`Path.exists()` returns False for ELOOP and ENOTDIR, so a symlink loop or a
file where the parent directory should be read as an empty store. The read
now catches FileNotFoundError only. An existing zero-byte file is refused
with ValueError, like any other undecodable store, matching the Rust and C#
runtimes. `[0x90]` stays an empty legacy store.
Refusal text no longer points at a variant-aware runtime: an unsupported
header names the format found, and a v1 record with a fifth slot says the
file is not a valid store.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
202c4bbd63