refactor(testing): base tamper specs on StrictBaseModel

[tcoratger]

Motivation

The proof and signature tamper specs in verify_proofs.py (5 classes) and verify_signatures.py (6 classes) inherited raw pydantic.BaseModel — the only models in the package to do so. Every other spec and fixture model inherits StrictBaseModel / CamelModel, which adds:

• frozen=True — no mutation after construction
• strict=True — no implicit type coercion
• extra="forbid" — unknown fields rejected
• camelCase aliasing with populate_by_name=True

A latent inconsistency in a reference codebase.

What this does

Bases all eleven tamper specs on StrictBaseModel. These are immutable value tags applied during generation and consumed by match dispatch — never mutated — so freezing is safe, and all construction sites already pass correctly typed values (ValidatorIndex(...) for typed fields, plain int for int fields), so strict validation accepts them unchanged.

Why it's behavior-preserving

The SignedBlockTamper / SingleMessageTamper / MultiMessageTamper unions include several structurally identical empty models, so the concern was whether validation might coerce one empty tamper into a sibling and break the match dispatch. Verified it does not:

SetProposerIndex           -> SetProposerIndex           preserved=True
ClearFirstAttestationBits  -> ClearFirstAttestationBits  preserved=True
CorruptProof               -> CorruptProof               preserved=True
AppendPhantomAttestation   -> AppendPhantomAttestation   preserved=True
MutateStateRoot            -> MutateStateRoot            preserved=True
SwapFirstTwoAttestations   -> SwapFirstTwoAttestations   preserved=True

Pydantic v2 keeps an exact union-member instance as-is (revalidate_instances defaults to never), so dispatch is unchanged.

Testing

• just check passes (lint, format, ty, codespell, mdformat).
• Fill smoke on verify_proofs + verify_signatures passes; tamper paths emit their distinct rejection reasons (INVALID_BLOCK_PROOF, INVALID_SIGNATURE).
• Confirmed each tamper preserves its exact type through union validation, and frozen rejects post-construction mutation.

🤖 Generated with Claude Code