Extends reset_session_state with 8 new regime_observer slot resets per
spec section "Regime observer reset policy at fold/eval boundaries":
- Transient state (FLAG/DURATION/TIMEOUT) → 0
- RECOVERY_FACTOR → 1.0
- TAIL_EVENT_RECENCY → 1e6 sentinel
- KELLY_EPS_RECOVERY_LIVE → 0.50 (= ε_max)
- PREV_WORST_PNL → 0 (CRITICAL — prevents spurious 3σ tail at boundary)
- POPART_MAX_ABS_REWARD_EMA → 0 (F4 envelope reset)
Welford state (M2/MEAN/COUNT) intentionally NOT reset — variance of
session_pnl_change is regime-invariant per pearl_adaptive_carryover_discipline.
Issue γ fix: without PREV_WORST_PNL reset, the first regime_observer call
after a fold boundary would see Δworst = 0 - (-\$15k_train) = +\$15k, fire
a spurious 3σ tail event, and peg ε_recovery at ε_min for 100 steps.
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