EPIC: T27-first CI enforcement, exception registry, and migration scoreboard #1664

Goal

Prevent avoidable new foreign-language implementation from entering Trinity and make migration progress measurable using evidence-backed CI gates.

Boundary

This epic implements policy enforcement and reporting, not the full port of legacy code. Do not fail builds on vendor-required/generated files or approved narrow exceptions without classification. Implement the scanner in T27 when the necessary filesystem/Git capabilities are available.

User Scenarios & Testing

• A pull request adding avoidable Python/JS/TS/shell behavior receives an actionable CI failure.
• An approved external adapter remains allowed only within its documented scope and expiry/removal condition.
• Maintainers can see remaining migration work by repository, language, risk, and workstream.

Requirements

• Derive rules from the canonical T27-native policy and inventory classifications.
• Scan changed files and relevant executable metadata; distinguish implementation from fixtures, generated files, and declarative configuration.
• Maintain an exception registry with rationale, owner, affected paths, approval evidence, expiry or removal condition.
• Report violations with file paths and remediation instructions.
• Track inventory coverage, T27-native share, risk-weighted migration progress, and unresolved classifications.
• Add tests for false positives, false negatives, exception expiry, and changed-file behavior.
• Keep any bootstrap-language exception explicit and tracked as migration debt.

Success Criteria

• CI blocks a tested set of avoidable foreign-language additions and gives actionable output.
• Approved exceptions are narrow, auditable, and have a removal condition or expiry.
• Generated/vendor/config/fixture cases are covered by tests.
• Scoreboard metrics are reproducible from repository evidence.
• No migration percentage is reported without defined denominator and measured coverage.
• Enforcement itself is tested and does not silently bypass the policy.