CBG-4625: test-only additional ISGR peers now take same subprotocol

[torcolvin]

CBG-4625: test-only additional ISGR peers now take same subprotocol

addActiveRT built extra active nodes without ISGRSupportedBLIPSubprotocols, so in revtree subtests node 2 negotiated CBMobile_4, causing occaisonal downstream failure. A replication
reassigned to it re-pulled already-replicated docs over V4 and wrote them as new revs, adding sequences and breaking the "exactly N changes since X" assertions (TestReplicationHeartbeatRemoval flake). If the replication didn't get reassigned, the test would pass.

• Do a magic dance of recreating open channel for DatabaseConfig.ServerContextHasStarted and closing it after setting subprotocol.
• DatabaseConfig is a mutable object when adding to a Database, so removed RestTesterConfig from places in order to add the specific options.
• Now match the SyncFn and other parameters for second RestTester

Pre-review checklist

• Logging sensitive data? Make sure it's tagged (e.g. base.UD(docID), base.MD(dbName))
• Updated relevant information in the API specifications (such as endpoint descriptions, schemas, ...) in docs/api

Integration Tests

• https://jenkins.sgwdev.com/job/SyncGatewayIntegration/1106/

[factory-droid]

Droid finished @torcolvin's task —— View job

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LGTM, no high-confidence actionable issues found in the changes. The ISGR test harness updates should make BLIP subprotocol negotiation consistent across additional active nodes and reduce flakiness.

[Copilot]

Pull request overview

This PR stabilizes ISGR-related test runs by ensuring additional (test-only) active peers in an ISGR “cluster” negotiate the same BLIP subprotocol as the primary active peer, preventing occasional protocol mismatches that caused flaky replication assertions.

Changes:

• Added a test-only RestTesterConfig option to force ISGR BLIP subprotocols per node, and delayed ISGR replication startup until the subprotocol override is applied.
• Refactored ISGR test peer setup to build per-node RestTesterConfig (avoiding mutation/reuse issues) and to support adding additional active nodes consistently.
• Updated replicator/BLIP tests to use the new peers helper and to explicitly pass supported BLIP subprotocols where active replicators are constructed directly.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
rest/utilities_testing.go	Adds ISGRSupportedBLIPSubprotocols and delays replication startup so the override is applied before ISGR begins.
rest/utilities_testing_isgr.go	Refactors ISGR peer setup to generate per-node configs, share buckets correctly, and support adding additional active peers with consistent subprotocols.
rest/replicatortest/replicator_test.go	Switches tests to the new peers helper and threads supported subprotocols into direct replicator configs where needed.
rest/replicatortest/replicator_test_legacy_rev_test.go	Updates legacy revision tests to use the new peers helper and delta-sync option handling.
rest/replicatortest/replicator_test_helper.go	Removes the old addActiveRT helper in favor of TestISGRPeers.AddActiveRT.
rest/replicatortest/replicator_revtree_test.go	Updates revtree tests to use peers helper and to pass supported BLIP subprotocols to active replicators.
rest/replicatortest/replicator_conflict_test.go	Updates conflict tests to use peers helper and additional active node creation via AddActiveRT.
rest/replicatortest/replicator_collection_test.go	Updates collection tests to use the new peers helper return type.
rest/blip_api_crud_test.go	Updates BLIP CRUD test to use the new peers helper return type.

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