[bug]: Neutrino pruning of channels not working properly

[ziggie1984]

Background

It seems like we are progressing our view on the chain although we are not really able to fetch the block in time. The node runner tried to close its channel which confirmed successfully onchain, however LND did not prune the graph correctly. This error was observed when finally updating the channel policies where the following error occured because the problem is, the channel is still in the graph_db, but not in the openChanBucket which causes this error when updating:

{
    "failed_updates": [
        {
            "outpoint": "xxx:0",
            "reason": "UPDATE_FAILURE_INVALID_PARAMETER",
            "update_error": "channel not found"
        }
    ]
}

And we still see the channel in the graphdb:

$ lncli getchaninfo ??
{
    "channel_id":  "??",
    "chan_point":  "??:0",
    "last_update":  1740174524,
    "node1_pub":  "??",
    "node2_pub":  "??",
    "capacity":  "???",
    "node1_policy":  {
        "time_lock_delta":  144,
        "min_htlc":  "1000",
        "fee_base_msat":  "1000",
        "fee_rate_milli_msat":  "1000",
        "disabled":  true,
        "max_htlc_msat":  "???",
        "last_update":  1740174524,
        "custom_records":  {},
        "inbound_fee_base_msat":  0,
        "inbound_fee_rate_milli_msat":  0
    },
    "node2_policy":  {
        "time_lock_delta":  80,
        "min_htlc":  "1000",
        "fee_base_msat":  "1000",
        "fee_rate_milli_msat":  "1",
        "disabled":  true,
        "max_htlc_msat":  "???",
        "last_update":  1740174491,
        "custom_records":  {},
        "inbound_fee_base_msat":  0,
        "inbound_fee_rate_milli_msat":  0
    },
    "custom_records":  {}
}

and the logs showed that the relevant block that closed the channel could not be fetched in time:

BTCN: Unable to process block connected (height=???, hash=???): did not get response before timeout

This should be fixed with the neutrino fetching refactor

Your environment

• version of lnd: 18.5
• version of btcd, bitcoind, or other backend: neutrino