fix(nitro-verifier): add Unknown sentinel to VerificationResult for fail-closed default

[leopoldjoy]

Summary

• Adds Unknown as index 0 in the VerificationResult enum so that uninitialized enum variables default to a failure state instead of Success
• Follows the defensive design principle that the zero/default value should be the most restrictive state (fail-closed), preventing any future code path from accidentally treating an uninitialized verification result as a successful attestation

Details

In Solidity, the default value for any uninitialized enum is 0. Previously, Success was at index 0, meaning an uninitialized VerificationResult would silently equal "success" — a classic fail-open anti-pattern in security-sensitive code.

While no live vulnerability exists today (all current code paths fully initialize the result before checking it), the enum ordering is fragile against future modifications. For example:

• A VerifierJournal allocated via new VerifierJournal[](n) would have result default to Success before assignment
• A partially decoded struct or forgotten assignment could silently pass != VerificationResult.Success checks

The new enum ordering:

enum VerificationResult {
    Unknown,                      // 0 — default, treated as failure
    Success,                      // 1
    RootCertNotTrusted,           // 2
    IntermediateCertsNotTrusted,  // 3
    InvalidTimestamp              // 4
}

No call-site changes are needed — all existing checks use the pattern journal.result != VerificationResult.Success, which naturally treats Unknown as a failure.

Testing

• All 72 NitroEnclaveVerifierTest tests pass
• All 31 TEEProverRegistryTest tests pass
• Lint/fmt passes
• Snapshots regenerated with --force

Note

This is an ABI-breaking change for the VerificationResult enum (numeric values shift by +1). Off-chain systems that produce or consume VerificationResult values (e.g., ZK prover programs) will need coordinated updates.

[cb-heimdall]

✅ Heimdall Review Status

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