fix(session): read text attachments as text for non-text/plain MIME types#34786
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adityachaudhary99 wants to merge 1 commit into
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fix(session): read text attachments as text for non-text/plain MIME types#34786adityachaudhary99 wants to merge 1 commit into
adityachaudhary99 wants to merge 1 commit into
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…ypes resolveUserPart only routed a file attachment through the readable-text (Read tool) path when its MIME was exactly "text/plain". An extension-less or unrecognized text file resolves to application/octet-stream, so it fell through to the branch that base64-encodes the raw bytes and prepends a synthetic Read tool-call frame — the model then received binary garbage (anomalyco#17301). This is the consumer side; the earlier anomalyco#26152 only fixed the `run --file` producer. Gate the text path on a shared isTextMime() check (text/*, json/xml/js, empty, and the octet-stream unknown fallback) so text files are read as UTF-8, sniffed images/PDFs still become proper attachments, and genuine binary fails closed. Closes anomalyco#17301 Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Issue for this PR
Closes #17301
Type of change
What does this PR do?
Attaching a text file could send binary-looking garbage to the model instead of the file's contents.
resolveUserPart(session/prompt.ts) only routed an attachment through the readable-text path (the Read tool) when its MIME was exactlytext/plain. A file with no extension — or any unrecognized text file — resolves toapplication/octet-stream, so it skipped that path and hit the branch that base64-encodes the raw bytes and prepends a syntheticCalled the Read tool…frame. The model then received a data-URL of raw bytes, which is the garbled output in the issue.The earlier #26152 fixed the
run --fileproducer (real MIME lookup), but the consumer here still only recognized literaltext/plain, so the interactive/upload path stayed broken (and extension-less files arguably got worse, since they now resolve to octet-stream).The fix gates the text path on a shared
isTextMime()check (text/*, JSON/XML/JS, empty, and theapplication/octet-streamunknown fallback) instead of an exact string. The Read tool already content-sniffs, so real text reads cleanly, sniffed images/PDFs still become proper attachments, and genuine binary now fails closed with an honest message instead of a garbled blob. Image/PDF MIMEs are untouched.How did you verify your code works?
Added two cases to
test/session/prompt.test.ts: a text file attached asapplication/octet-stream(the exact repro — an extension-less file) and astext/markdownboth produce a clean synthetic text part containing the file's text, with zero forwarded binary parts. I couldn't run the full suite in my isolated worktree (the@opencode-ai/coreworkspace alias resolves to a stale checkout there), so I rely on CI for the suite.Screenshots / recordings
N/A — not a UI change.
Checklist