Heid bug hunt, hulda, second round on 92c774e:
- A lone surrogate was dropped at the final decode, after the leading-dot
rule had already run, so "\ud800.forever" came out as .forever, the
keep marker, and "\ud800.." as "..". The NUL and every unencodable
character now go first, in one pass, so nothing dropped later can shield
a dot. Starlette decodes a multipart filename strictly (utf-8, else
latin-1), so this was not reachable over HTTP; the helper is now right by
construction regardless.
- A suffix too long to keep was cut like text, and the cut could land on a
shorter suffix that means something: "….png" out of "….pngxxxx…"
became an image. A cut that changes classify/doc_kind now has its dots
neutralised.
- The 16-byte extension threshold was unguarded (every test suffix was 4
bytes); a .jpeg case pins it.
Falsifiers: tests/mutations/upload_names.toml, 7/7 proved. Not taken here,
as they sit in the upload route rather than this helper: the pickup-id
mkdir outside the try (a FileExistsError race), rmtree(ignore_errors)
hiding a failed cleanup, and a CancelledError skipping cleanup.
vh
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