[Quality] Create an immutable verifier decision audit trail

[1nonlypiece]

Problem

Review outcomes need a durable history that explains who made a decision, what evidence was used, and when the decision changed.

This issue requires a meaningful production implementation. Typo-only, documentation-only, formatting-only, dependency-only, or cosmetic changes do not satisfy the scope.

Objective

Persist append-only audit records for validation assignment, approval, rejection, and reassignment events.

Scope

Define the audit schema, actor identity, previous and next state, reason metadata, retention, and read authorization.

Acceptance criteria

• Every state transition emits exactly one audit record.
• Audit records cannot be edited through application APIs.
• Readers cannot access records outside their permitted scope.
• Tests verify ordering, actor attribution, redaction, and duplicate-event handling.
• Existing CI/CD checks remain green.
• The PR explains the design, tradeoffs, test evidence, and any remaining limitations.
• The PR references this issue with Closes #{issue-number} or Fixes #{issue-number}.

Implementation notes

Implement only the stated behavior; keep unrelated refactors out of the PR.

Non-goals

• Do not remove tests merely to make CI pass.
• Do not introduce secrets, private keys, credentials, or mainnet-only values.
• Do not change unrelated APIs, UI surfaces, contract behavior, or deployment configuration.

Contributor application

Before starting, comment with relevant experience, a 1–4 bullet implementation approach, and an estimate for opening the first draft PR. Wait for maintainer assignment before coding. Only the assigned contributor is eligible for reward consideration.

Submission requirements

• Use PR title format [#<issue-number>] <short summary>.
• Check off each completed acceptance criterion.
• Include focused automated tests for success, failure, authorization, and boundary behavior where applicable.
• Include the validation commands and results in the PR description.
• Address maintainer review feedback before merge.

GrantFox reward consideration is based on the original scope, implementation quality, tests, security review, CI/CD results, review feedback, and follow-up stability; completion or merge alone is not a guarantee.

[guptakumarranjeet150]

Hello @maintainers,

I would like to resolve this issue. Here is my proposed execution plan:

• Implementation: Structure backend handlers for [Quality] Create an immutable verifier decision audit trail with strict input validation, proper HTTP error codes, and idempotent execution.
• Testing & Verification: Cover implementation with end-to-end integration tests for standard and edge-case inputs.
• Delivery: Ready to ship a thoroughly tested PR within 12–24 hours with passing CI.

I am ready to start immediately—please assign this to me!