irisandClaude Opus 5
6f149398d0
A resume splices: it appends bytes from wherever the server is now onto whatever is already on disk. If the file changed upstream in between, the result is exactly the failure that survives every cheap check -- the right number of bytes, the wrong contents, and no error anywhere. HuggingFace files do get updated, so this is a real path rather than a theoretical one. `If-Range` is the header for this and would have been the tidy answer, but HuggingFace's CDN ignores it: probed today, a deliberately stale validator still answers 206 with the ranged bytes rather than 200 with the whole body. So the check is done here instead. A partial now has an identity file beside it holding the ETag it was written against, written before the body so an interrupted download still knows what it is a piece of. On resume, the response's ETag is compared against it, and a mismatch throws the partial away and asks again from zero. A partial with no identity at all is not resumed either -- it could be a fragment of anything. The sha256 HuggingFace publishes is now also checked before the file gets its real name, so a bad one is never offered to be run. That is belt-and-braces after the above rather than the primary defence, which is the right order: detecting corruption after downloading gigabytes is worth far less than not creating it. Verified by planting one: a 60 MB partial of random bytes with an identity file naming a revision that does not exist. The server logged "changed upstream since the partial was written -- starting again", restarted from zero rather than appending, and the finished file's sha256 matches the published one. Repeated the honest resume too -- cancel at 145 MB, restart, resume at 162 MB, correct hash. Thanks to dev-updater's session for the If-Range idea and for saying to confirm the CDN honours it rather than assume, which is exactly what it turned out not to do. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_017xn8nHw1tw1R6PtiY1eEtw