Develop a verified repair procedure for pre-marker retry divergence #766

Deferred from the closing review of #753 for declarative sharding (Pro #980). The owner explicitly scoped this root cause out of the closing implementation batch.

Current assessment: The approved release contract enables abort markers by default in 5.4; the separate Harper enablement change is pending. The guide intentionally keeps only the admitted-slot fallback sentence for stores without markers. A tested post-incident detection or repair procedure for those stores is separate; no compensating save or write serialization is authorized.

Owning path: reference/replication/residency.md. Review lines move as the companion branches integrate main; use the linked PR's current source.

Follow-up: Implement and verify the scoped documentation or test improvement without expanding the current runtime contract.

This issue does not reopen #980's approved primary-key-only scope, complete-history requirement, or ban on write serialization. It does not block the current drafts. No release or backport is committed; milestone is intentionally unset. Found through source review and synthetic tests; there is no customer-specific incident evidence.

Triage: P3; effort Low; type Task. Low-priority follow-up: no demonstrated correctness failure or new release requirement. This is deliberately below the parent reliability priority.

Finding IDs: ca3f0675072b, a00453f25016, 43a3811e8a6b.

Review-Deferral: 1d335b8e733e5630 severity=nit category=documentation

Review-Deferral: 2e9ec0a19203dcce severity=minor category=documentation

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