[Icedcoco]

Description

HA promotion currently preserves an object's replicas but drops its optional object checksum. This change carries ObjectPart::checksum through OpLog payloads, standby metadata and snapshots, then restores it when publishing recovered objects. It covers the existing checksum diagnostic feature; it does not change checksum calculation or repair historical entries that never stored a checksum.

The schema addition uses a compatible field so readers accept older payloads and snapshots. Older records restore with an absent checksum, and older writers still discard the new field, so all writers must be upgraded for checksum continuity.

Related: #3140 added optional object checksum diagnostics and explicitly left HA OpLog continuity out of scope. This PR addresses that HA gap.

Suggested Merge Priority

• P0 — Urgent
• P1 — High
• P2 — Normal
• P3 — Low

Module

• Mooncake Store (mooncake-store)

Type of Change

• Bug fix
• New feature
• Refactor
• Breaking change
• Documentation update
• Performance improvement
• Other

How Has This Been Tested?

Test commands:

/tmp/mooncake-build-fix-ha-001-default/mooncake-store/tests/object_part_test --gtest_color=no
/tmp/mooncake-build-fix-ha-001-default/mooncake-store/tests/session_tag_test --gtest_color=no
/tmp/mooncake-build-fix-ha-001-default/mooncake-store/tests/batch_oplog_snapshot_codec_test --gtest_color=no
/tmp/mooncake-build-fix-ha-001-default/mooncake-store/tests/master_service_ha_test --gtest_color=no

Test results:

• Unit tests pass: 8/8, 10/10, and 4/4 respectively
• HA tests pass: 131/131
• Manual live-cluster failover test

Checklist

• I have performed a self-review of my own code
• I have formatted my code using clang-format 20 through the staged-file pre-commit hook
• I have run pre-commit on the files changed in this PR and all hooks pass
• I have updated the documentation (not applicable; no user-facing behavior or API changed)
• I have added tests to prove my changes are effective
• For changes >500 LOC: I have filed an RFC issue (not applicable)

AI Assistance Disclosure

• No AI tools were used
• AI tools were used: assisted with code investigation, implementation, tests, and PR preparation. The human submitter is responsible for reviewing and understanding every changed line.