Ask the plans again when the moved path starts before its runtime answers (issue 943)

postgres and keycloak start their moved path beside Serve, and a watch
asked before Serve runs is refused by the runtime. Run returned on that
refusal and main only logged it, so a start that lost the race left the
provider answering nobody and retiring nothing until its next restart:
postgres on novox at 16:52, 18:29 and 18:48, on ace at 16:22, which kept
issue 937's retirement condition on novox from clearing. Run now asks
again, the wait doubling from a second to a minute, until the runtime
answers or its context ends.

modules/postgres/cmd/postgres-provider/early_test.go

@@ -0,0 +1,62 @@
+package main
+
+// The moved path started before its runtime answers asks again until it does (issue 943).
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/provider"
+)
+
+// earlyBus refuses its first watches as the runtime does before Serve runs, then answers as the bucket bus does.
+type earlyBus struct {
+	*bucketBus
+	refuse int
+}
+
+func (b *earlyBus) Watch(ctx context.Context, bucket string, handle func(string, []byte)) error {
+	if b.refuse > 0 {
+		b.refuse--
+		return errors.New("before Serve: a bundle reaches the bus through the runtime that launched it")
+	}
+	return b.bucketBus.Watch(ctx, bucket, handle)
+}
+
+func TestAMovedPathStartedTooEarlyAsksAgainUntilTheRuntimeAnswers(t *testing.T) {
+	w := newMovedWorld(t, map[[2]string]string{})
+	w.run.FirstRetry = time.Millisecond
+	w.run.loaded = false
+	bus := &earlyBus{bucketBus: w.bus, refuse: 3}
+	p := provider.New(provider.Options{Node: "novox", Module: "postgres", Bus: w.bus,
+		Vault: provider.ConsumersFile{Paths: []string{w.file}}, Make: w.run.Make, Gone: w.run.Gone,
+		Every: time.Hour, Logf: func(string, ...any) {}})
+	ctx, cancel := context.WithCancel(context.Background())
+	done := make(chan error, 1)
+	go func() { done <- w.run.Run(ctx, p, bus) }()
+	deadline := time.After(time.Second)
+	for {
+		w.run.mu.Lock()
+		loaded := w.run.loaded
+		w.run.mu.Unlock()
+		if loaded {
+			break
+		}
+		select {
+		case err := <-done:
+			cancel()
+			t.Fatalf("Run stopped before the runtime answered: %v", err)
+		case <-deadline:
+			cancel()
+			t.Fatal("the plans were never watched")
+		case <-time.After(time.Millisecond):
+		}
+	}
+	cancel()
+	<-done
+	if bus.refuse != 0 {
+		t.Fatalf("%d refusals left", bus.refuse)
+	}
+}