Resolver and built-in backend offset arithmetic currently contains unchecked or unwrap-based additions, and resolver code trusts backend byte counts. Define the intended error mapping, then replace overflow panics with typed fs errors and reject backends that report more bytes than the supplied buffer. Cover resolver, InMem, TarRo, and overlay copy paths. Deferred from #1318 to avoid changing established behavior during the refactor.
Resolver and built-in backend offset arithmetic currently contains unchecked or unwrap-based additions, and resolver code trusts backend byte counts. Define the intended error mapping, then replace overflow panics with typed fs errors and reject backends that report more bytes than the supplied buffer. Cover resolver, InMem, TarRo, and overlay copy paths. Deferred from #1318 to avoid changing established behavior during the refactor.