ARM API Reviewer agent: formalize Reviewer / Critic wire protocol as a shared, versioned contract #43646

Background

The ARM API Reviewer agent now invokes an ARM API Review Critic sub-agent (#43302, implemented in PR #43494) to independently re-validate every finding before it is presented to a human for posting. The two agents exchange a structured set of inputs, verdicts, and telemetry markers on every iteration. Without a single source of truth for that exchange, each agent file drifts independently: input field names diverge, marker schemas disagree, override semantics fall out of sync, and the gate silently degrades.

Proposal

Maintain the Reviewer / Critic contract in a dedicated .github/agents/protocols/ directory, separate from either agent file. The protocol defines:

• The ten Critic inputs the Reviewer must pass on every dispatch (PR URL, session SHA, full Step 6 report, file list, previous-version base source, Step 5.5 reconciliation plan, prior FAIL-set summary, considered-and-declined list, graph-production flag, iteration number) plus a verbatim YAML template (# critic-inputs/v1) the Reviewer pastes into every dispatch.
• The four Critic verdict tracks (Finding accuracy, Graph integrity, Reconciliation accuracy, Coverage quality) and the authorization rule that gates posting.
• The <!-- review-state: ... --> per-response marker (response-scope: critic-mode, iteration, PR identity).
• The 6-field per-comment telemetry marker (finding-scope: rule, severity, classification, critic, head-sha, plus optional downstream-rule, override-reason, and the telemetry: degraded fallback form).
• The Override-reason validator (length + boilerplate denylist + structured-anchor or verbatim-quote requirement) applied identically by both agents.
• The non-overridable FAIL catalog (reconciliation FAILs, graph fabrication, downstream-ci-conflict, suppression-path-mismatch, unescaped-mention, override-reason-invalid).

References

• .github/agents/protocols/reviewer-critic.protocol.md: canonical contract introduced by PR Add ARM API Review Critic agent #43494.
• .github/agents/protocols/critic-inputs.template.md: Critic-input YAML template.
• Umbrella issue: #43302.

Acceptance criteria

• The protocol file is the single source of truth; both agent files reference it and do not duplicate field semantics.
• Either agent's restatement of a protocol field is byte-faithful or is flagged as a bug.
• A new contributor can change one of the markers in exactly one place and have both agents pick it up consistently.