Api V2 Gex Pin-Stability Get

What the Pin Strike has done during the session.

The third question in the reading order — regime, then confidence, then stability — and the only one the API could not previously answer. A pin that has held one strike since the open and a pin that has migrated thirty points are different signals wearing the same label; without this a drifting pin reads as a level that failed rather than one tracking a repricing book.

current_* is the pin standing right now, held_* the most recent value that has SETTLED, and current_established says whether they are the same. Migration is measured between settled levels only, so a one-sample tick at the bell is not reported as a move; net_migration is signed (negative = the pin has walked down). Sample counts, not minutes: the analytics cycle is ~60s but is not guaranteed to be, so the honest unit is "stored frames". Null-bodied (stability omitted) when the session carried no active pin at all — hide, don't zero.

The v2 freshness envelope. Present on every /api/v2/* response.