docs(engine): document the deliberate gate-advisory twin divergence (#5784)

Record the keep-divergent decision for the gate-decision advisory twins (#4881):
src/rules/advisory.ts (host) and packages/loopover-engine/src/advisory/gate-advisory.ts
(engine). Add header docs to both explaining that they are intentionally NOT
converged — the host copy reaches into the full signals subsystem (isCodeFile,
isTestPath, scoring/preview, signals/engine types) while the engine copy is a
slimmed re-implementation, precisely so @loopover/engine and its CLI consumers
never pull the ~5,800-line signals/engine into their dependency graph. Note that
scripts/check-engine-parity.ts keeps the core gate-decision functions in
lock-step, and that converging must wait until the dependency-graph constraint is
solved. Comments only — no gate-decision behavior changes.

Closes #4881

Author: real-venus

packages/loopover-engine/src/advisory/gate-advisory.ts

@@ -1,3 +1,11 @@
+// Gate-decision advisory logic — ENGINE copy. This is an intentionally-divergent twin of the host
+// src/rules/advisory.ts (#4518; keep-divergent decision recorded for #4881). This slimmed re-implementation uses
+// predicted-gate-types + ../scoring/label-match and deliberately imports none of ../signals/engine, isCodeFile, or
+// isTestPath, so @loopover/engine — and the CLI packages that consume it (packages/loopover-miner,
+// packages/loopover-mcp) — never pull the ~5,800-line signals/engine subsystem into their dependency graph. The
+// core gate-decision functions are kept structurally in lock-step with the host copy by
+// scripts/check-engine-parity.ts (GATE_DECISION_CORE_MARKERS); do NOT converge to a single source until that
+// dependency-graph constraint is solved — see #4881.
 import { randomUUID } from "node:crypto";
 import type {
   Advisory,

src/rules/advisory.ts

@@ -1,3 +1,21 @@
+// Gate-decision advisory logic — HOST copy. This is an intentionally-divergent twin of the engine's
+// packages/loopover-engine/src/advisory/gate-advisory.ts (#4518; keep-divergent decision recorded for #4881). The
+// two are deliberately NOT converged to a single source.
+//
+// Why kept divergent: this host copy reaches into the full signals subsystem — `isCodeFile`
+// (../signals/local-branch, which transitively pulls the whole review-scoring / GitHub-API graph), `isTestPath`
+// (../signals/test-evidence), `labelMatchesPattern` (../scoring/preview), and the CollisionCluster/CollisionReport
+// types from the ~5,800-line ../signals/engine. The engine twin is a slimmed re-implementation (slim
+// predicted-gate-types + ../scoring/label-match, importing none of signals/engine) precisely so @loopover/engine —
+// and the CLI packages that depend on it (packages/loopover-miner, packages/loopover-mcp) — never drag
+// signals/engine and its subsystem into their dependency graph.
+//
+// What keeps this safe: scripts/check-engine-parity.ts (GATE_DECISION_CORE_MARKERS) asserts BOTH files still export
+// the core gate-decision functions (evaluateGateCheck / evaluateGateCheckCore / isConfiguredGateBlocker /
+// buildPullRequestAdvisory), so the gate *decision* stays in lock-step even though the surrounding types and
+// imports diverge. Do NOT converge these into a single shim until the dependency-graph-size constraint is solved
+// (e.g. a shared type-only module carrying CollisionReport without dragging the signals implementation along) — see
+// #4881.
 import type {
   Advisory,
   AdvisoryConclusion,