Add opt-in isolated SolrCloud verification for SPLITSHARD and MIGRATE #232

Context

SPLITSHARD and MIGRATE have typed V1 parameter/response contracts and serialization/type fixtures, but no runtime verification. The coverage matrix intentionally excludes them from shared CI because they are long-running and can affect routing or data placement.

Scope

• Design an opt-in isolated SolrCloud test environment with disposable collections and controlled compositeId routing.
• Verify SPLITSHARD and MIGRATE semantics, completion/status behavior, and resulting shard/data placement.
• Ensure cleanup and failure recovery cannot affect shared fixtures or external Solr clusters.
• If safe automation is impractical, retain explicit non-certification and document a reproducible manual verification procedure.

Acceptance criteria

• Tests are opt-in and cannot run against the default/shared integration collection.
• Setup is guarded by explicit opt-in, loopback-only endpoint, SolrCloud, and multi-node requirements; fixtures create unique disposable collections, require a one-shard split source, and require an empty migration target.
• Behavior is asserted from resulting cluster state and data placement (active child shards and split read-back; migrated target document read-back).
• Timeout and failure handling are documented; async status is polled with a bounded timeout, status records are deleted on completion, and a failed cleanup requires discarding the ephemeral cluster. Live cancellation/partial-operation recovery are explicitly not certified.
• Compatibility status changes only for versions actually tested.

Implementation update (2026-11-04)

• PR test(solr): verify replication and shard lifecycle operations #253 adds an opt-in, loopback-only two-node SolrCloud workflow for SPLITSHARD and MIGRATE, using unique disposable collections, asynchronous status polling, post-operation state/read-back assertions, and cleanup.
• The workflow is wired to workflow_dispatch and the enable_destructive_solrcloud_tests input. It is deliberately not run in ordinary PR CI.
• The opt-in workflow still needs a manual dispatch and successful per-version evidence. Until then, compatibility remains unverified and this issue stays open.

Implementation status after PR #253 merge (2026-11-04)

• PR test(solr): verify replication and shard lifecycle operations #253 is merged. The opt-in test harness and workflow are now on master.
• Four safety/behavior/documentation acceptance criteria are implemented. The remaining gate is execution of the manual workflow_dispatch with enable_destructive_solrcloud_tests=true and successful per-version evidence for Solr 8.11.4, 9.11.0, and 10.1.0.
• The available GitHub integration does not expose a workflow-dispatch action, so no run has been started from this session. Compatibility remains unverified until a repository maintainer manually runs the workflow and records the result.