seaweedfs/sw-block/docs/archive/design/a5-a8-traceability.md

A5-A8 Acceptance Traceability

Date: 2026-03-29 Status: historical evidence traceability

Purpose

Map each acceptance criterion to specific executable evidence. Two evidence layers:

• Simulator (distsim): protocol-level proof
• Prototype (enginev2): ownership/session-level proof

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A5: Non-Convergent Catch-Up Escalates Explicitly

Must prove: tail-chasing or failed catch-up does not pretend success.

Pass condition: explicit CatchingUp → NeedsRebuild transition.

Evidence	Test	File	Layer	Status
Tail-chasing converges or aborts	TestS6_TailChasing_ConvergesOrAborts	cluster_test.go	distsim	PASS
Tail-chasing non-convergent → NeedsRebuild	TestS6_TailChasing_NonConvergent_EscalatesToNeedsRebuild	phase02_advanced_test.go	distsim	PASS
Catch-up timeout → NeedsRebuild	TestP03_CatchupTimeout_EscalatesToNeedsRebuild	phase03_timeout_test.go	distsim	PASS
Reservation expiry aborts catch-up	TestReservationExpiryAbortsCatchup	cluster_test.go	distsim	PASS
Flapping budget exceeded → NeedsRebuild	TestP02_S5_FlappingExceedsBudget_EscalatesToNeedsRebuild	phase02_advanced_test.go	distsim	PASS
Catch-up converges or escalates (I3)	TestI3_CatchUpConvergesOrEscalates	phase045_crash_test.go	distsim	PASS
Catch-up timeout in enginev2	TestE2E_NeedsRebuild_Escalation	p2_test.go	enginev2	PASS

Verdict: A5 is well-covered. Both simulator and prototype prove explicit escalation. No pretend-success path exists.

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A6: Recoverability Boundary Is Explicit

Must prove: recoverable vs unrecoverable gap is decided explicitly.

Pass condition: recovery aborts when reservation/payload availability is lost; rebuild is explicit fallback.

Evidence	Test	File	Layer	Status
Reservation expiry aborts catch-up	TestReservationExpiryAbortsCatchup	cluster_test.go	distsim	PASS
WAL GC beyond replica → NeedsRebuild	TestI5_CheckpointGC_PreservesAckedBoundary	phase045_crash_test.go	distsim	PASS
Rebuild from snapshot + tail	TestReplicaRebuildFromSnapshotAndTail	cluster_test.go	distsim	PASS
Smart WAL: resolvable → unresolvable	TestP02_SmartWAL_RecoverableThenUnrecoverable	phase02_advanced_test.go	distsim	PASS
Time-varying payload availability	TestP02_SmartWAL_TimeVaryingAvailability	phase02_advanced_test.go	distsim	PASS
RecoverableLSN is replayability proof	RecoverableLSN() in storage.go	storage.go	distsim	Implemented
Handshake outcome: NeedsRebuild	TestExec_HandshakeOutcome_NeedsRebuild_InvalidatesSession	execution_test.go	enginev2	PASS

Verdict: A6 is covered. Recovery boundary is decided by explicit reservation + recoverability check, not by optimistic assumption. RecoverableLSN() verifies contiguous WAL coverage.

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A7: Historical Data Correctness Holds

Must prove: recovered data for target LSN is historically correct; current extent cannot fake old history.

Pass condition: snapshot + tail rebuild matches reference; current-extent reconstruction of old LSN fails correctness.

Evidence	Test	File	Layer	Status
Snapshot + tail matches reference	TestReplicaRebuildFromSnapshotAndTail	cluster_test.go	distsim	PASS
Historical state not reconstructable after GC	TestA7_HistoricalState_NotReconstructableAfterGC	phase045_crash_test.go	distsim	PASS
CanReconstructAt() rejects faked history	CanReconstructAt() in storage.go	storage.go	distsim	Implemented
Checkpoint does not leak applied state	TestI2_CheckpointDoesNotLeakAppliedState	phase045_crash_test.go	distsim	PASS
Extent-referenced resolvable records	TestExtentReferencedResolvableRecordsAreRecoverable	cluster_test.go	distsim	PASS
Extent-referenced unresolvable → rebuild	TestExtentReferencedUnresolvableForcesRebuild	cluster_test.go	distsim	PASS
ACK'd flush recoverable after crash (I1)	TestI1_AckedFlush_RecoverableAfterPrimaryCrash	phase045_crash_test.go	distsim	PASS

Verdict: A7 is now covered with the Phase 4.5 crash-consistency additions. The critical gap ("current extent cannot fake old history") is proven by CanReconstructAt() + TestA7_HistoricalState_NotReconstructableAfterGC.

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A8: Durability Mode Semantics Are Correct

Must prove: best_effort, sync_all, sync_quorum behave as intended under mixed replica states.

Pass condition: sync_all strict, sync_quorum commits only with true durable quorum, invalid topology rejected.

Evidence	Test	File	Layer	Status
sync_quorum continues with one lagging	TestSyncQuorumContinuesWithOneLaggingReplica	cluster_test.go	distsim	PASS
sync_all blocks with one lagging	TestSyncAllBlocksWithOneLaggingReplica	cluster_test.go	distsim	PASS
sync_quorum mixed states	TestSyncQuorumWithMixedReplicaStates	cluster_test.go	distsim	PASS
sync_all mixed states	TestSyncAllBlocksWithMixedReplicaStates	cluster_test.go	distsim	PASS
Barrier timeout: sync_all blocked	TestP03_BarrierTimeout_SyncAll_Blocked	phase03_timeout_test.go	distsim	PASS
Barrier timeout: sync_quorum commits	TestP03_BarrierTimeout_SyncQuorum_StillCommits	phase03_timeout_test.go	distsim	PASS
Promotion uses RecoverableLSN	EvaluateCandidateEligibility()	cluster.go	distsim	Implemented
Promoted replica has committed prefix (I4)	TestI4_PromotedReplica_HasCommittedPrefix	phase045_crash_test.go	distsim	PASS

Verdict: A8 is well-covered. sync_all is strict (blocks on lagging), sync_quorum uses true durable quorum (not connection count). Promotion now uses RecoverableLSN() for committed-prefix check.

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Summary

Criterion	Simulator Evidence	Prototype Evidence	Status
A5 (catch-up escalation)	6 tests	1 test	Strong
A6 (recoverability boundary)	6 tests + RecoverableLSN()	1 test	Strong
A7 (historical correctness)	7 tests + CanReconstructAt()	—	Strong (new in Phase 4.5)
A8 (durability modes)	7 tests + RecoverableLSN()	—	Strong

Total executable evidence: 26 simulator tests + 2 prototype tests + 2 new storage methods.

All A5-A8 acceptance criteria have direct test evidence. No criterion depends solely on design-doc claims.

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Still Open (Not Blocking)

Item	Priority	Why not blocking
Predicate exploration / adversarial search	P2	Manual scenarios already cover known failure classes
Catch-up convergence under sustained load	P2	I3 proves escalation; load-rate modeling is optimization
A5-A8 in a single grouped runner view	P3	Traceability doc serves as grouped evidence for now