Refine substrate-mutation gate (learn/agentos carve-out + reviewer enforcement)

Context

Follow-up to PR #10792 (V2 of Epic #10757 - mutation-time substrate gate). @neo-opus-4-7 approved #10792 but identified two polish concerns during Cycle 1 review that are better tracked as follow-ups rather than churning the current PR.

This ticket captures those refinements, using PR #10792 and the cycle-2 V2 substrate as the empirical anchor. It ensures the mutation-time substrate gate is enforced symmetrically without capturing false positives in operator guides.

The Problem

1. Scope Ambiguity (learn/agentos/**): The current mutation-time gate detection scope does not distinguish between agent-loaded substrate (which needs the strict net-reduce/mitigation rationale) and External Operator Guides. Operator guides already carry their own in-doc slot-rationale via the Compaction Taxonomy block. Subjecting them to the PR-body slot-rationale is redundant and creates friction.
2. Asymmetric Enforcement Risk: The reviewer-side enforcement shape is ambiguous. There is no Required Action template language in pr-review-template.md (or the pr-review skill) for a missing slot-rationale in the PR body. This creates an asymmetric enforcement risk where authors are instructed to do it, but reviewers lack a structured hook to enforce it, violating the feedback_skill_adherence_asymmetry lesson.

The Architectural Reality

• .agents/skills/pull-request/references/pull-request-workflow.md — Defines the Pre-Flight gate triggering on AGENTS.md, AGENTS_ATLAS.md, .agents/skills/**, and learn/agentos/**.
• .agents/skills/pr-review/references/pr-review-template.md — The template used by reviewers to evaluate PRs, currently lacking explicit checkpoints for the substrate-mutation gate.
• learn/agentos/** — Mixed-purpose directory containing both active agent context and operator reference docs.

The Fix

1. Scope Carve-out: Introduce a carve-out OR in-doc-equivalence rule for learn/agentos/** in pull-request-workflow.md. If a document already carries an in-doc slot-rationale (like operator guides), the PR-body requirement is waived.
2. Reviewer Enforcement: Update pr-review-template.md (and/or pr-review skill) to include explicit Required Action template language for missing PR-body slot-rationales. This ensures symmetrical enforcement by both author and reviewer.

Acceptance Criteria

• (AC1) Update pull-request-workflow.md to explicitly carve out or establish an in-doc-equivalence rule for learn/agentos/** files that already contain Compaction Taxonomy blocks.
• (AC2) Update pr-review-template.md (or related review skill files) to add explicit Required Action language for enforcing the substrate-mutation gate when a PR body lacks the required slot-rationale.
• (AC3) Ensure the new language clearly distinguishes agent-loaded substrate from operator-facing documentation.

Out of Scope

• Retroactive review of previously merged PRs.
• Mechanical hook/lint implementation for enforcement (remains discipline-only for now).

Avoided Traps

• Churning PR #10792: Keeping these refinements as a follow-up ticket prevents stalling the baseline value delivered by PR #10792.
• Asymmetric Enforcement: Adding the rule to the author side without the reviewer side ensures the gate doesn't decay from neglect.

Related

• Parent Epic: #10757
• Empirical Anchor: PR #10792 (and review comment IC_kwDODSospM8AAAABBUS4xw)
• Sibling Ticket: #10765

Origin Session ID: 16d941df-38f0-41f4-92e7-bd82aed48dfa

Retrieval Hint: query_raw_memories(query="substrate-mutation gate refinements learn/agentos carve-out asymmetric enforcement PR 10792")