VReplication: Sync in-memory workflow state metric on workflow read

[mcrauwel]

Description

Use the stored state of the workflow as source of truth for the stats/metrics reporting.

Related Issue(s)

• Fixes: Bug Report: VReplication: stream state metric falsely reports Error when _vt.vreplication UPDATE fails #20012

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

AI Disclosure

I worked with Claude Opus 4.7 on this

[vitess-bot]

Review Checklist

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[Copilot]

Pull request overview

This PR fixes a VReplication observability/correctness issue where in-memory stream state metrics could advance to Error even when the corresponding _vt.vreplication row update fails (e.g., MySQL is read_only during reparent), causing operators to see misleading stream state in metrics and /debug/vars.

Changes:

• Move in-memory State metric updates to occur only after the _vt.vreplication UPDATE succeeds (for both vreplicator and BinlogPlayer paths).
• Add unit tests ensuring state metrics do not advance when the DB update fails.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
go/vt/vttablet/tabletmanager/vreplication/vreplicator.go	Defers vr.stats.State update until after the DB UPDATE succeeds.
go/vt/vttablet/tabletmanager/vreplication/vreplicator_test.go	Adds a test ensuring setState doesn’t advance the metric on DB error.
go/vt/binlog/binlogplayer/binlog_player.go	Defers blp.blplStats.State update until after the DB UPDATE succeeds.
go/vt/binlog/binlogplayer/binlog_player_test.go	Adds a test ensuring setVReplicationState doesn’t advance the metric on DB error.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.82%. Comparing base (70c7a72) to head (e07ae8d).
⚠️ Report is 221 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main   #20013       +/-   ##
===========================================
+ Coverage   69.67%   73.82%    +4.15%     
===========================================
  Files        1614       34     -1580     
  Lines      216793     5845   -210948     
===========================================
- Hits       151044     4315   -146729     
+ Misses      65749     1530    -64219     

Flag	Coverage Δ
partial	73.82% <100.00%> (?)

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.