docs(method): time the disc mesh suite -- 22 minutes of silence is not a hang

Two runs were killed this session for looking stuck. Measured: 1 318 s serial,
no output while it runs. Also records that `build-reborn test` forces
--workspace and silently ignores a `-p`, so scoping needs the cargo
passthrough (`build-reborn t -p <crate>`).

docs/re/METHOD.md

@@ -874,3 +874,9 @@ agent's loop prompt, i.e. nowhere durable. See [`README.md`](README.md) for the
   a flake, and it reproduces when run alone. `-- --test-threads=1` passes 8/8 in
   20 s. Before believing a SIGKILL in this repo, re-run the suite serially;
   before believing a *pass*, check nothing else heavy was sharing the box.
+  ⚠️ And budget for `mesh_consistency_disc`: it takes **22 minutes** (1 318 s
+  measured, serial) and produces no output while it runs, so `build-reborn test`
+  looks hung for a third of an hour. It is not. Two runs were killed for looking
+  stuck before it was timed. If the change under test is not in the mesh path,
+  `build-reborn t -p <crate>` scopes around it — note that `build-reborn test`
+  itself passes `--workspace` and will ignore a `-p`.