test: physical health and stricter parity in timing harness

Untimed physical-leaf/fluid health after warm-up and after each timed
window using the existing runner limits (finite macros, rho in [0.5,1.5],
max Mach <= 0.2); refined masks as in run_refined_dfg. Parity comparator
rejects unequal level counts and any infinity; matching NaN stays allowed
only as a storage mask. Regression tests for both. No numerical gate or
production change.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/validation/refined_dfg_timing.md

@@ -21,7 +21,10 @@ physics-gate or production change; no force or accuracy result is produced.
   every 100 steps in per-step loops).
 - Final populations and NaN masks must be bitwise identical to the first A repeat (A/B/C) or the
   first E repeat (E/E'); refined and uniform grids are never compared. Leaf/fluid populations
-  must be finite. All parity/health checks are untimed.
+  must be finite. Physical health (finite leaf/fluid macros, rho in [0.5, 1.5], max Mach <= 0.2,
+  the existing runner limits) is checked after warm-up and after each timed window. Matching NaN
+  is accepted only as a storage mask; any infinity or level-count mismatch fails parity. All
+  parity/health checks are untimed.
 - Cases run sequentially (uniform, then refined) in one process with startup serialized;
   variants are interleaved within each repeat. A-B and B-C are measured comparative
   differences under GPU variability, not exact causal decompositions.