited R2 support
+// - No multipart uploads
+// - No presigned URLs (requires S3 SDK + network)
+// - Memory-backed storage (lost on restart)
+
+// ✅ Use remote bindings for full features
+wrangler dev --remote
+
+// OR: Conditional logic
+if (env.ENVIRONMENT === 'development') {
+  // Fallback for local dev
+} else {
+  // Full R2 features
+}
+```
+
+## Presigned URL Expiry
+
+```typescript
+// ❌ WRONG: URL expires but no client validation
+const url = await getSignedUrl(s3, command, { expiresIn: 60 });
+// 61 seconds later: 403 Forbidden
+
+// ✅ CORRECT: Return expiry to client
+return Response.json({
+  uploadUrl: url,
+  expiresAt: new Date(Date.now() + 60000).toISOString()
+});
+```
+
+## Limits
+
+| Limit | Value |
+|-------|-------|
+| Object size | 5 TB |
+| Multipart part count | 10,000 |
+| Multipart part min size | 5 MB (except last) |
+| Batch delete | 1,000 keys |
+| List limit | 1,000 per request |
+| Key size | 1024 bytes |
+| Custom metadata | 2 KB per object |
+| Presigned URL max expiry | 7 days |
+
+## Common Errors
+
+### "Stream upload failed" / Silent Truncation
+
+**Cause:** Stream length unknown or Content-Length missing  
+**Solution:** Buffer data or pass explicit Content-Length
+
+### "Invalid credentials" / S3 SDK
+
+**Cause:** Missing `region: 'auto'` in S3Client config  
+**Solution:** Always set `region: 'auto'` for R2
+
+### "Object not found"
+
+**Cause:** Object key doesn't exist or was deleted  
+**Solution:** Verify object key correct, check if object was deleted, ensure bucket correct
+
+### "List compatibility error"
+
+**Cause:** Missing or old compatibility_date, or flag not enabled  
+**Solution:** Set `compatibility_date >= 2022-08-04` or enable `r2_list_honor_include` flag
+
+### "Multipart upload failed"
+
+**Cause:** Part sizes not uniform or incorrect part number  
+**Solution:** Ensure uniform size except final part, verify part numbers start at 1