Module error 

Error enums for dig-block.

• Tier 1 BlockError (structural): ERR-001, NORMATIVE § ERR-001.
• Tier 2 /3 BlockError (execution / state): ERR-002, NORMATIVE § ERR-002.
• CheckpointError (checkpoints): ERR-003, SPEC §4.2.
• BuilderError (block construction): ERR-004, SPEC §6.5.
• SignerBitmapError / ReceiptError: ERR-005, SPEC §4.3–4.4.
• Crate spec: SPEC §4.1–4.2 — error taxonomy and validator layering.

Enums

BlockError

Block validation failures across three tiers on one enum (ERR-001, ERR-002).

BuilderError

Block assembly failures while mutating crate::BlockBuilder (budgets, slash payloads, signing, v2 DFSP preconditions).

CheckpointError

Checkpoint lifecycle failures: submission, scoring, epoch alignment, and finalization (ERR-003).

ReceiptError

Receipt list / indexer failures for execution receipts (ERR-005, SPEC §4.4).

SignerBitmapError

Signer bitmap subsystem failures: index bounds, wire length, and validator-set cardinality (ERR-005).