prisma-risk / tsoracle / 26379815675

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fix(codec): reject trailing bytes after a valid postcard body (#379)

decode used postcard::from_bytes, which stops once the target type is
fully read and silently ignores any bytes beyond it. For a version-
prefixed on-disk codec whose whole purpose is catching format drift,
that swallows a corruption signal: a partial overwrite that leaves
stale tail bytes behind decodes as a clean record.

Switch decode to postcard::take_from_bytes and reject a non-empty
remainder with a new CodecError::TrailingBytes { extra } variant. The
existing decode_rejects_truncated_input test covered too-few bytes; add
decode_rejects_trailing_bytes for the too-many case.

All three downstream codec_io_error matchers use a catch-all arm, so the
new variant maps to a generic IO error without code changes.

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