B7-1: recovery-merged names the branch the merge moved and the module of the record's catalog half

Builds: design 47 G §81, §522, A-161, A-172
Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h

modules/mesh-delivery-gate/cmd/mesh-delivery-gate/record_test.go

@@ -715,6 +715,33 @@ func TestTheRecordsToolsReadThemAndEndOneByHand(t *testing.T) {
 			t.Fatal("a recovery with no why was taken")
 		}
 	})
+	t.Run("recovery-merged names the branch the merge moved and the module its record's catalog half names (design 47 G A-161, A-172)", func(t *testing.T) {
+		var body meshdelivery.RecoveryMergedEvent
+		rs := &Records{Ledger: newLedgerFake(t), Now: func() time.Time { return at },
+			Say: func(subject string, b any, id string) error {
+				if subject == meshdelivery.SubjectRecoveryMerged {
+					body = b.(meshdelivery.RecoveryMergedEvent)
+				}
+				return nil
+			}}
+		commit := strings.Repeat("2", 40)
+		r, _, err := rs.Open(recordMilestone("feat/x", 4), map[string]string{"novox/app@222222222222": commit}, false)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if err := rs.AddEntry(r, RecordEntry{Module: "mesh-y", Fingerprint: "src2:f2"}); err != nil {
+			t.Fatal(err)
+		}
+		if err := rs.AddEntry(r, RecordEntry{Module: "mesh-x", Fingerprint: "src2:f1", Node: "ace"}); err != nil {
+			t.Fatal(err)
+		}
+		if _, err := rs.Recovery("novox/app", commit, "why", "jochen"); err != nil {
+			t.Fatal(err)
+		}
+		if body.Branch != "feat/x" || body.Module != "mesh-y" {
+			t.Fatalf("said %+v", body)
+		}
+	})
 	t.Run("a removal asks the runtime's ledger removal of the instance, and one said twice changes nothing", func(t *testing.T) {
 		was := ledgerCall
 		t.Cleanup(func() { ledgerCall = was })

modules/mesh-delivery-gate/cmd/mesh-delivery-gate/recovery.go

@@ -3,9 +3,11 @@ package main
 import (
 	"errors"
 	"fmt"
+	"sort"
 	"strings"
 
 	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-contracts/go/seats/meshdelivery"
+	"git.novox.be/novox/mesh-sdk/go/keys"
 )
 
 // Recovery names a merge a recovery (design 47 G §81, A-23): the delivery record that holds the commit is marked through its
@@ -36,7 +38,8 @@ func (rs *Records) Recovery(repository, commit, why, by string) (meshdelivery.Re
 			r.Recovery, r.Sequence = &want, seq
 			now := rs.now()
 			if err := rs.say(meshdelivery.SubjectRecoveryMerged, meshdelivery.RecoveryMergedEvent{At: &now, By: by, Commit: head,
-				Repository: repository, V: 1, Why: why}, "recovery-merged."+r.Instance+"."+head); err != nil {
+				Repository: repository, V: 1, Why: why,
+				Branch: branchOf(r), Module: moduleOf(r)}, "recovery-merged."+r.Instance+"."+head); err != nil {
 				return meshdelivery.RecoveryAnswer{}, fmt.Errorf("the record %s is marked but recovery-merged is not said: %w", r.Instance, err)
 			}
 			return meshdelivery.RecoveryAnswer{By: by, Commit: head, Recovery: true, Repository: repository}, nil
@@ -44,3 +47,32 @@ func (rs *Records) Recovery(repository, commit, why, by string) (meshdelivery.Re
 	}
 	return meshdelivery.RecoveryAnswer{}, fmt.Errorf("no delivery record holds %s at %s: the merge is taken in first", repository, commit)
 }
+
+// branchOf is the watched branch a record's merge moved: the record of a taken source revision is keyed `<branch>.<source>`
+// (recordMilestone); a milestone of another form names no branch.
+func branchOf(r *Record) string {
+	part, _, ok := strings.Cut(r.Milestone, ".")
+	if !ok {
+		return ""
+	}
+	branch, err := keys.UnescapeName(part)
+	if err != nil {
+		return ""
+	}
+	return branch
+}
+
+// moduleOf is the module the merge changed, from the entries of the record's catalog half (those that name no node), the
+// modules in order and comma-separated when the merge changed several.
+func moduleOf(r *Record) string {
+	seen := map[string]bool{}
+	var modules []string
+	for _, e := range r.Entries {
+		if e.Node == "" && e.Module != "" && !seen[e.Module] {
+			seen[e.Module] = true
+			modules = append(modules, e.Module)
+		}
+	}
+	sort.Strings(modules)
+	return strings.Join(modules, ", ")
+}