Send a merge's builds to every machine at once, with no first-machine gate (hq ADR 0360)

The operator chose the leanest rollout: no gate, no one machine first, failures loud and fixed forward.
A walk sends every rolled-out module to every machine running it in one step, built-by orders no tier,
and a walk ends on its machines' reports. The backlog walk sends every machine at once and passes each
on its applied report.

cmd/mesh-controller/release_plan_test.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"slices"
 	"testing"
 	"time"
 
@@ -49,8 +50,10 @@ func TestAMergeIsPlannedInTiersAlongTheThreeKindsOfDependency(t *testing.T) {
 	if pos["mesh-tools"] != 0 || pos["builder"] != 1 {
 		t.Fatalf("the runtime then the builder: %v", tiers)
 	}
-	if !(pos["shop"] > pos["builder"] && pos["postgres"] > pos["builder"]) {
-		t.Fatalf("what the builder builds comes after the builder: %v", tiers)
+	// Built-by orders nothing (novox/hq ADR 0360 §3): what the builder builds is beside it, after the runtime it
+	// stands on.
+	if pos["shop"] != 1 || pos["postgres"] != 1 {
+		t.Fatalf("what the builder builds waits for the builder: %v", tiers)
 	}
 	if pos["shop-plugin"] <= pos["shop"] {
 		t.Fatalf("a plugin after what it is declared on: %v", tiers)
@@ -67,24 +70,23 @@ func TestAMergeIsPlannedInTiersAlongTheThreeKindsOfDependency(t *testing.T) {
 	// A change to a package all three build from moves all three. The builder holds
 	// the build seat, whose worker the controller defines, so it follows the controller (worker-of,
 	// novox/hq issue 206), and the controller's built-by edge to it yields: the controller is built by the
-	// build machine that is running. The proxy is built by the new builder: the controller, the builder,
-	// the proxy — the live plan of every controller merge. (This read "the builder, then the controller
-	// and the proxy together" before issue 206, and the fixture had no worker-of edge.)
+	// build machine that is running. The proxy is built by whichever builder runs, so it goes beside the
+	// controller (novox/hq ADR 0360 §3; it read "the controller, the builder, the proxy" before).
 	small := reachableFrom([]string{"mesh-controller", "builder", "route-proxy"}, edges)
 	smallTiers := tiersOf(small, edges)
-	if got := tiered(smallTiers); got != "mesh-controller | builder | route-proxy" {
-		t.Fatalf("the controller, then the builder, then the proxy: %v", smallTiers)
+	if got := tiered(smallTiers); got != "mesh-controller,route-proxy | builder" {
+		t.Fatalf("the controller and the proxy, then the builder: %v", smallTiers)
 	}
 	// The builder alone moved: the builder, and nothing it builds.
 	if only := reachableFrom([]string{"builder"}, edges); len(only) != 1 {
 		t.Fatalf("a build machine change rebuilds the build machine alone: %v", only)
 	}
 
-	// Only a runtime dependency gates on deployment, and only when the module rolls out.
+	// Nothing waits on deployment for a built-by edge (novox/hq ADR 0360 §3): the builder gates no tier after it.
 	p := planOfMerge(link.SourceMoved{Owner: "novox", Repo: "mesh-tools", Commit: "abc"}, []string{"mesh-tools"}, edges)
 	p.Tier = pos["builder"]
 	rollsOut := func(m string) bool { return m == "builder" }
-	if g := gates(p, edges, rollsOut); len(g) != 1 || g[0] != "builder" {
+	if g := gates(p, edges, rollsOut); len(g) != 0 {
 		t.Fatalf("the builder gates the tier after it: %v", g)
 	}
 	p.Tier = 0
@@ -253,10 +255,10 @@ func TestAChangeToTheBuildAgentRebuildsTheBuildAgentAlone(t *testing.T) {
 			t.Fatalf("%v planned %v: the build agent alone", paths, p.Tiers)
 		}
 	}
-	// With what it builds moved beside it, the agent comes first and they follow: an order, not a widening.
+	// With what it builds moved beside it, both go in one tier (novox/hq ADR 0360 §3): built-by orders nothing.
 	p := planOfMerge(link.SourceMoved{Owner: "novox", Repo: "mesh-catalog", Commit: "abc"},
 		[]string{"build-agent", "redis"}, edges)
-	if len(p.Tiers) != 2 || p.Tiers[0][0] != "build-agent" || p.Tiers[1][0] != "redis" || len(p.Modules) != 2 {
-		t.Fatalf("the agent, then what moved beside it: %v", p.Tiers)
+	if len(p.Tiers) != 1 || !slices.Equal(p.Tiers[0], []string{"build-agent", "redis"}) || len(p.Modules) != 2 {
+		t.Fatalf("the agent and what moved beside it, in one tier: %v", p.Tiers)
 	}
 }