branch-4.1: [fix](cloud) Correct cumulative point advancement when enable parallel cumulative compaction (#65915)

[mymeiyi]

pick #65915

[hello-stephen]

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Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
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[mymeiyi]

run buildall

[Copilot]

🔵 Needs a closer look

The change touches core compaction correctness across BE/meta-service with parallel/concurrent behavior, so it warrants final human verification despite tests and only minor review nits found.

Pull request overview

Backports the cloud compaction fix from #65915 to ensure cumulative_point is advanced safely when parallel cumulative compactions can finish out of order, adding validation/guardrails in meta-service and tightening BE-side application rules with expanded test coverage.

Changes:

• Add meta-service logic to validate/ignore stale cumulative-point proposals and update tablet stats more defensively during compaction FINISH.
• Update BE compaction flows to attach compaction counter snapshots and only apply cumulative results when the response counter is the expected “next” value (otherwise force a tablet sync).
• Add/extend unit tests covering legacy vs current behavior, parallel ordering, counter snapshot handling, and sync-forcing scenarios.

File summaries

File	Description
cloud/test/meta_service_job_test.cpp	Adds helpers and multiple regression tests for parallel/legacy cumulative-point advancement and counter validation.
cloud/src/meta-service/meta_service_job.cpp	Introduces cumulative-point acceptance logic and adds validation around cumulative counter presence in FINISH.
be/test/storage/compaction/cloud_index_change_compaction_test.cpp	Adds test ensuring base compaction response with newer cumulative point forces a sync (without mutating local point).
be/test/cloud/cloud_compaction_test.cpp	Adds comprehensive tests for applying cumulative results, parallel pick behavior, delete handling, and sync triggering.
be/src/storage/compaction/compaction.h	Declares CloudCompactionMixin::should_apply_cumulative_compaction_result (header-lock required).
be/src/storage/compaction/compaction.cpp	Implements the “apply only next cumulative result, else force sync” gating logic.
be/src/cloud/cloud_index_change_compaction.cpp	Includes counter snapshots in jobs and uses the new gating logic for cumulative result application; forces sync on newer point from base response.
be/src/cloud/cloud_cumulative_compaction.h	Adds parallel-mode state/snapshots and updates cumulative-point update API.
be/src/cloud/cloud_cumulative_compaction.cpp	Implements conflict-window-aware picking/point advancement, stable execution mode snapshotting, and counter snapshot propagation.
be/src/cloud/cloud_base_compaction.cpp	Forces sync when meta-service reports a newer cumulative point after base compaction.

Review details

• Files reviewed: 10/10 changed files
• Comments generated: 1
• Review effort level: Lite

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[hello-stephen]

Cloud UT Coverage Report

Increment line coverage 91.76% (78/85) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	78.35% (1943/2480)
Line Coverage	64.92% (34611/53310)
Region Coverage	52.48% (33229/63320)
Branch Coverage	55.12% (10221/18544)