Give the build modules' steps state an age of two days, and keep a node's pause in a pauses state of its own

mesh-build-go's steps bucket filled to the bus's 64 MiB cap (27,370 keys, none ever removed) and
refused the end of a passed check, so the check read failed; mesh-build-node's (17.8 MB) and
mesh-build-image's grow the same way. A step's key is per step: its reader reads its end within
the step's bound, and a check's verdict is kept by the checker, so two days is ample. The node's
pause key lived in the same bucket and would have ended by itself; it moves to a pauses state
without an age (mesh-sdk fix/steps-bucket-ages, Puller.PausePut). No node is paused today, so
nothing is carried over.

modules/mesh-build-node/cmd/mesh-build-node/asks.go

@@ -54,10 +54,10 @@ func (m *Module) Puller(steps []StepTool, source buildstep.AskSource) *buildstep
 	}
 	ask := m.askSteps(steps)
 	var load func(string) ([]byte, error)
-	if m.ReadSteps.Get != nil {
-		load = func(key string) ([]byte, error) { return m.ReadSteps.Get(key) }
+	if m.ReadPauses.Get != nil {
+		load = func(key string) ([]byte, error) { return m.ReadPauses.Get(key) }
 	}
-	return &buildstep.Puller{Source: source, Language: delivery.AskNode, Node: m.Node, Put: m.Steps, Load: load,
+	return &buildstep.Puller{Source: source, Language: delivery.AskNode, Node: m.Node, Put: m.Steps, PausePut: m.Pauses, Load: load,
 		Capacity: capacity, WatchConfig: watch, Logf: m.Say,
 		Run: func(ctx context.Context, a delivery.StepAsk) (any, error) {
 			if err := m.Prepare(ctx); err != nil {

modules/mesh-build-node/cmd/mesh-build-node/main.go

@@ -46,6 +46,8 @@ func main() {
 		Emit:                func(t string, b any) error { return stdio.Emit(t, b) },
 		Steps:               stdio.State(delivery.StepsState).Put,
 		ReadSteps:           readOf(stdio.State(delivery.StepsState)),
+		Pauses:              stdio.State(delivery.PausesState).Put,
+		ReadPauses:          readOf(stdio.State(delivery.PausesState)),
 		ReadToolchainsState: readOf(stdio.State(delivery.ToolchainsState)),
 		Work:                WorkDir,
 		Run:                 forgekey.ExecRunnerClean(0),

modules/mesh-build-node/cmd/mesh-build-node/manifest_test.go

@@ -94,9 +94,13 @@ func TestManifestKeepsItsStatesClaimsItsBuildSeatAndDeclaresItsHealthTool(t *tes
 	states := []string{}
 	for _, s := range m.State {
 		states = append(states, s.Name)
+		// A step's key is per step and dropped after its age, so the bucket cannot fill; a pause has no age.
+		if (s.Name == "steps") != (s.TTLSeconds > 0) {
+			t.Errorf("state %s has ttl-seconds %d: only steps has an age", s.Name, s.TTLSeconds)
+		}
 	}
 	slices.Sort(states)
-	if want := []string{"keys", "steps", "toolchains"}; !slices.Equal(states, want) {
+	if want := []string{"keys", "pauses", "steps", "toolchains"}; !slices.Equal(states, want) {
 		t.Errorf("state = %v, want %v", states, want)
 	}
 	if len(m.Claims) != 1 || m.Claims[0].Name != Seat || !slices.Equal(m.Claims[0].Serves, []string{"current", "pause", "resume"}) {

modules/mesh-build-node/cmd/mesh-build-node/module.go

@@ -43,6 +43,9 @@ type Module struct {
 	Toolchains, Steps buildstep.Put
 	// ReadSteps and ReadToolchainsState read those two states back for the read tools (issue 1562).
 	ReadSteps, ReadToolchainsState StateRead
+	// Pauses is the Put of the pauses state, which keeps the node's pause key without an age; ReadPauses reads it back.
+	Pauses     buildstep.Put
+	ReadPauses StateRead
 	// Emit tells the bus an event (stdio.Emit); nil emits nothing. The guard emits toolchain.reported after each write of
 	// the toolchains key, so the indexer, which holds no timer, learns that the bucket exists (issue 1444).
 	Emit func(eventType string, body any) error