fix: drop stale hardcoded sidechat UUID, use job-sidechats.json mapping

- bin/dm.py: remove 646 tasks -> 1e75a740 from SIDCHAT_ALIASES. That UUID is stale (not a valid thread on 646 account; SPA redirects elsewhere, causing misdelivery). Alias now falls through to job-sidechats.json/autoprovision. Do NOT re-add hardcoded UUIDs.

- job-sidechats.json: live autoprovisioned mappings for 646-pip and 646 tasks (2026-10-04).

- bin/box-chat-cdp.py: CDP robustness -- drain events until command response, retry switcher lookup while SPA settles, fresh reconnect per retry (transient NO_SWITCHER on pip/opm 2026-10-04).

Session: sidechat/uuid-stale-fix

job-sidechats.json

@@ -47,5 +47,15 @@
     "thread_uuid": "fbc37533-3908-460e-bb82-58a7edbe5f30",
     "agent": "opm",
     "created_at": "2026-10-04T17:17:48.449687+00:00"
+  },
+  "646-pip": {
+    "thread_uuid": "75feb3a2-be36-499a-b314-bfd5803f1db0",
+    "agent": "pip",
+    "created_at": "2026-10-04T18:01:17.397213+00:00"
+  },
+  "646 tasks": {
+    "thread_uuid": "1dfb3199-2f99-446c-83e3-848ae2da0a12",
+    "agent": "646",
+    "created_at": "2026-10-04T18:30:21.863666+00:00"
   }
 }