BACKLOG: J4 tried on two machines

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

BACKLOG.md

@@ -32,8 +32,14 @@ What is left, most needed first. The detail is in the item each names.
    forms are in the page's language. Left: the /docs documents, and a language kept per person (cookie only today).
 5. **J4**: the model mirror on more than one machine. Code done 2026-10-29: mirrors kept in step (`mirror serve
    --peer`, removals carried), `mirror.peers` and failover in the control plane, nodes given the file on a mirror that
-   answers, `mirror add-peer` and the setup's second mirror. Left: the "done when" on machines, the first mirror off
-   while a model is added and served.
+   answers, `mirror add-peer` and the setup's second mirror. Tried 2026-10-29 on two VMs:
+   - `add-peer` set the second up over ssh;
+   - a file came across in ~30 s, checksum matching;
+   - a version added on the second while the first was off reached the first when it came back;
+   - one removed on the first while the second was off was removed there when it came back, not copied back.
+
+   Left: the same with a control plane and a node, a model served while the first mirror is off. That part (failover
+   in the control plane, the node given the other mirror's file) is so far tried only in tests.
 6. **F5**: large imports limited by the embedding engine's slots. (M)
 
 **From Kong** (section L): L1–L5 and L9 done (v0.15.0); left of L4 is routing by cost between outside