Module errors 

Compaction error types and failure state guarantees.

This module implements Step 14b of the unified graph architecture.

Failure State Table

The compaction process can fail at various phases. Each error variant has documented state guarantees per the 11-column failure state table:

Error	Phase	Forward CSR	Forward Deltas	Forward Seq	Reverse CSR	Reverse Deltas	Reverse Seq	Committed	Reserved	Counter Reconciled
ConcurrentModification	Phase 2 start	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	N/A
ForwardSwapFailed	Phase 2 forward	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	N/A
ReverseSwapFailed	Phase 2 reverse	ROLLED BACK	ROLLED BACK	ROLLED BACK	UNCHANGED	UNCHANGED	UNCHANGED	RESTORED	RESTORED	YES
CounterReconcileFailed	Phase 2 post-swap	SUCCESS	CLEARED	RESET	SUCCESS	CLEARED	RESET	STALE	UNCHANGED	NO - LOGGED
Interrupted	Phase 1	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	N/A
BuildFailed	Phase 1	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	UNCHANGED	N/A

Invariants

• Forward/reverse stores are ALWAYS consistent after any outcome
• ReverseSwapFailed triggers complete forward rollback before returning
• CounterReconcileFailed is logged but CSR changes persist (no rollback possible)

Two-Phase Commit

Compaction uses a two-phase commit protocol:

1. Phase 1 (Prepare): Build new CSRs offline without holding locks
2. Phase 2 (Commit): Atomic swap with rollback on failure

Failures in Phase 1 leave the system completely unchanged. Failures in Phase 2 before forward swap leave the system unchanged. Failures in Phase 2 after forward swap but before reverse swap trigger rollback.

Structs

PostErrorState

Represents the post-error state for a compaction operation.

SwapPreconditions

Pre-conditions for CSR swap operation.

Enums

BuildFailureReason

Reason for CSR build failure.

CompactionError

Error type for compaction operations.

CompactionPhase

Phase of the compaction process where an error occurred.

ComponentState

State of a component after an error.

CounterReconcileState

State of counter reconciliation after an error.

Direction

Direction indicator for bidirectional operations.

InterruptReason

Reason for compaction interruption.

SwapFailureReason

Reason for CSR swap failure.

SwapPreconditionError

Error from swap pre-condition validation.