Let a drain lapse, bound the gate's wait on the controller's clock, keep a busy wait out of apply time

Review of #283: a drain whose replacement was withdrawn held the agent for
ever with its health green; the gate trusted the engine's until; a machine
of the rest waiting at the bound read as silent and its apply time held the
wait; an unknown mesh-builder word exited 0; plan said nothing of a busy an
older engine is not sent; and a node with a report and no send broke the
reading of every last report (the store test's NULL).

cmd/mesh-controller/busy_test.go

@@ -5,6 +5,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/novox/mesh-controller/internal/catalogue"
 	"github.com/novox/mesh-controller/internal/inventory"
 )
 
@@ -109,3 +110,39 @@ func TestAGateOfAnEngineThatNeverWaitsStartsAsBefore(t *testing.T) {
 		t.Fatal("a wait reported about an earlier declaration held the gate")
 	}
 }
+
+// The wait is bounded on this controller's clock: an engine whose clock runs an hour ahead, saying it waits until
+// then, holds the gate no longer than 15 minutes and the slack from when the controller first read the wait.
+func TestAGateWaitIsBoundedOnTheControllersClock(t *testing.T) {
+	seen := time.Date(2026, 10, 13, 1, 0, 0, 0, time.UTC)
+	g := &inventory.PlanGate{Machines: []string{"novox"}, Since: &seen}
+	pairs := []judged{{module: "build-agent", node: "novox"}}
+	ahead := seen.Add(time.Hour)
+	f := gateFacts{reports: map[string]inventory.Reported{"novox": {Node: "novox", Outcome: inventory.OutcomeApplied,
+		At: &seen, Current: true, Busy: []inventory.BusyWait{{ID: "build-agent.server", Container: "mesh-build-agent",
+			State: inventory.BusyWaiting, Since: ahead, Until: ahead.Add(15 * time.Minute)}}}}}
+	if !busyWait(g, pairs, f, seen) || !g.Busy.Seen.Equal(seen) {
+		t.Fatalf("the gate did not start waiting, seen now: %+v", g.Busy)
+	}
+	if !busyWait(g, pairs, f, seen.Add(15*time.Minute+busyGateSlack-time.Second)) {
+		t.Fatal("the gate stopped waiting within the bound on its own clock")
+	}
+	if busyWait(g, pairs, f, seen.Add(15*time.Minute+busyGateSlack+time.Second)) || !g.Busy.PastBound {
+		t.Fatalf("an engine's later word held the gate past the controller's bound: %+v", g.Busy)
+	}
+}
+
+// `plan` says, for a machine whose node-engine is older than the field, each container whose busy is not sent.
+func TestAPlanSaysABusyAnOlderEngineIsNotSent(t *testing.T) {
+	modules := []catalogue.Manifest{{Module: "build-agent", Resources: []map[string]any{
+		{"id": "server", "type": "container", "busy": map[string]any{"command": "mesh-builder busy"}},
+		{"id": "agent-env", "type": "file"}}}}
+	lines := busyNotSent(modules, false)
+	if len(lines) != 1 || !strings.Contains(lines[0], "build-agent.server declares busy") ||
+		!strings.Contains(lines[0], "replaced at once") {
+		t.Fatalf("the plan does not say the busy not sent: %v", lines)
+	}
+	if lines := busyNotSent(modules, true); len(lines) != 0 {
+		t.Fatalf("a busy sent is said as not sent: %v", lines)
+	}
+}