fix(proof): cross-platform tolerance gate for verify.py determinism

Definitive root cause of the failing determinism gate: the SHA-256 of
fixed-decimal-rounded features is bit-exact only WITHIN one CPU
microarchitecture. Windows and a second Linux box (ruvultra, identical
numpy 2.4.2/scipy 1.17.1) produce the same hash at every precision
(ca58956c), but the GitHub Azure runner diverges at EVERY precision
including 2 decimals (667eb054) — because pocketfft/BLAS reorders FP
reductions per-microarch and the ~1e-6 *relative* drift lands on
large-magnitude PSD bins as an absolute difference no fixed-decimal grid
can absorb. So no quantization can fix it; the primitive was wrong.

Fix: keep the bit-exact SHA-256 as the strong same-platform proof, and
add a relative-tolerance fallback (np.allclose, rtol=1e-4/atol=1e-6)
against a committed reference feature vector (expected_features_reference.npz,
36,800 float64 values). A run PASSES on either; tolerances sit ~100x over
the observed microarch drift and ~10x under any signal-meaningful change,
so real regressions still fail. Verified locally: bit-exact MATCH -> PASS,
and a corrupted hash falls through to TOLERANCE MATCH -> PASS. CI (Azure,
different hash) now passes via the tolerance path. Removes the temporary
sweep diagnostic.

Co-Authored-By: claude-flow <ruv@ruv.net>

.github/workflows/verify-pipeline.yml

@@ -58,20 +58,6 @@ jobs:
           print('Reference signal metadata validated.')
           "
 
-      - name: Quantization sweep (diagnostic — cross-microarch precision)
-        working-directory: archive/v1
-        env:
-          OMP_NUM_THREADS: "1"
-          OPENBLAS_NUM_THREADS: "1"
-          MKL_NUM_THREADS: "1"
-          VECLIB_MAXIMUM_THREADS: "1"
-          NUMEXPR_NUM_THREADS: "1"
-        run: |
-          for d in 6 5 4 3 2; do
-            h=$(PROOF_HASH_DECIMALS=$d python data/proof/verify.py --generate-hash 2>/dev/null | grep -i 'Computed:' | sed 's/.*Computed:[[:space:]]*//')
-            echo "SWEEP d=$d $h"
-          done
-
       - name: Run pipeline verification
         working-directory: archive/v1
         env: