[GrantFox][High] Make circuit-breaker transitions explicit

Summary

Make circuit-breaker transitions explicit

Why this matters

Circuit-breaker state must prevent unsafe operations while allowing authorized recovery.

Scope

Define closed, open, and half-open transitions, triggers, cooldown, and event output.

Acceptance criteria

• Unsafe operations are blocked while open.
• Only authorized recovery can close or probe the circuit.
• Cooldown boundaries are deterministic.
• Tests cover repeated failures, recovery, and unauthorized calls.

Validation

Add regression coverage for existing behavior, failure modes, authorization boundaries, and compatibility. The implementation must pass the repository CI checks.

Non-goals

• Typo-only, formatting-only, or documentation-only changes.
• Unrelated refactors or dependency upgrades.
• Weakening existing security, authorization, CI, or production safeguards.

Contributor application

Before implementation, comment with relevant experience, a 1–4 bullet approach, and an estimate for opening the first draft PR. Wait for maintainer assignment before coding.

PR requirements

Use a feature branch, include Closes #<issue-number>, check every acceptance criterion, link criteria to code/tests, explain security and failure-mode considerations, and pass CI.

Reward-readiness

This is a substantive GrantFox campaign issue. Merge and CI success do not by themselves guarantee reward eligibility; final reward-readiness is determined by campaign review.

Start by locating the existing circuit-breaker implementation and its current regression coverage in the repository, then review the repository CI checks. Done means explicit closed, open, and half-open behavior with deterministic cooldowns, authorization boundaries, event output, and tests for blocked operations, repeated failures, recovery, and unauthorized calls.