bug: transcript downloads get a .json filename when the stored media type differs in case #4982

Provide environment information

Not environment-specific: found in the webapp source at main @ c2b7a72 and reproduced with the webapp's own Vitest suite (macOS arm64, pnpm).

Describe the bug

downloadTranscript (apps/webapp/app/services/realtime/transcriptDownload.server.ts:11-15) picks the .jsonl filename only when the stored media type exactly equals TRANSCRIPT_BLOB_CONTENT_TYPE (application/vnd.trigger.transcript+ndjson):

contentType.split(";")[0]?.trim() === TRANSCRIPT_BLOB_CONTENT_TYPE

Media types are case-insensitive (RFC 9110 §8.3.1). An object whose Content-Type comes back in a different case, for example from an S3-compatible store or proxy that normalizes header values, is the same indexed transcript, but it downloads as snapshot.json rather than snapshot.jsonl. Line-oriented tools then get the wrong extension.

Expected: the comparison is case-insensitive, and the filename is .jsonl for any casing of the transcript media type.

Reproduction repo

N/A (unit test against this repo, below)

To reproduce

Add this to apps/webapp/app/services/realtime/transcriptDownload.server.test.ts:

test("uses a .jsonl filename for transcript media types regardless of case", () => {
  const object = new Response('{"version":2}\n', {
    headers: { "Content-Type": TRANSCRIPT_BLOB_CONTENT_TYPE.toUpperCase() },
  });
  const response = downloadTranscript(object, "packets/download/snapshot.json");
  expect(response.headers.get("Content-Disposition")).toBe('attachment; filename="snapshot.jsonl"');
});

On main it fails with filename="snapshot.json".

Additional information

A 1-line fix (lowercase before comparing) with this regression test and a .server-changes note is ready on the breken-ai/trigger.dev fork (breken/fix-transcript-mime-case). The related Vitest suite, oxfmt, oxlint and webapp typecheck pass. I'll open it as a draft PR with fixes #<this> once the account is vouched.

Prepared with AI assistance (Claude) from the breken-ai account.