Rung 1 of the identity ladder. A protective MBR (a type-0xEE entry) routes
probing to the GPT, authoritatively: gptFirstVolume verifies the LBA-1 header's
'EFI PART' signature and a header CRC-32 (inline reflected poly 0xEDB88320,
shared with the fixtures so parser and tests never drift onto a magic constant),
then walks the entry array — bounded by the declared gpt_entry_scan_maximum —
for the first entry with a non-zero type GUID and an overflow-safe in-device
range. That range check is the confinement-safety guard the driver's clamp
rests on, the invariant firstVolume already enforces for MBR, extended to
untrusted GPT metadata. The unique partition GUID becomes the identity key (the
id / mount-path handle); the 36-char partition name becomes the display label.
Three host tests (GUID-as-id; entry-past-device skipped and an all-out-of-range
table is null; a broken header/CRC is not a volume) — all three FAIL with the
GPT branch neutralized (3/7) and pass with it (7/7). Entry-array CRC deferred
(correctness-only; the range check carries the safety property).
Daniel Samson
020e31bc8f