[Bug] `purge_deregistered_hotkeys` leaves orphaned `pending_confirms` rows

[kiannidev]

Summary

When a miner deregisters, purge_deregistered_hotkeys calls state_store.delete_hotkey, which clears rate_events, swap_outcomes, and reservation_pins but not pending_confirms. Queued user confirms for that hotkey keep draining and voting until reservation expiry or contract rejection.

Impact

• Wasted work signing vote_initiate for a miner no longer in the metagraph.
• Stale queue rows survive indefinitely (until purge_expired_pending_confirms) even though scoring/state for that hotkey was dropped.
• Operators see PendingConfirm [… UID ? (hotkey…)] after deregistration with no clear cleanup.

Current behavior

delete_hotkey omits the pending table:

    def delete_hotkey(self, hotkey: str) -> None:
        with self.lock:
            conn = self.require_connection()
            conn.execute('DELETE FROM rate_events WHERE hotkey = ?', (hotkey,))
            conn.execute('DELETE FROM swap_outcomes WHERE miner_hotkey = ?', (hotkey,))
            conn.execute('DELETE FROM reservation_pins WHERE miner_hotkey = ?', (hotkey,))
            conn.commit()

purge_deregistered_hotkeys only triggers that helper:

def purge_deregistered_hotkeys(self: Validator) -> None:
    current_hotkeys = set(self.metagraph.hotkeys)
    stale = {hk for (hk, _, _) in self.last_known_rates.keys()} - current_hotkeys
    if not stale:
        return
    for hk in stale:
        self.state_store.delete_hotkey(hk)

initialize_pending_user_reservations still iterates all queued rows with no metagraph membership check.

Expected behavior

delete_hotkey (or purge_deregistered_hotkeys) also deletes pending_confirms for the hotkey. Log when a deregistered miner had queued confirms removed.

How to reproduce

1. User queues SwapConfirm for miner M (unconfirmed source tx).
2. Miner M deregisters from the subnet before the queue drains.
3. purge_deregistered_hotkeys runs — rates/pins cleared, pending_confirms row remains.
4. Forward steps keep processing PendingConfirm for UID ? until expiry.

Proposed fix

Add DELETE FROM pending_confirms WHERE miner_hotkey = ? to delete_hotkey. Extend test_state_store.py::test_delete_hotkey_* to assert pending row removal. Optionally skip vote_initiate in initialize_pending when hotkey ∉ metagraph as defense in depth.