Add `_hasRecenterTick` boolean guard to decouple bootstrap detection from
VWAP volume tracking. Before this fix, the bootstrap condition relied solely
on `cumulativeVolume == 0`, which made `lastRecenterTick==0` ambiguous:
it could mean "never recentered" or "previous recenter landed at tick 0
(price = 1.0 token ratio)".
The new guard ensures the direction comparison in the else-branch only
runs after a recenter has explicitly set `lastRecenterTick`, eliminating
the tick-0 ambiguity. Belt-and-suspenders: both `!_hasRecenterTick` and
`cumulativeVolume == 0` trigger bootstrap.
Tests added:
- test_hasRecenterTickGuardPreventsTick0Ambiguity
- test_vwapFrozenDuringBuyOnlyAfterSellRecenter
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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