doc: clarify that testnet min-difficulty is not optional #32095

1. 
   Sjors commented at 8:01 am on March 19, 2025: member

   When 20 minutes have gone by on testnet3 or testnet4, the next block MUST have difficulty 1. I’ve seen people be confused about this several times now in recent months. It doesn’t help that the code comment is wrong. So fixing that.

   The reason is that nBits must match exactly:

   https://github.com/bitcoin/bitcoin/blob/e568c1dd134e0318c46113cb7dfc23b40e2829e8/src/validation.cpp#L4212-L4215

2. doc: clarify that testnet min-difficulty is not optional 288481aabd
3. 
   DrahtBot commented at 8:01 am on March 19, 2025: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/32095.

   Reviews

   See the guideline for information on the review process.

   Type	Reviewers
   ACK	fjahr, kevkevinpal

   If your review is incorrectly listed, please react with 👎 to this comment and the bot will ignore it on the next update.

4. DrahtBot added the label Docs on Mar 19, 2025
5. 
   Sjors commented at 8:06 am on March 19, 2025: member

   Note that there’s a recent proposal to drop this rule entirely: https://gnusha.org/pi/bitcoindev/hU75DurC5XToqizyA-vOKmVtmzd3uZGDKOyXuE_ogE6eQ8tPCrvX__S08fG_nrW5CjH6IUx7EPrq8KwM5KFy9ltbFBJZQCHR2ThoimRbMqU=@protonmail.com/
6. 
   fjahr commented at 5:24 pm on March 19, 2025: contributor

   ACK 288481aabd77b90876489e39403b6eab9d4ae74d
7. 
   kevkevinpal commented at 2:46 am on March 23, 2025: contributor

   ACK 288481a
8. ryanofsky assigned ryanofsky on Mar 24, 2025
9. ryanofsky merged this on Mar 24, 2025
10. ryanofsky closed this on Mar 24, 2025

    ---

Contributors
Sjors DrahtBot fjahr kevkevinpal

Labels
Docs