CT10: a branch with no revision yet is a ready, empty catalog view

Builds: design 47 G §479, §495

Claude-Session: https://claude.ai/code/session_01JG73KEq4zoDfM9WtYpcQgZ

contracts/go/clients/meshcatalogclient/catalog.go

@@ -3,9 +3,11 @@ package meshcatalogclient
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"maps"
 	"strconv"
+	"strings"
 	"sync"
 	"time"
 
@@ -174,6 +176,10 @@ func (c *Catalog) ask(_ context.Context, after string) (views.Answer, error) {
 	}
 	c.mu.Unlock()
 	a, err := askRevision(c.call, in)
+	if errors.Is(err, errNoneYet) {
+		// A branch with no revision yet is ready and empty, and nothing waits for it (§479, §495).
+		return views.Answer{V: 1, Owner: seat.Seat, State: c.Follower.State, Created: catalogCreated, Values: map[string]json.RawMessage{}, At: time.Now()}, nil
+	}
 	if err != nil {
 		return views.Answer{}, err
 	}
@@ -210,13 +216,22 @@ func (c *Catalog) ask(_ context.Context, after string) (views.Answer, error) {
 	return views.Answer{V: 1, Owner: seat.Seat, State: c.Follower.State, Revision: uint64(rev), Created: catalogCreated, Values: values, Next: a.Next, At: time.Now()}, nil
 }
 
+// errNoneYet is the seat's answer `none yet`: the branch has no revision yet.
+var errNoneYet = errors.New("none yet")
+
 func askRevision(call Call, in seat.RevisionInput) (seat.RevisionAnswer, error) {
 	raw, err := call(RevisionVerb, in)
 	if err != nil {
+		if strings.Contains(err.Error(), views.NoneYet) {
+			return seat.RevisionAnswer{}, errNoneYet
+		}
 		return seat.RevisionAnswer{}, err
 	}
 	answer, said, ok := buscalls.Unwrap(raw)
 	if !ok {
+		if strings.Contains(said, views.NoneYet) {
+			return seat.RevisionAnswer{}, errNoneYet
+		}
 		return seat.RevisionAnswer{}, fmt.Errorf("%s answered: %s", RevisionVerb, said)
 	}
 	var a seat.RevisionAnswer

contracts/go/clients/meshcatalogclient/catalog_view_test.go

@@ -27,6 +27,9 @@ func (f *fakeRevisions) call(key string, body any) (json.RawMessage, error) {
 	f.mu.Lock()
 	defer f.mu.Unlock()
 	rev, ok := f.newest[in.Branch]
+	if ok && rev == 0 {
+		return nil, fmt.Errorf("revision of %s: none yet", in.Branch)
+	}
 	if !ok {
 		return nil, fmt.Errorf("asked for the branch %q", in.Branch)
 	}
@@ -136,6 +139,20 @@ func TestCatalogIsAViewPerWatchedBranch(t *testing.T) {
 		t.Errorf("the gap was not said in the log: %q", logged)
 	}
 
+	// A branch with no revision yet is ready and empty, and nothing waits for it.
+	f.set("new", 0)
+	none, err := NewCatalog(f.call, "new")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := none.Start(ctx); err != nil {
+		t.Fatal(err)
+	}
+	<-none.Ready()
+	if _, ok := none.View(); ok || none.Follower.Status().WaitsFor != "" {
+		t.Errorf("a branch with no revision yet holds a view or waits: %+v", none.Follower.Status())
+	}
+
 	for _, data := range []string{`{}`, `not json`} {
 		if err := main.Hear(ctx, []byte(data)); err == nil {
 			t.Errorf("Hear(%s) took it", data)