Say how a check's clones are chosen and what the captured copy carries (issue 432 review)

internal/beside/beside.go

@@ -8,7 +8,12 @@
 //   - In a merge check, the build seat clones each core repository beside the one checked (the catalogue
 //     at its main, the node-engine at the commit the mesh runs) and says where in MESH_CHECK_BESIDE. A
 //     test judges against those clones, so agreement with the other repository is checked where
-//     `mesh/repo-check` runs; a repository missing there fails the test, never skips it.
+//     `mesh/repo-check` runs; a repository missing there fails the test, never skips it. Which clones a
+//     check gets is chosen from the inventory: mesh-catalog by the source of the `nats` module, mesh-host
+//     by the source of `mesh-host`. In a mesh where either module has no source repository nothing is
+//     cloned, and these tests fail loudly with "not beside this check": a cause in the setup, not in the
+//     change. And in a delivery group that holds a mesh-catalog pull request, these tests read the
+//     catalogue's main, not the group's head.
 //   - Anywhere else, the test judges against the copy captured in this repository's testdata/beside, at the
 //     commit testdata/beside/CAPTURED names. Never against a developer's own checkout: to judge one, set
 //     MESH_CHECK_BESIDE to the directory holding it, as the check does.

testdata/beside/CAPTURED

@@ -3,6 +3,10 @@ novox/hq issue 432). Copied from the repositories at the commits below, never wr
 module.json is kept as module.json.captured: a module.json in this repository is a module of it to the
 forge and the planner, and a merge would build and register it.
 
+The copy carries the catalogue's private details: domains, first names in module names, a node name and
+private addresses. That is acceptable while mesh-controller is private; if it ever goes public, this copy is
+a second place to clean besides the catalogue itself.
+
 mesh-catalog  b9de001833b1b61b297182b8e3bcdae1cbdeace9  modules/*/module.json, modules/nats/Dockerfile
 mesh-host     bd5cc6980419c1bd4824be6d58dfebd2381a9de3  examples/foundation-first-node-nats.lock