[Store] Add P2P hot standby runtime

[skygragon]

Description

Add a P2P-specific hot standby runtime for replaying P2P metadata OpLog entries into P2PStandbyMetadataStore.

This PR introduces P2PHotStandbyService, which reuses the shared OpLog and standby components (StandbyStateMachine, OpLogStoreFactory, OpLogChangeNotifier, and OpLogReplicator) while keeping the orchestration layer P2P-specific. It
intentionally does not inherit from the centralized HotStandbyService because P2P promotion needs P2PStandbyMetadataStore, P2POpLogApplier, and an export shape covering clients, segments, objects, and replicas.

Module

• Transfer Engine (mooncake-transfer-engine)
• Mooncake Store (mooncake-store)
• Mooncake EP (mooncake-ep)
• Mooncake PG (mooncake-pg)
• Integration (mooncake-integration)
• P2P Store (mooncake-p2p-store)
• Python Wheel (mooncake-wheel)
• Common (mooncake-common)
• Mooncake RL (mooncake-rl)
• CI/CD
• Docs
• Other

Type of Change

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

How Has This Been Tested?

Test commands:

./scripts/code_format.sh --base P2P-Mooncake-Store
cmake --build build-verify-noetcd --target p2p_oplog_test -j3
cd build-verify-noetcd && ctest -R "^p2p_oplog_test$" --output-on-failure

Test results:

• Unit tests pass
• Integration tests pass (if applicable)
• Manual testing done (describe below)

p2p_oplog_test passed in the local verification container. The new p2p_hot_standby_service_test.cpp is included in the p2p_oplog_test target.

Checklist

• I have performed a self-review of my own code
• I have formatted my code using ./scripts/code_format.sh
• I have run pre-commit run --all-files and all hooks pass
• I have updated the documentation (if applicable)
• I have added tests to prove my changes are effective
• For changes >500 LOC: I have filed an RFC issue

AI Assistance Disclosure

• No AI tools were used
• AI tools were used (specify below)

AI tools were used to help draft code changes, review diffs, and prepare PR text. The human submitter reviewed the changes and is responsible for them.

[gemini-code-assist]

Code Review

This pull request introduces the P2PHotStandbyService class and its corresponding unit tests to orchestrate P2P hot standby replication and promotion. The feedback highlights a critical data race on P2PStandbyMetadataStore during concurrent metadata exports and background replication, potential resource leaks on Start() and Promote() failures due to uncleaned pointers, and the lack of a reconnection or recovery orchestration loop to handle network interruptions.

Important

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[codecov-commenter]

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Codecov Report

❌ Patch coverage is 81.23324% with 70 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...ake-store/src/ha/oplog/p2p_hot_standby_service.cpp	62.90%	69 Missing ⚠️
...-store/src/ha/oplog/p2p_standby_metadata_store.cpp	96.15%	1 Missing ⚠️

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