indexer: before the pending state is on the bus, take a merge in at once and start without asking the own build (ADR 0633, issue 1585)

TestIndexerWhole found the start waiting for ever on a build no node-engine
answered, so the forge consumer never started, though nothing can be pending.

Claude-Session: https://claude.ai/code/session_01JG73KG7AfSdh6FP8VrBqCn

modules/mesh-delivery-indexer/internal/index/pending.go

@@ -192,6 +192,14 @@ func revisionWait(kind string, ready []PendingEntry, waitsFor string) delivery.T
 		WaitsFor: waitsFor, Since: sinceOf(ready)}
 }
 
+// pendingOnBus says whether the pending state is on the bus: a state this delivery brings is bound when it appears
+// (issue 1790), and until then every merge is taken in at once, so the build this program runs is not needed. A read
+// that fails otherwise counts as on the bus: the step that follows answers the error.
+func (ix *Indexer) pendingOnBus(ctx context.Context) bool {
+	_, _, _, err := ix.Pending.Get(ctx, delivery.PendingKey(0))
+	return !errors.Is(err, process.ErrNotYet)
+}
+
 // ownBuildNow is the build this program runs: the one learnt, else asked of the node-engine now.
 func (ix *Indexer) ownBuildNow(ctx context.Context) string {
 	ix.ownMu.Lock()
@@ -246,7 +254,9 @@ func (ix *Indexer) markSaid(ctx context.Context, entries []PendingEntry, t *deli
 // indexer it names. It answers what was taken in, and a line saying what waits. A message is never written while the
 // build this program runs is not known (ErrOwnBuildUnknown).
 func (ix *Indexer) Arrive(ctx context.Context, seq uint64, f delivery.Forge) (Applied, string, error) {
-	if ix.Pending == nil || ix.Modules == nil {
+	if ix.Pending == nil || ix.Modules == nil || !ix.pendingOnBus(ctx) {
+		// The state this delivery brings is not on the bus yet (issue 1790): the merge is taken in at once, as before,
+		// whether or not the build this program runs is known.
 		a, err := ix.ApplyMessage(ctx, f)
 		return a, "", err
 	}
@@ -295,7 +305,7 @@ func (ix *Indexer) Arrive(ctx context.Context, seq uint64, f delivery.Forge) (Ap
 // the member arrived. An end of a group taken in already (every member's merge at or behind its repository's taken
 // merge) changes nothing and is said: it is never delivered again for ever.
 func (ix *Indexer) EndGroup(ctx context.Context, end delivery.ForgeGroupEnd) (Applied, string, error) {
-	if ix.Pending == nil {
+	if ix.Pending == nil || !ix.pendingOnBus(ctx) {
 		return Applied{}, "no pending state: the group's merges were taken in one by one", nil
 	}
 	own := ix.ownBuildNow(ctx)
@@ -388,8 +398,9 @@ func (ix *Indexer) takenAlready(ctx context.Context, m delivery.GroupMerge) (boo
 // pending, taking in the whole revisions that name this build; a group still being gathered stays, and a revision
 // naming yet another build is held for that one. A claim left by an indexer that ran before is void here.
 func (ix *Indexer) TakeInAtStart(ctx context.Context, wait func(context.Context) bool) (Applied, string, error) {
-	if ix.Pending == nil {
-		return Applied{}, "", nil
+	if ix.Pending == nil || !ix.pendingOnBus(ctx) {
+		// Nothing can wait in a state not on the bus: the start asks no build and does not wait for one.
+		return Applied{}, "the pending state is not on the bus yet: nothing waits", nil
 	}
 	own := ix.ownBuildNow(ctx)
 	for own == "" {

modules/mesh-delivery-indexer/internal/index/pending_test.go

@@ -10,6 +10,7 @@ import (
 	"testing"
 
 	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/process"
 )
 
 // takeInBed is an indexer holding the catalogue's avahi and the indexer's own module, both with a fingerprint, its
@@ -112,6 +113,15 @@ func TestTakeIn(t *testing.T) { // 1585/T3-T13 (ADR 0633)
 		if !errors.Is(err, ErrOwnBuildUnknown) || len(b.keys()) != 0 || b.commit(t, "avahi") == sha('b') {
 			t.Errorf("err %v, pending %v, avahi at %s: want ErrOwnBuildUnknown and nothing written", err, b.keys(), b.commit(t, "avahi"))
 		}
+		// Before the pending state is on the bus nothing waits: the start asks no build, and the merge is taken in at once,
+		// as before ADR 0633, though the build is unknown (TestIndexerWhole found the start waiting on it for ever).
+		b.ix.Pending = &memStore{unbound: process.ErrNotYet}
+		if _, _, err := b.ix.TakeInAtStart(ctx, func(context.Context) bool { t.Fatal("the start waits for the build"); return false }); err != nil {
+			t.Fatal(err)
+		}
+		if _, _, err := b.ix.Arrive(ctx, 1, b.merge(20, sha('b'), "tree-avahi-2", "")); err != nil || b.commit(t, "avahi") != sha('b') {
+			t.Errorf("no pending state: err %v, avahi at %s: want the merge taken in at once", err, b.commit(t, "avahi"))
+		}
 	})
 	t.Run("T7 and T3 a merge alone, an indexer change, a merge behind it and a revert", func(t *testing.T) {
 		b := newTakeInBed(t)