[feature]: LND fails to sync channel graph with bitcoind blocksonly=1

[racarr202]

Is your feature request related to a problem? Please describe.
See issue #10111 for detailed background.

In short, following a node backend migration from neutrino to bitcoind, the node failed to sync the channel graph when the bitcoind instance was configured with blocksonly=1. The node hung silently, with no clear indication in the LND logs about the root cause.

Describe the solution you'd like
Either:

1. LND detects that bitcoind is running with blocksonly=1 and issues an error message stating that the blocksonly=1 setting is incompatible with LND. Perhaps a comment indicating this setting incompatibility could also be added to the lnd builders guide.
2. Resolve the underlying incompatibility issue if possible.

Describe alternatives you've considered
The only alternative I am aware of is for users to manually debug the issue.
A temporary workaround as proposed by @guggero was to set routing.assumechanvalid=true, but this bypasses the issue rather than solving the underlying problem.

Additional context

• The issue was observed on lnd 0.19.1-beta with bitcoind v28.1.knots20250305.
• A goroutine profile confirmed LND was stuck waiting on a block from bitcoind.

[Roasbeef]

If you run lnd in blocks only mode, then you can't get fee estimation. If you can't get fee estimation, your funds are at risk as we don't know how high a fee we need to pay to defend our funds in the case of a breach.

[saubyk]

Moving this issue to discussions, will reopen when development is planned