attachments: large PDF returns HTTP 500 during Prompt.Base64 validation #57116

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1. opencode-agent commented on Oct 19, 2026

   

   opencode-agentBot

   on Oct 19, 2026 – with OpenCode Agent

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   Thanks for the thorough report and the direct API reproduction. I think this is a duplicate of #45558.

   The 500 doesn't come from your PDF or from a size limit. The Prompt.Base64 check in packages/schema/src/prompt.ts uses the repeated-group regex you quoted. In the Bun runtime that ships with OpenCode, it silently returns false for valid base64 once the string is longer than a few MB. That shows up as InvalidValue rather than the stack overflow you saw in Node. Your 1 MiB and 4 MiB prefixes pass and the full 10 MB file fails, which fits that. The regex hasn't changed on dev yet, and a fix is proposed in PR #51272, which hasn't been merged.

   Possible duplicates and related issues, ordered by likelihood:

   • attachments: dragging file or pasting file path into input fails session setup (Prompt.Base64 500 on /prompt) #45558: same Prompt.Base64 500 on POST /api/session/<id>/prompt from normalizeImageAttachment, with the root-cause analysis and reports on many 2.0.x versions
   • attachments: large files (~6MB+) crash the prompt with HTTP 500 instead of a size-limit error #54323: a 6.6 MB PDF failing with the same 500 (closed as a duplicate of attachments: dragging file or pasting file path into input fails session setup (Prompt.Base64 500 on /prompt) #45558)
   • session: multi-MB inline attachment makes a session permanently fail to decode #55110: the same regex making a session fail to load after a large attachment was saved (closed as a duplicate of attachments: dragging file or pasting file path into input fails session setup (Prompt.Base64 500 on /prompt) #45558)
   • fix(schema): validate canonical base64 without a backtracking regex #51272: the open PR that replaces the regex with a check that works on large strings

   Until it's fixed, the workaround you found still works: let the agent read the PDF from its local path instead of attaching it.

   The bot will close this issue as a duplicate in 1 day unless you reply explaining how your problem is different. Please subscribe to #45558 to follow progress.
2. opencode-agent

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   on Oct 19, 2026
3. opencode-agent

   closed this as duplicateon Oct 20, 2026
4. opencode-agent commented on Oct 20, 2026

   

   opencode-agentBot

   on Oct 20, 2026 – with OpenCode Agent

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   Closing this as a duplicate of #45558, since there was no reply saying how it's different. It's the same Prompt.Base64 validation failure that gives HTTP 500 on attachments over about 5–6 MB, including your 9.67 MiB PDF on 2.0.32. Closing just keeps the discussion in one place; the bug itself is still open. The proposed fix, PR #51272, hasn't been merged yet, so please subscribe to #45558 or #51272 to follow it. Until then, letting the agent read the PDF from its local path still works. If your problem turns out to be different, feel free to reply here.