docs: add review escalation rule

docs/REVIEW-ESCALATION-RULE.md

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+# Review Escalation Rule
+
+Open Problem Lab should make it clear when ordinary review is not enough.
+
+This guide defines simple triggers for escalating a contribution to stronger review before merge or before treating it as repository knowledge.
+
+## Escalation triggers
+
+Escalate review when a contribution:
+
+- changes an accepted artifact's status or boundary;
+- adds a quantitative result used for prioritization;
+- changes a generated index or schema-adjacent artifact;
+- depends on field assumptions;
+- introduces a disputed source;
+- changes a review gate, workflow, or governance rule;
+- affects a claim where being wrong would waste time, money, reviewer trust, or field capacity.
+
+## Escalation note
+
+```markdown
+## Review escalation
+
+**Artifact:** Link to PR, issue, evidence record, or problem-pack section.
+
+**Trigger:** Which escalation trigger applies?
+
+**Needed review:** evidence | domain | quantitative | field | maintainer | replication.
+
+**Risk if skipped:** One sentence.
+
+**Can merge before escalation?** yes | no | only as exploratory.
+```
+
+## Reviewer guidance
+
+A reviewer can approve structure while still escalating substance. The PR should not treat partial review as full acceptance.
+
+## Agent guidance
+
+Agents should propose escalation when their work changes status, metrics, review gates, or field-facing claims.
+
+## Acceptance test
+
+The rule works when a contributor can tell whether a PR needs ordinary review, stronger review, or exploratory-only merge.