br: fix debug decode backupmeta (#56627)

[ti-chi-bot]

This is an automated cherry-pick of #56627

What problem does this PR solve?

Issue Number: close #56296

Problem Summary: We can only see the main backupmeta.json.

What changed and how does it work?

decode the meta file and stats file.

Check List

Tests

• [ ] Unit test
• [ ] Integration test
• [x] Manual test (add detailed scripts or steps below)

$ ls -aF1 /tmp/testbr
./
../
1/
backup.lock
backupmeta
backupmeta.datafile.000000001
backupmeta.schema.000000002
backupmeta.schema.stats.000000110
jsons/

$ ls -aF1 /tmp/testbr/jsons
./
../
backupmeta.datafile.000000001.json
backupmeta.json
backupmeta.schema.000000002.json
backupmeta.schema.stats.000000110.json

backupmeta.datafile.000000001.json

{
  "data_files": [
    {
      "name":"..",
      "sha256":"lu4KiCseT0M6dG2gghZXDwD5WOUOqDMhYKcLHMuDYGA=",
      "start_key":"..",
      "end_key":"..",
      "end_version":452625823236882437,
      "crc64xor":17088955387164552884,
      "total_kvs":1,
      "total_bytes":47,
      "cf":"write",
      "size":1673,
      "cipher_iv":..,
    },
    ...
  ],
}

backupmeta.schema.000000002.json

{
  "schemas":[
    {
      "db": ..,
      "table": ..,
      "crc64xor":4505190652257934775,
      "total_kvs":32,
      "total_bytes":3031,
    },
    ...
  ],
}

backupmeta.schema.stats.000000110.json

{
  "blocks":[
    {
      "physical_id":110,
      "json_table": ..,
    },
}

• [ ] No need to test

  • [ ] I checked and no code files have been changed.

Side effects

• [ ] Performance regression: Consumes more CPU
• [ ] Performance regression: Consumes more Memory
• [ ] Breaking backward compatibility

Documentation

• [ ] Affects user behaviors
• [ ] Contains syntax changes
• [ ] Contains variable changes
• [ ] Contains experimental features
• [ ] Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[codecov[bot]]

Codecov Report

:x: Patch coverage is 48.54369% with 106 lines in your changes missing coverage. Please review. :warning: Please upload report for BASE (release-8.5@c703402). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #64786   +/-   ##
================================================
  Coverage               ?   77.1850%           
================================================
  Files                  ?       1681           
  Lines                  ?     467426           
  Branches               ?          0           
================================================
  Hits                   ?     360783           
  Misses                 ?      84565           
  Partials               ?      22078           

Flag	Coverage Δ
integration	51.1126% <16.5048%> (?)
unit	72.1727% <46.6019%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.9278% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	65.6162% <0.0000%> (?)

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[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: BornChanger, Leavrth

The full list of commands accepted by this bot can be found here.

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Needs approval from an approver in each of these files:

• ~~br/OWNERS~~ [BornChanger,Leavrth]

Approvers can indicate their approval by writing /approve in a comment Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2025-12-13 09:58:09.562833789 +0000 UTC m=+1294234.376611351: :ballot_box_with_check: agreed by Leavrth.
• 2025-12-13 12:31:16.633152118 +0000 UTC m=+1303421.446929690: :ballot_box_with_check: agreed by BornChanger.

[Leavrth]

/retest