The complement to the per-function compare harness. Instead of "did this
function's declared outputs match", it asks "is the entire simulation state
still identical" -- so no region-declaration mistake can hide from it.
Coverage is PROVED, not declared: the digest tree is re-serialised and compared
byte-for-byte against the inflated save on every run. When that reconstruction
reproduces the stream, the whole file is a function of the digest's inputs. A
run that cannot account for the file says so and exits non-zero. This is the
direct answer to B4's three hooks that printed "0 diverged" over an empty
region set.
It localises. The root is the fold of a per-subsystem / per-object tree with
named objects, so the known load->re-save delta reports as exactly five leaves
-- /Summary/Checksum and four /Sim/players/Player[...]/Status 4->0 -- naming the
two Singularity players by id where the raw byte diff could only say "1st of
two". One real End Turn reports as 108 fully attributed differences.
Float-parity policy is explicit and strict by default (STATE_CHECKSUM.md 3):
raw IEEE-754 bits; a `canonical` policy for signed zero and NaN payloads only;
and deliberately NO tolerant hashing mode, because quantisation moves the cliff
rather than removing it and destroys the roll-up. Tolerance lives in the differ
as --ulps, applied after localisation. Corpus census: 0 NaN, 0 -0.0, 0
subnormals across 4,474 float leaves, so the strict default costs nothing today
and a test fails the day that changes.
Validated on the real saves (verify/results/state-checksum/): 10 files, 4
distinct contents, all STABLE + COVERED; chain record/verify works on the real
turn1-3 saves. The VM-driven replay loop is designed (section 5) but UNRUN.
Section 3.5 names the one question the host side cannot settle -- whether the
turn pipeline depends on x87 intermediate precision -- and the experiment that
would: force fpu_cw to 0x027f / 0x127f / 0x137f across End Turn and checksum
the three autosaves.
Also recorded: Summary.Checksum is NOT a byte sum over the inflated stream nor
a sum over the int leaves (both ruled out), so nobody repeats those two.
38 tests; sots-engine untouched, clean_room_check.sh OK.
fdd0b72b7a