show vitess_keyspaces should not trip over deleted keyspaces

[nickvanw]

Description

When a keyspace is deleted, SHOW VITESS_SHARDS can fail because the keyspace name is still in the serving graph cache, but fetching its shards returns a topo.NoNode error. The error was being wrapped with vterrors.Errorf which converted it to Code_UNKNOWN, making it indistinguishable from real errors.

This PR changes GetKeyspaceShards to use vterrors.Wrapf instead, preserving the underlying error type. Then in ShowShards, we check for topo.NoNode errors and skip those keyspaces rather than failing the entire query.

Added a unit test to verify deleted keyspaces are handled gracefully.

Related Issue(s)

Closes #19080

Related to #7955

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

Deployment Notes

N/A

AI Disclosure

This PR was written in concert with Claude Code and Opus 4.5 - especially the test generation.

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

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• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

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• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

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Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.90%. Comparing base (7a3acd5) to head (51c8652).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #19055   +/-   ##
=======================================
  Coverage   69.90%   69.90%           
=======================================
  Files        1612     1612           
  Lines      215817   215821    +4     
=======================================
+ Hits       150865   150869    +4     
  Misses      64952    64952           

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