Warn when node is using unsafe cltv_expiry_delta value (<18)

[manreo]

Is your feature request related to a problem? Please describe.
See details here:
lightning/bolts#789
and here:
https://twitter.com/realtbast/status/1283298246983659520

I think it would be very efficient to the network if ThunderHub will show a warning when the node has channels with cltv_expiry_delta lower than the recommended value (there are more than 7k such channels on mainnet)

Describe the solution you'd like
I assume some warning that can be disabled in the settings.

[apotdevin]

In the details page if the channel has a lower than recommended CLTV it shows a small warning that you should increase it. Is this what you refer to?

[manreo]

Amazing! I did not know that.

Not sure how unsecured it is to use a low CLTV (@t-bast?) but maybe you should also add a global warning:

Thanks!

[apotdevin]

Will look into it, if it makes sense to have a global notification or maybe a bigger notification on the details page

PS: if you go to settings > privacy card > values > hide you can hide all number values on ThunderHub 😉🙈

[t-bast]

Using a low cltv_expiry_delta is really asking for trouble (it means you're confident that in case of close, you're able to get many transactions confirmed very quickly - and when on-chain fees spike, you're screwed).

Nodes won't be penalized much in path-finding for using a high enough cltv_expiry_delta, so they should strongly consider it!

[apotdevin]

@t-bast thub will show an error if the CLTV is below 14 and a warning if it's below 24, what do you think about these defaults?

[t-bast]

@apotdevin great, thanks! Could you bump those values to error below 18 and warning below 34, to match the values in the spec?

Ideally users will read some node operator guide at some point as well (at least if they plan on putting non-negligible amounts) and those guides should explain the trade-offs in details.

[apotdevin]

For sure, changed in c05f02a

Thanks!