Summary

Attaching a PDF file to a prompt in the TUI crashes prompt submission with an HTTP 500: the server fails schema validation inside SessionPrompt.normalizeImageAttachment (the attachment's base64 string does not match the Prompt.Base64 pattern), the client surfaces Failed to set up session: UnexpectedStatus: 500, and the message is not persisted — the targeted session is left completely empty.

Impact: any attempt to attach a PDF on this setup repeatedly returns 500; the user cannot attach PDFs at all, with no clear error explaining why.

Environment

• opencode version: v2.1.2 (official install)
• OS: Darwin 27.0.0, arm64 (macOS, Apple Silicon M1)
• Terminal: Apple Terminal, TERM=xterm-256color, COLORTERM=truecolor
• Shell: /bin/zsh
• Install/channel: latest
• Active plugins: none (no plugin key in ~/.config/opencode/opencode.json, nothing under .opencode/)

Reproduction

1. Run opencode (v2.1.2) in Apple Terminal.
2. Start a new session.
3. Attach a PDF file to the prompt (added via file selection in the TUI).
4. Send the prompt.

Result: the client shows "Failed to set up session — UnexpectedStatus: 500". The sessions targeted by the failing POST remain empty (GET /api/session/{id}/message returns {"data":[],"cursor":{...}}).

Expected Behavior

Either (a) submit the prompt and handle the non-image attachment gracefully, or (b) reject the unsupported attachment type with a clear, actionable validation error — not an unhandled HTTP 500 and a cryptic "Failed to set up session" message.

Actual Behavior

Server log (~/.local/share/opencode/log/opencode.log) shows two failing POSTs, both returning http.status=500:

level=INFO http.method=POST http.url=/api/session/ses_...1/prompt http.status=500
cause="Error: Schema validation failed
  at jd (/$bunfs/root/chunk-ebxzfa7x.js:2:28720)
  at <anonymous> (/$bunfs/root/chunk-zpbe9kf3.js:124:299)
  at SessionPrompt.normalizeImageAttachment (/$bunfs/root/chunk-zpbe9kf3.js:124:23)
  at SessionPrompt.materializeAttachment (/$bunfs/root/chunk-mdmwmx3f.js:18:25988)
  at SessionPrompt.prepare (/$bunfs/root/chunk-zpbe9kf3.js:140:5532)
  at Session.prompt (/$bunfs/root/chunk-bqqk6a8d.js:440:7488) {
  [cause]: Error: { ... "_tag":"Filter", "annotations":{"expected":"a string matching the RegExp ^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=)?$" ... "identifier":"Prompt.Base64" ... }, "issues":[{ ... "_tag":"InvalidValue"}] }
}"

The normalized "base64" content is apparently the raw PDF (or a non-base64-encoded representation), failing the Prompt.Base64 regex and throwing unhandled.

Session IDs redacted.

Additional Context

• The background service itself was healthy at the time (opencode service status OK, opencode api get /api/info → version 2.1.2, PID alive), so this is not a service-down problem.
• Related observation from the same period, filed here as context in case it helps: a session that contains a message with an unsupported attachment (audio/file content type, error snipped below) fails every subsequent message with Failed to drain Session: Upstream request failed: [unsupported_content_type] Messages may contain text, images and video; this model does not read audio or files. — i.e., the bad message persists in history and permanently poisons the session; there is no toast or recovery path to drop the offending message.
• Frequency: reproduced on 2 consecutive attempts, once in each of 2 different new sessions.
• Workaround: paste the content as text or attach a PNG/JPG screenshot instead of the PDF; do not re-use the poisoned session.