Add EXPERIMENTAL tablet type to vtgate serving path

[ejortegau]

Description

The EXPERIMENTAL tablet type was never included in vtgate's serving path, making it impossible to route queries to EXPERIMENTAL tablets through vtgate. This PR adds EXPERIMENTAL to the serving graph, the SrvKeyspace partition rebuild, the update stream, and the SHOW TABLETS output so vtgate can discover and route queries to EXPERIMENTAL tablets.

After deploying, operators need to run vtctldclient RebuildKeyspaceGraph <keyspace> to regenerate the SrvKeyspace with the new EXPERIMENTAL partition.

Related Issue(s)

Fixes #20114

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

After deploying vtctld with this change, run vtctldclient RebuildKeyspaceGraph <keyspace> for any keyspace that has EXPERIMENTAL tablets. This regenerates the SrvKeyspace to include the EXPERIMENTAL partition. vtgate must also be restarted (or will pick up the new SrvKeyspace via its topo watcher) to begin routing to EXPERIMENTAL tablets.

Optionally add experimental to the arguments of --tablet_types_to_wait if you want vtgate to wait for healthy EXPERIMENTAL tablets at startup.

AI Disclosure

This PR was written with the help of Claude Code.

[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

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Documentation

• Apply the release notes (needs details) label if users need to know about this change.
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Backward compatibility

• Protobuf changes should be wire-compatible.
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• 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.

[Copilot]

Pull request overview

This PR extends Vitess’ serving/visibility logic to treat EXPERIMENTAL tablets as part of the vtgate-serving path (serving graph + SrvKeyspace partitions), so they can be routed to/considered similarly to other serving tablet types.

Changes:

• Include TabletType_EXPERIMENTAL in serving graph and update-stream checks (topo.IsInServingGraph, topo.IsRunningUpdateStream).
• Add EXPERIMENTAL to the set of served tablet types when rebuilding SrvKeyspace partitions (topotools.RebuildKeyspaceLocked).
• Show replication status for EXPERIMENTAL tablets in SHOW VITESS_REPLICATION_STATUS.
• Disable two GitHub workflows by ignoring all branches (appears unrelated to the stated PR purpose).

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
go/vt/vtgate/executor.go	Extends replication-status display filtering to include EXPERIMENTAL tablets.
go/vt/topotools/rebuild_keyspace.go	Adds EXPERIMENTAL to SrvKeyspace partition rebuild served types.
go/vt/topo/tablet.go	Treats EXPERIMENTAL as in the serving graph and eligible for update-stream running checks.
.github/workflows/pr_opened_tasks.yml	Disables PR-opened automation by ignoring all branches.
.github/workflows/error_code_docs_generate.yml	Disables error-code docs generation workflow by ignoring all branches.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

[promptless]

📝 Documentation updates suggested

I've created documentation updates for this PR:

vitessio/website - Added EXPERIMENTAL tablet type documentation:

• Tablet concepts page with SPARE and EXPERIMENTAL type definitions
• FAQ entry for tablet types
• vtgate configuration guide with --tablet-types-to-wait flag documentation

vitessio/vitess - Added changelog entry:

• Documents vtgate EXPERIMENTAL tablet routing capability
• Includes deployment steps (RebuildKeyspaceGraph required)
• Notes optional --tablet-types-to-wait configuration

---

_{🤖 Generated by Promptless}

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.99%. Comparing base (70c7a72) to head (44230a0).
⚠️ Report is 270 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/topo/tablet.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main   #20115       +/-   ##
===========================================
+ Coverage   69.67%   81.99%   +12.32%     
===========================================
  Files        1614      399     -1215     
  Lines      216793    62983   -153810     
===========================================
- Hits       151044    51643    -99401     
+ Misses      65749    11340    -54409     

Flag	Coverage Δ
partial	81.99% <50.00%> (?)

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