BACKLOG: J4 done, tried on the PoC with the first mirror stopped

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

BACKLOG.md

@@ -30,16 +30,11 @@ What is left, most needed first. The detail is in the item each names.
 **Soon: the customer's experience, and HA.**
 4. ~~**C24**~~: done 2026-10-21. The store's, catalog's and mirror's errors, percent signs, footer times and stale
    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. 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.
+5. ~~**J4**~~: done 2026-10-29. The done-criterion held on the PoC: with mirror 146 stopped, `ctl model serve` of a
+   new model was fetched by the second mirror (VM 167, 10.0.0.152), placed and answered; a node without a file
+   146's address names was given 152's; what was added meanwhile reached 146 when it came back; a removal was
+   carried both ways. Found and fixed there: add-peer on a mirror machine of its own, files without checksums never
+   copied, and `mirror remove` neither recorded nor seen by the running mirror.
 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
@@ -1652,7 +1647,7 @@ their own (4 cores, 32 GB, two cores each) the same test refused 2.
 - Done when: the setup installs the judges on the machines given for them,
   and the load test above refuses no more than it did by hand.
 
-### J4. The model mirror on more than one machine (M)
+### J4. The model mirror on more than one machine (M) — done 2026-10-29, tried on the PoC
 In an HA install the mirror stays on the first machine. While it is down,
 models the nodes already have keep serving and new ones wait for it.
 - A second mirror kept in step (each machine of the store, or one more), the