Function hold_invoice_claim_deadline 

fn hold_invoice_claim_deadline(htlcs: &[InvoiceHtlc]) -> u32

Block height at which LND is assumed to cancel an accepted HOLD invoice by itself, LND_ASSUMED_HOLD_EXPIRY_DELTA blocks before its earliest accepted HTLC expires, after which the gateway can no longer settle it. Without an accepted HTLC there is no deadline to trust, so it is 0.

The same holds once a keysend HTLC is accepted (see has_accepted_keysend_htlc): the invoice then keeps accepting further keysend HTLCs, and until it restarts LND neither reports them nor moves its cancel height for them.