fix(lbug): lock queryImporters against the WAL driver (#2264)

queryImporters issued a raw conn.query on the singleton connection inside the
importer-BFS loop of incremental --pdg writeback, while the WAL-checkpoint driver
could fire a concurrent CHECKPOINT — the same double-free class. Wrap the read
(query + getAll + drain) in withConnLock.

Extends lbug-conn-serialization.test.ts with a routing assertion.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JBJomjoTdBV2eveDVq4JMm

gitnexus/src/core/lbug/lbug-adapter.ts

@@ -2003,7 +2003,8 @@ export const getEmbeddingTableName = (): string => EMBEDDING_TABLE_NAME;
  * exports.
  */
 export const queryImporters = async (targetFilePath: string): Promise<string[]> => {
-  if (!conn) {
+  const c = conn;
+  if (!c) {
     throw new Error('LadybugDB not initialized. Call initLbug first.');
   }
   const escaped = targetFilePath.replace(/'/g, "''");
@@ -2012,22 +2013,27 @@ export const queryImporters = async (targetFilePath: string): Promise<string[]>
     WHERE r.type = 'IMPORTS' AND b.filePath = '${escaped}'
     RETURN DISTINCT a.filePath AS importer
   `;
-  let queryResult: lbug.QueryResult | lbug.QueryResult[] | undefined;
-  try {
-    queryResult = await conn.query(cypher);
-    const result = Array.isArray(queryResult) ? queryResult[0] : queryResult;
-    const rows = await result.getAll();
-    const out: string[] = [];
-    for (const row of rows) {
-      const v = (row as { importer?: unknown }).importer;
-      if (typeof v === 'string' && v.length > 0) out.push(v);
+  // Runs inside the connection lock: queryImporters is called in the importer-BFS
+  // loop during incremental --pdg writeback while the WAL driver is live, so an
+  // unlocked conn.query here could race a concurrent CHECKPOINT on the singleton.
+  return withConnLock(async () => {
+    let queryResult: lbug.QueryResult | lbug.QueryResult[] | undefined;
+    try {
+      queryResult = await c.query(cypher);
+      const result = Array.isArray(queryResult) ? queryResult[0] : queryResult;
+      const rows = await result.getAll();
+      const out: string[] = [];
+      for (const row of rows) {
+        const v = (row as { importer?: unknown }).importer;
+        if (typeof v === 'string' && v.length > 0) out.push(v);
+      }
+      return out;
+    } catch {
+      return [];
+    } finally {
+      if (queryResult) await closeQueryResults(queryResult);
     }
-    return out;
-  } catch {
-    return [];
-  } finally {
-    if (queryResult) await closeQueryResults(queryResult);
-  }
+  });
 };
 
 /**

gitnexus/test/integration/lbug-conn-serialization.test.ts

@@ -41,5 +41,12 @@ withTestLbugDB('conn-serialization', () => {
       expect(lockSpy).toHaveBeenCalled();
       expect(result).toMatchObject({ nodesDeleted: 0 });
     });
+
+    it('U2: queryImporters routes through withConnLock', async () => {
+      const { queryImporters } = await import('../../src/core/lbug/lbug-adapter.js');
+      const importers = await queryImporters('any/path.ts');
+      expect(lockSpy).toHaveBeenCalled();
+      expect(importers).toEqual([]);
+    });
   });
 });