[EgorGruzdev]

Problem

ticket_allocator_operators.bound_tickets / total_complexity are unsigned. When a counter has drifted below the real number of bound tickets (e.g. an external recount raced with Triage increments), OperatorProjector decrements it below zero and MySQL throws:

SQLSTATE[22003]: 1690 BIGINT UNSIGNED value is out of range in '(`bound_tickets` - 1)'

The exception aborts the projection: TicketProjector (weight 5) never runs after OperatorProjector (weight 0), so the ticket.closed event is stored but the ticket stays alive and bound to the operator, occupying a slot.

Change

• Operator::decrementToZero() — same flow as Model::decrement() (fires updating, so ReadonlyProjection protection is kept; touches updated_at; syncs attributes), but issues col = GREATEST(col, n) - n atomically in SQL. GREATEST(col - n, 0) would not help: col - n on unsigned zero fails before GREATEST is evaluated.
• OperatorProjector: all decrements in onTicketBound (previous operator), onTicketUnbound, onTicketClosed use it. Increments untouched.

Verified

In the host app against local MySQL, inside a rolled-back transaction: operator with bound_tickets = 0, close its ticket.

• before: QueryException 22003, ticket not deleted;
• after: counters 0, ticket soft-deleted.