Raise the mesh as it is in the gate, call a baseline that does not compose an error, and let a check run by hand as the seat runs it

The gate composed 0 of 4 machines with the change and without, and passed every change: the store it
raised held each module's bus credential but no account for it (issue 203's refusal), no outward links
(so no filter could be composed), and refused settings the mesh holds. Now the account is minted with
its credential, the facts carry each machine's outward links (a stand-in for an older snapshot), the
mesh's layers are kept as held, and a withheld path keeps a path's shape. A machine the mesh composes
that the gate cannot raise makes the verdict an error, never a pass; the verdict alone is on stdout.

A merge-check.sh that passed on an agent's machine failed on the build seat: a newer gofmt, siblings at
a feature branch, another user. `mesh-controller check-here` runs builder.Check with the ask the
controller would make, from facts that now name the toolchains and the refs cloned beside; a failed
script is said by what failed. (novox/hq issues 282, 283)

cmd/mesh-controller/main.go

@@ -123,6 +123,9 @@ func run() error {
 	// The merge gate: every machine of the snapshot composed with a change (novox/hq to-be 45 §9).
 	case "merge-gate":
 		return mergeGateCommand(ctx, args[1:])
+	// A pull request's merge check run here exactly as the build seat runs it (novox/hq issue 283).
+	case "check-here":
+		return checkHereCommand(ctx, args[1:])
 	case "upgrade":
 		return upgradeCommand(ctx, args[1:])
 	// The bus as a planned step (novox/hq to-be 45 §8, ADR 0236).