[vsimko]

Summary

• Add an isolated two-core ReplicationHandler integration test using disposable leader and follower cores.
• Use the canonical fetchindex / abortfetch command names across Solr 8.11.4, 9.11.0, and 10.1.0.
• Verify a committed leader document becomes searchable on the follower, with deterministic core cleanup and timeout diagnostics.
• Add an opt-in, loopback-only two-node SolrCloud workflow for SPLITSHARD and MIGRATE using uniquely created collections, asynchronous status polling, and post-operation shard/document read-back.
• Correct ReplicationHandler compatibility documentation and related API coverage documentation.

Validation status

• CI run #640 passed all 30/30 jobs on head 18076cb6d4b1ee11fa115bc216777b4b0459996b.
• This includes unit/type tests and integration, cloud-integration, and security-integration jobs for Solr 8.11.4, 9.11.0, and 10.1.0 on Node.js 20, 22, and 24.
• The earlier follower-to-leader BasicAuth HTTP 401 is resolved by passing the documented follower connection credentials through fetchindex custom parameters. Credentials are not embedded in the leader URL.
• The leader/follower fetch/read-back test is now runtime-verified across the pinned matrix. Live-transfer abort and polling lifecycle behavior remain explicitly unverified and are not claimed by this PR.
• SPLITSHARD and MIGRATE remain runtime-unverified until the manual opt-in workflow is dispatched and successful per-version evidence is recorded. The workflow is excluded from normal PR CI.

Related issues: #232, #238.

[vsimko]

CI run #635 confirms the remaining replication failure is specifically the follower-to-leader request returning HTTP 401 (IndexFetcher ... command=indexversion). The previous test supplied BasicAuth credentials only in the follower's persisted Config API handler config. I have updated the test to also pass the documented follower connection options (httpBasicAuthUser / httpBasicAuthPassword) as fetchindex custom parameters, while keeping the credentials out of the leader URL and logs. New head: 18076cb6d4b1ee11fa115bc216777b4b0459996b. The next gate is a fresh full PR matrix; no issues are being closed until the matrix and opt-in SolrCloud run provide evidence.