v1 instrumentation (S1.20) eliminated 3 of 6 hypotheses: apply_fill_to_pos
arithmetic is fully clean (avg_px=0 realised=0 realized_pnl=0). But
pnl_track open branch still saw vwap_entry=0 (194 times) or > 21M (216
times) at the open transition.
v2 adds per-vwap-write-site counters so we can pinpoint which apply_fill
branch produced the bad vwap, plus captures the actual last-bad-vwap
value and the path id (1..6 = open-flat, scale-in zero/huge, flip-beyond
zero/huge, session-gap-saw-stale).
The 7th counter (vwap_session_gap_was_bad) fires when the session-gap
force-close path sees pos.vwap_entry already in a corrupt state pre-gap.
Logged at end of smoke as `nan_counters_v2: zero_flat=N huge_flat=N
zero_scale=N huge_scale=N zero_flip=N huge_flip=N session_gap_was_bad=N
| b0_last_bad_vwap=X b0_last_bad_path=N`.
19/19 stop_controller CUDA tests pass; 5/5 decision_floor_coldstart pass.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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