refactor(lbug): keep relation pair parsing in router

gitnexus/src/core/lbug/csv-generator.ts

@@ -17,12 +17,14 @@ import { createWriteStream, WriteStream } from 'fs';
 import path from 'path';
 import type { GraphNode, GraphRelationship } from 'gitnexus-shared';
 import { KnowledgeGraph } from '../graph/types.js';
-import { NodeTableName, NODE_TABLES, RELATION_SCHEMA_PAIRS } from './schema.js';
-import { RelPairRouter } from './rel-pair-routing.js';
+import { NodeTableName, NODE_TABLES, RELATION_SCHEMA } from './schema.js';
+import { parseRelationSchemaPairs, RelPairRouter } from './rel-pair-routing.js';
 import { parseTruthyEnv } from '../ingestion/utils/env.js';
 import { SYMBOL_NODE_LABELS } from '../ingestion/utils/symbol-labels.js';
 import { applyCjkSegmentationIfEnabled } from '../search/cjk-segmentation.js';
 
+const DECLARED_RELATION_PAIRS = parseRelationSchemaPairs(RELATION_SCHEMA);
+
 /**
  * Deterministic output ordering — optional (out-of-core / windowed-resolve
  * enabler). When `GITNEXUS_SORT_GRAPH_OUTPUT` is set, nodes and relationships
@@ -789,7 +791,7 @@ export const streamAllCSVsToDisk = async (
       csvDir,
       REL_CSV_HEADER,
       new Set<string>(NODE_TABLES),
-      RELATION_SCHEMA_PAIRS,
+      DECLARED_RELATION_PAIRS,
     );
     try {
       let emitted = 0;

gitnexus/src/core/lbug/rel-pair-routing.ts

@@ -48,6 +48,22 @@ export const getNodeLabel = (nodeId: string): string => {
   return nodeId.split(':')[0];
 };
 
+/**
+ * Extract the FROM→TO pairs accepted by a relationship DDL.
+ *
+ * This belongs at the routing boundary: schema.ts owns the DDL, while the CSV
+ * router owns the fail-fast check that prevents writing a pair LadybugDB cannot
+ * COPY. Backticks quote schema labels and are not part of the graph label.
+ */
+export const parseRelationSchemaPairs = (relationSchema: string): ReadonlySet<string> =>
+  new Set(
+    [
+      ...relationSchema.matchAll(
+        /\bFROM\s+`?([A-Za-z][A-Za-z0-9_]*)`?\s+TO\s+`?([A-Za-z][A-Za-z0-9_]*)`?/g,
+      ),
+    ].map((match) => `${match[1]}|${match[2]}`),
+  );
+
 export interface RelPairMeta {
   csvPath: string;
   rows: number;

gitnexus/src/core/lbug/schema.ts

@@ -462,21 +462,6 @@ CREATE REL TABLE ${REL_TABLE_NAME} (
   step INT32
 )`;
 
-/**
- * Declared FROM→TO label pairs for the single relationship table.
- *
- * Derived from the DDL itself so the CSV router and LadybugDB schema cannot
- * drift into separate allowlists. Backticks are schema quoting, not part of a
- * node label.
- */
-export const RELATION_SCHEMA_PAIRS: ReadonlySet<string> = new Set(
-  [
-    ...RELATION_SCHEMA.matchAll(
-      /\bFROM\s+`?([A-Za-z][A-Za-z0-9_]*)`?\s+TO\s+`?([A-Za-z][A-Za-z0-9_]*)`?/g,
-    ),
-  ].map((match) => `${match[1]}|${match[2]}`),
-);
-
 // ============================================================================
 // EMBEDDING TABLE SCHEMA
 // Separate table for vector storage to avoid copy-on-write overhead

gitnexus/test/unit/rel-pair-routing.test.ts

@@ -3,7 +3,11 @@ import { EventEmitter } from 'events';
 import fs from 'fs';
 import path from 'path';
 import os from 'os';
-import { RelPairRouter, getNodeLabel } from '../../src/core/lbug/rel-pair-routing.js';
+import {
+  RelPairRouter,
+  getNodeLabel,
+  parseRelationSchemaPairs,
+} from '../../src/core/lbug/rel-pair-routing.js';
 
 /**
  * Unit tests for RelPairRouter (#2203 U2) — the production per-pair emit path.
@@ -98,6 +102,20 @@ describe('getNodeLabel', () => {
   });
 });
 
+describe('parseRelationSchemaPairs', () => {
+  it('extracts plain and quoted FROM→TO labels for router validation', () => {
+    expect(
+      parseRelationSchemaPairs(`
+        CREATE REL TABLE CodeRelation(
+          FROM Class TO CodeElement,
+          FROM \`Enum\` TO \`TypeAlias\`,
+          type STRING
+        )
+      `),
+    ).toEqual(new Set(['Class|CodeElement', 'Enum|TypeAlias']));
+  });
+});
+
 describe('RelPairRouter', () => {
   it('routes valid edges to per-pair files (header first) and skips invalid-label edges', async () => {
     const streams: MockWriteStream[] = [];

gitnexus/test/unit/schema.test.ts

@@ -19,7 +19,6 @@ import {
   PROCESS_SCHEMA,
   BASICBLOCK_SCHEMA,
   RELATION_SCHEMA,
-  RELATION_SCHEMA_PAIRS,
   EMBEDDING_SCHEMA,
   CREATE_VECTOR_INDEX_QUERY,
 } from '../../src/core/lbug/schema.js';
@@ -211,7 +210,6 @@ describe('LadybugDB Schema', () => {
 
     it('persists consumer Class injection edges to synthetic provider declarations', () => {
       expect(RELATION_SCHEMA).toContain('FROM Class TO CodeElement');
-      expect(RELATION_SCHEMA_PAIRS.has('Class|CodeElement')).toBe(true);
     });
 
     it('has all FROM/TO pairs needed for HAS_METHOD edges', () => {