feat: use random subject frame extraction

.memory/worklog.json

@@ -1,12 +1,5 @@
 {
   "entries": [
-    {
-      "files_changed": 1,
-      "hash": "eeeaebd",
-      "message": "auto-save 2026-05-15 17:50 (~1)",
-      "ts": "2026-05-15T17:50:32+08:00",
-      "type": "commit"
-    },
     {
       "files_changed": 3,
       "message": "Codex 会话活跃 · 最近命令：codex · 3 项未提交变更 · 最近提交：auto-save 2026-05-15 17:50 (~1)",
@@ -3257,6 +3250,13 @@
       "message": "auto-save 2026-05-18 15:07 (~5)",
       "hash": "ebac2e8",
       "files_changed": 5
+    },
+    {
+      "ts": "2026-05-18T15:13:30+08:00",
+      "type": "commit",
+      "message": "auto-save 2026-05-18 15:13 (~8)",
+      "hash": "2a1aa4c",
+      "files_changed": 8
     }
   ]
 }