Merge bitcoin/bitcoin#25574: validation: Improve error handling when VerifyDB dosn't finish successfully

0af16e7134459e0820ab95d751093876c1ec4c6d doc: add release note for #25574 (Martin Zumsande)
57ef2a4812f443b2d734f43cebf3ef5038da83f2 validation: report if pruning prevents completion of verification (Martin Zumsande)
0c7785bb2540b69564104767d38342704230cbc2 init, validation: Improve handling if VerifyDB() fails due to insufficient dbcache (Martin Zumsande)
d6f781f1cfcbc2c2ad5ee289a0642ed00386d013 validation: return VerifyDBResult::INTERRUPTED if verification was interrupted (Martin Zumsande)
6360b5302d2675788de5c4a28ea77d823f6d809e validation: Change return value of VerifyDB to enum type (Martin Zumsande)

Pull request description:

  `VerifyDB()` can fail to complete due to insufficient dbcache at the level 3 checks. This PR improves the error handling in this case in the following ways:
  - The rpc `-verifychain` now returns false if the check can't be completed due to insufficient cache
  - During init, we only log a warning if the default values for `-checkblocks` and `-checklevel` are taken and the check doesn't complete. However, if the user actively specifies one of these args, we return with an InitError if we can't complete the check.

  This PR also changes `-verifychain` RPC to return `false` if the verification didn't finish due to missing block data (pruning) or due to being interrupted by the node being shutdown.

  Previously, this PR also included a fix for a possible assert during verification - this was done in #27009 (now merged).

ACKs for top commit:
  achow101:
    ACK 0af16e7134459e0820ab95d751093876c1ec4c6d
  ryanofsky:
    Code review ACK 0af16e7134459e0820ab95d751093876c1ec4c6d. Only small suggested changes since the last review, like renaming some of the enum values. I did leave more suggestions, but they are not very important and could be followups
  john-moffett:
    ACK 0af16e7134459e0820ab95d751093876c1ec4c6d
  MarcoFalke:
    lgtm re-ACK 0af16e7134459e0820ab95d751093876c1ec4c6d 🎚

Tree-SHA512: 84b4f767cf9bfbafef362312757c9bf765b41ae3977f4ece840e40c52a2266b1457832df0cdf70440be0aac2168d9b58fc817238630b0b6812f3836ca950bc0e

1 files changed, 13 insertions, 0 deletions

diff --git a/doc/release-notes-25574.md b/doc/release-notes-25574.md
new file mode 100644
index 0000000000..312a99d95b
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+++ b/doc/release-notes-25574.md
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+Updated settings
+----------------
+
+If the `-checkblocks` or `-checklevel` options are explicitly provided by the
+user, but the verification checks cannot be completed due to an insufficient
+dbcache, Bitcoin Core will now return an error at startup. (#25574)
+
+RPC
+---
+The `-verifychain` RPC will now return `false` if the checks didn't fail,
+but couldn't be completed at the desired depth and level. This could be due
+to missing data while pruning, due to an insufficient dbcache or due to
+the node being shutdown before the call could finish. (#25574)