### Please describe the problem.

I ran git annex fsck --json. I have some files that are lacking numcopies. I get output in stderr, but no error details in the json body.

For example:

{"command":"fsck","success":false,"key":"SHA256E-s165540--ddcf7ce58593667e1b836e2a7f28a9f5227f3d9ba46cf8f98c7ab9dd26ef1896.jpg","error-messages":[],"file":"2022/12/04/chandrian_10:06:41.jpg","dead":[],"untrusted":[],"input":["2022/12/04/chandrian_10:06:41.jpg"]}
  Only 2 of 5 trustworthy copies exist of 2022/12/04/chandrian_11:05:20.jpg
  Back it up with git-annex copy.


It would be great if error-messages contained all the details for failures. Thank you


### What steps will reproduce the problem?

* create a new repo
* annex a file
* set numcopies to 2 or whatever
* git annex fsck --json


### What version of git-annex are you using? On what operating system?

I'm on Fedora 37.

git annex version
git-annex version: 10.20221103
build flags: Assistant Webapp Pairing Inotify DBus DesktopNotify TorrentParser MagicMime Feeds Testsuite S3 WebDAV
dependency versions: aws-0.22 bloomfilter-2.0.1.0 cryptonite-0.29 DAV-1.3.4 feed-1.3.2.0 ghc-8.10.7 http-client-0.6.4.1 persistent-sqlite-2.13.1.0 torrent-10000.1.1 uuid-1.3.15 yesod-1.6.2
key/value backends: SHA256E SHA256 SHA512E SHA512 SHA224E SHA224 SHA384E SHA384 SHA3_256E SHA3_256 SHA3_512E SHA3_512 SHA3_224E SHA3_224 SHA3_384E SHA3_384 SKEIN256E SKEIN256 SKEIN512E SKEIN512 BLAKE2B256E BLAKE2B256 BLAKE2B512E BLAKE2B512 BLAKE2B160E BLAKE2B160 BLAKE2B224E BLAKE2B224 BLAKE2B384E BLAKE2B384 BLAKE2BP512E BLAKE2BP512 BLAKE2S256E BLAKE2S256 BLAKE2S160E BLAKE2S160 BLAKE2S224E BLAKE2S224 BLAKE2SP256E BLAKE2SP256 BLAKE2SP224E BLAKE2SP224 SHA1E SHA1 MD5E MD5 WORM URL X*
remote types: git gcrypt p2p S3 bup directory rsync web bittorrent webdav adb tahoe glacier ddar git-lfs httpalso borg hook external
operating system: linux x86_64
supported repository versions: 8 9 10
upgrade supported from repository versions: 0 1 2 3 4 5 6 7 8 9 10
local repository version: 10


### Please provide any additional information below.

[[!format sh """
# If you can, paste a complete transcript of the problem occurring here.
# If the problem is with the git-annex assistant, paste in .git/annex/daemon.log


# End of transcript or log.
"""]]

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

Yes! Git annex is amazing and is managing over 10 TB of data across 5 git annexes and around 10 hard drives. No data loss this entire time -- over 8 years.

> [[notabug|done]]; see my comment --[[Joey]]
