Judge every pull request against the mesh that runs, before it merges (hq ADR 0237, to-be 45 §9)

Every check the mesh had ran after a merge, on a machine: a manifest the node-engine refused
(236), an identity a real machine's name made too long (263). merge-gate raises the mesh as the
facts snapshot says it is and the mesh with the change, each in a throwaway store through the
controller's own records, composes every machine twice and validates it with the node-engine's
validator, and fails what the change breaks, naming the machine's roles and the module - plus a
manifest the judging controller cannot read, a consumer left out of its grant, a module removed
while a machine runs it, a new module the node-engine would refuse; it warns on a wide rebuild.

The forge's new head of a pull request becomes a check the controller asks of the build seat:
the head and, beside it, the controller the mesh runs, the catalogue, the host and the lab; a
throwaway store and bus of the versions the mesh runs; the repository's merge-check.sh in the
mesh's Go toolchain with no container runtime socket; then mesh-lab's replays. The verdict is
said as checked, an error never a pass, and nothing is recorded or registered.

cmd/mesh-controller/main.go

@@ -117,6 +117,9 @@ func run() error {
 	// The facts snapshot a merge check is fed (novox/hq to-be 45 §9).
 	case "facts":
 		return factsCommand(ctx, args[1:])
+	// 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:])
 	case "upgrade":
 		return upgradeCommand(ctx, args[1:])
 	// The bus as a planned step (novox/hq to-be 45 §8, ADR 0236).
@@ -335,6 +338,12 @@ func parseAround(set *flag.FlagSet, args []string) ([]string, error) {
 // registered, the same as the waiting command does. Said either way, so the daemon's log tells what
 // became of a build nobody was watching.
 func (b builds) Built(ctx context.Context, result link.BuildResult) error {
+	// **A merge check builds nothing** (novox/hq to-be 45 §9): its verdict is said, and nothing of it is
+	// recorded or registered.
+	if result.Check != nil || result.Checked != nil {
+		checked(ctx, result)
+		return nil
+	}
 	// **A dry run is looked at, never taken in** (novox/hq issue 240). On 2026-10-04 a dry run of an
 	// unmerged branch was heard here like any build, registered, and its definition reached a machine
 	// before anyone had reviewed it.