Address Copilot review on #1403: the test seeked unconditionally to
offset 40960 with only `pre_size > 16384` as a guard. If pre_size sat
between 16384 and 40960 + 16384 = 57344 (e.g., on a chromadb version
that allocated fewer pages on init, or a future schema change), the
seek would extend the file with zero-padding and the original pages
would stay intact — quick_check would still pass on the (untouched)
real data, and the regression guard would silently skip detecting a
preflight-ordering regression.
Compute the offset from pre_size, page-aligned, with explicit asserts
that the file is large enough to mangle 4 pages without truncating
the header or extending past EOF.
Igor Lins e Silva
7b151039c9