BUG: Multipart Payload (Image + Text) Dropping Attachments on New Session Creation (Claude Sonnet 4.6)

To the Pickaxe Engineering Team,

I am encountering a reproducible payload handoff issue with the Pickaxe vision integration. When a user starts a brand new chat session and sends an image AND text in their very first message, Pickaxe’s backend is dropping the image from the payload before it reaches the Anthropic API.

The AI receives the text prompt, but registers zero image attachments.

My Environment & Setup:

  • Model: claude-sonnet-4-6

  • Capabilities: “Allow users to upload files” is set to “This thread only”

  • Token Allocations: * Input Length: 45,000

    • Uploaded Documents: 45,000

    • User Memories: 10,000

    • Memory Buffer: 11,410

    • Output: 1,800

  • Total Context Load: ~119,589 tokens. This is only 12% of Claude’s 999,000 capacity. This definitively rules out token truncation or context window overflow as the cause.

Steps to Reproduce:

  1. Open a brand new chat session via a live share link (Incognito window).

  2. Click the paperclip and attach an image (e.g., a standard PNG screenshot).

  3. Type a text prompt in the exact same message box (e.g., “Give me a transcript of this conversation”).

  4. Hit Send.

Actual Behavior: Claude responds stating that it cannot see an image or that no image was provided (e.g., “No image or screenshot attached to your message”). The token metrics verify that the image file was not processed or sent to the model.

Expected Behavior: The AI should process the image via its native vision capabilities and execute the text prompt based on the visual context.

Diagnostic Proof (Why this is a Pickaxe payload assembly issue): I can completely bypass this bug using the exact same prompt and token settings if I separate the actions into two API calls.

  • If the user uploads the image by itself on turn 1, it doesn’t acknowledge anything was sent (see attached image)

  • It asks for image then if I upload image it reads it.

  • If the user uploads an image + text on turn 3 of an already active chat, it works flawlessly.

Hypothesis: There appears to be a race condition or payload assembly error occurring only on the creation of a new chat session. The Pickaxe system prioritizes sending the lightweight text prompt to establish the session with Anthropic, and fails to append the heavier image file to the context window before API handoff.

Could your engineering team look into how initial multipart (text + image) payloads are being routed to the Anthropic API on session start? Let me know if you need my specific Pickaxe workspace ID or share links to test.

Hi @femalenatured,

Thank you for such a detailed write-up, this is incredibly helpful.

I’ve logged this with our engineering team under PRD-789 so they can investigate the payload handling on session start. The screenshots and step-by-step reproduction you shared made it much easier to understand what’s going on.

I wasn’t able to consistently reproduce this on my end, but I did notice some inconsistent behavior as well, so I’m sharing this with the engineering team for a deeper look.

Really appreciate you taking the time to document this so clearly. I’ll keep you posted as soon as I have an update.

I just added more context in a different post here. I am running into this problem less ish. But i think it has something to do with using on mobile versus desktop. Desktop seems to be the issue more than mobile. When on mobile it usually works first try.

Hi @femalenatured, thanks for the patience.

quick update from engineering:

You were right about something being off in the first message flow. The issue was that requests to Anthropic were sometimes failing because of how the image URL was being sent. When that happened, the system would occasionally fall back to OpenAI, which made things feel inconsistent.

Fix is now in place. Anthropic is correctly receiving both image and text from the very first message.

Would you mind trying again and confirming on your end? Happy to jump in if anything still feels off :folded_hands: