[iloveeyjafjalla]

Which Issue(s) This PR Fixes

• Fixes [Bug] AdminSendMessage maps a FIFO message group to a different queue than the data plane #11356

Brief Description

AdminSendMessage resolved the write queue of a message group with
Math.floorMod(shardingKey.hashCode(), queues.size()), while the gRPC data plane resolves it with Guava's
consistent hash (SendMessageActivity.java:414). The two functions disagree for the same group and queue count —
for message group groupA-fifo over 3 writable queues, floorMod picks queue 2 and consistentHash picks
queue 0 — so a message injected through the admin surface could land on a queue that the group's producers never
write to. Per-group FIFO order only holds within a single queue, so the group's messages could be consumed out
of order, and the RPC still answered OK, so nothing told the operator the group was split.

selectQueue's javadoc states the intent ("A FIFO message must keep going to the queue its message group hashes
to") and docs/proxy-admin.md §D4 documents this path as "system properties honoured for timer / FIFO messages",
so the mapping is meant to match the data plane.

The change makes the admin path use the same hash function the data plane uses. Nothing else changes: the
no-message-group branch keeps spreading over the writable queues.

How Did You Test This Change?

New unit test ProxyAdminGrpcServiceTest#adminSendMessageRoutesMessageGroupToTheDataPlaneQueueTest: it captures
the QueueSelector the RPC hands to MessagingProcessor#sendMessage, runs it against a mocked MessageQueueView
with 3 writable queues, and asserts the selected queue is the one the data plane's formula picks for that group.
It also asserts the two formulas differ for the test key, so the test cannot silently pass if the old mapping
comes back.

Results on Temurin JDK 8 (same JDK as CI), base 9ea2ccdc2 plus this patch:

• before the fix, the new test fails: expected:<...queueId=0...> but was:<...queueId=2...>
• after the fix: Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
• whole class: Tests run: 61, Failures: 0, Errors: 0, Skipped: 0 (mvn -B -ntp -pl proxy -am test -Dtest=ProxyAdminGrpcServiceTest)

This change was prepared with AI assistance (analysis, patch and test drafting); the diff and every result above
were reproduced locally by running the module's tests against the base commit and the patched tree.

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Review by github-manager-bot

Summary

Fix admin path queue hash mismatch: use Hashing.consistentHash instead of Math.floorMod so admin-injected messages land on the same queue as the data plane, preserving FIFO ordering.

Findings

• [Info] ProxyAdminGrpcService.java:1436 — The 1-line fix correctly aligns the admin path with the data plane's hash function (SendMessageActivity.java:414). The no-message-group branch (random selection) is unchanged, which is correct.
• [Info] ProxyAdminGrpcServiceTest.java — The new test is well-designed: it captures the QueueSelector, runs it against mocked queues, and asserts the selected queue matches the data plane's formula. The assertion that the two formulas differ for the test key (assertNotEquals) prevents silent regression if the old mapping comes back.

Suggestions

No blocking concerns. This is a minimal, targeted fix with clear problem description and solid test coverage.

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Automated review by github-manager-bot