tmpnam() on the Windows CRT returns a bare, CWD-relative name (e.g. \sb4c.2), and io.open on it fails with Permission denied when the game's working directory is not writable -- a Program Files (or otherwise protected) install. postLog then dies before curl runs: the mod reports a send failure and no bytes leave the machine (confirmed on a Windows install: "could not create request body: \sb4c.2: Permission denied").
Stage the request body under the OS temp contract instead: TEMP/TMP on Windows (always set, always per-user writable), TMPDIR with a /tmp fallback on POSIX. The transport stays on plain io/os -- no love.filesystem dependency.
Tests updated to mock os.getenv and assert the staged path sits under the temp dir; 10/10 checks pass.
Shane McGovern