a negative `MaxDepth` really was unbounded, and nothing noticed an archive nested inside a copy of itself. A zip quine at `-1` recursed until memory, disk or file descriptors ran out, running the full sub-pipeline at every level.
- the walk keeps a stack of the digests of the archives it's inside, and an archive identical to one of them is recorded as an unknown instead of being entered
- negative depth now stops at 16 levels (docs and CLI description updated)
- cancellation is checked between candidates, so a cancelled scan stops walking instead of finishing the archive tree
the three unknown-recording blocks in `processArchive` became a one-line helper to stay under `funlen`.
Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>
Alex Goodman
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