trace: check if DBPools blocks in background task

wwwroot/knowledge_bases_list/upload_file.dspy

@@ -29,12 +29,12 @@ ext_l = ext.lower()
 # creates its own DBPools connection. All args are primitives.
 # ============================================================
 async def ingest_doc(doc_id, kb_id, file_name, ext_l, real_path):
-    # DEBUG: verify background_reco executes
-    try:
-        with open('/tmp/_bg_trace_' + doc_id + '.txt', 'w') as df:
-            df.write('ingest_doc started\n')
-    except: pass
     db = DBPools()
+    # TRACE
+    try:
+        with open('/tmp/_t2_' + doc_id, 'w') as df:
+            df.write('db ok, reading file: ' + real_path)
+    except: pass
     text = ''
     chunks_n = 0
     face_count = 0