[Bug]: Pasting an unsupported document leaves the chat unrecoverable #12037

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1. juliusmarminge commented on Sep 16, 2026

   

   juliusmarminge

   on Sep 16, 2026

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   Confirmed in source. The quoted error is not a T3 string — it is Vercel AI SDK’s OpenAI-compatible converter ('file part media type ${mediaType}' functionality not supported). T3 reaches that path only through OpenCode.

   Composer correctly treats a pasted .html / text/html document as a generic file (the image denylist from #6574 / #7225 does not apply). ProviderService already puts a filesystem path in the prompt. OpenCode then also sends the file as a native part because isOpenCodeNativeFilePart allows every text/* type:

   • apps/server/src/provider/opencodeRuntime.ts (toOpenCodeFileParts)
   • apps/server/src/provider/Layers/OpenCodeAdapter.ts (session.promptAsync parts)

   That allowlist already excludes ZIP, BMP, SVG, and oversized PDFs so the model call does not fail before it starts. text/html was left on the native path. Many OpenCode model converters (especially OpenAI-compatible) reject it. Once the file part is stored in the OpenCode session, later prompts replay it and the same error returns — including on text-only follow-ups.

   Claude, Cursor, Grok, and Codex never send generic files as native parts. Antigravity embeds text/* as text. So this is OpenCode-specific.

   This is the same provider-history brick as #11295 (inline preview_snapshot PNGs), with a different trigger. Not a duplicate. #7225 / #6574 only gate unsupported images at attach time.

   What prior work did not fix

   Work	What it did	Why this still happens
   #6574 (merged; closed #7225 / #6020)	Reject HEIC/SVG/etc. in the composer	HTML is classified as file, not unsupported-image
   #8092 (file uploads)	Allow PDFs/ZIPs/other files	Intentional; OpenCode then over-promotes text/*
   #4200	Validate before turn.started so the UI does not wedge on working	Session can still persist the rejected file part
   #11295 (open)	Screenshot bytes in OpenCode history	Different payload; same inability to continue

   No open T3 PR closes this.

   Suggested fix

   In isOpenCodeNativeFilePart:

   1. Stop sending text/html (and likely other text/* types the converter rejects) as native file parts. Use the path line ProviderService already prepends. Folded clipboard pastes (source: pasted-text) already skip native parts.
   2. Safest allowlist: PNG/JPEG/GIF/WebP + application/pdf. That matches the comment in toOpenCodeFileParts and the ZIP/BMP/SVG tests.
   3. Do not add a global composer ban on HTML. Other providers already handle generic files without this converter.

   A MIME change does not rewrite file parts already in an OpenCode session.

   Workaround

   • New HTML/text documents on OpenCode: attach as usual only after a fix; until then, paste as text or point the agent at a file path.
   • Bricked chat: start a new thread. Rewind can work if it forks off the user message that carried the file part (OpenCodeAdapter.rollbackThread → session.fork). If the failed turn never created an assistant boundary, rewind to the last good turn or just start a new chat.

   Implementable from current main. Confirming the OpenCode model slug would be useful but is not required.

   Classification: bug · accepted · high (one paste can brick the OpenCode chat)
   Labels: add bug, accepted, via-triage
   Discord tags: providers, ui
2. juliusmarminge

   added

   bugSomething is broken or behaving incorrectly.Something is broken or behaving incorrectly.

   acceptedfeature request acceptedfeature request accepted

   via-triageFiled through npx t3 triageFiled through npx t3 triage

   on Sep 16, 2026
3. juliusmarminge

   closed this as completedin #2829on Oct 2, 2026