Summary

MS Teams file upload currently relies on simple PUT upload and has a documented gap for files larger than 4MB.

Why this matters

• Real-world assistant workflows frequently produce files >4MB (screenshots, PDFs, logs, exports).
• Current behavior likely fails for a common size band and degrades delivery reliability in Teams channels/chats.

Evidence

extensions/msteams/src/graph-upload.ts includes:

• comment: simple upload up to 4MB
• TODO: For files >4MB, implement resumable upload session.

Expected behavior

Uploads above 4MB should automatically switch to Graph upload session flow, chunking and committing successfully.

Suggested fix

• Add createUploadSession path for >4MB buffers.
• Implement chunked upload with retry/backoff for transient 429/5xx.
• Keep existing small-file fast path for <=4MB.
• Add tests for boundary cases (just below/above 4MB, retry, final commit failure).

Scope

extensions/msteams/src/graph-upload.ts