Always emit bump events, even when fees are sufficient

[wvanlint]

Currently, the anchor commitment bump events are bypassed when the commitment transaction has sufficient fees. However, this makes it difficult for users to defer force-closures to a trusted party (such as an LSP) while not maintaining reserves. Broadcasting a commitment transaction without maintaining reserves would make HTLCs unclaimable against that commitment transaction.

In this change, anchor commitment bump events will always be emitted so users can capture and choose not to process them.

Fixes #3496.

[ldk-reviews-bot]

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[wpaulino]

Basically LGTM, any reason why it's draft?

[codecov]

Codecov Report

❌ Patch coverage is 83.95062% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.94%. Comparing base (192618b) to head (d99e59b).
⚠️ Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/monitor_tests.rs	72.72%	3 Missing and 3 partials ⚠️
lightning/src/ln/reorg_tests.rs	84.61%	3 Missing and 1 partial ⚠️
lightning/src/ln/functional_test_utils.rs	85.71%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4001   +/-   ##
=======================================
  Coverage   88.93%   88.94%           
=======================================
  Files         174      174           
  Lines      124593   124642   +49     
  Branches   124593   124642   +49     
=======================================
+ Hits       110813   110861   +48     
- Misses      11283    11287    +4     
+ Partials     2497     2494    -3     

Flag	Coverage Δ
fuzzing	22.17% <0.00%> (-0.01%)	⬇️
tests	88.77% <83.95%> (+<0.01%)	⬆️

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[wvanlint]

Basically LGTM, any reason why it's draft?

Ah, I was mainly waiting for CI to complete successfully, marked ready for review now.

[ldk-reviews-bot]

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[TheBlueMatt]

Ah! This actually seems like a bugfix. I was curious why the tests were changing at all, it looks like if we do the event-bypass we won't properly bump the commitment-broadcast feerate after every few blocks like we should, at least in some cases.

In update_claims_view_from_requests (and update_claims_view_from_matched_txn) we set_feerate on the package to the feerate returned by generate_claim. In the bypass code removed here, we return a selected feerate of 0, rather than the actually-used feerate (or the target feerate, which I think we should really be using). Then, if the feerate is 0, we'll consider it "no previous feerate" in the bump logic and just use the new fee estimator rather than bumping 25% if we don't see confirmation. This isn't that critical as we'll still increase fee if the fee estimator goes up, and in any case where the fee estimator goes up enough to jump beyond the by pass case we'll immediately start the regular 25%-ever-few-blocks bumping we want anyway, but it does make us rely on the user's fee estimator more than we want to.