Compare a build with the one the mesh registered, not the newest, which may be one put back (review of #336, hq issue 721)

internal/inventory/builds.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"errors"
 	"sort"
+	"strings"
 	"time"
 
 	"github.com/jackc/pgx/v5"
@@ -301,6 +302,51 @@ func (i *Inventory) Held(ctx context.Context) (map[string]string, error) {
 	return held, nil
 }
 
+// RegisteredHeld is Held narrowed to the build each module has registered (novox/hq issue 721): an artifact is kept
+// only when its reference's digest is in the manifest the module table holds for it, which is what its machines are
+// sent. After a gate failed and the mesh put the earlier build back (RestoreModule), the newest successful build is
+// not what runs, and its artifacts are left out here, so nothing is compared with them.
+func (i *Inventory) RegisteredHeld(ctx context.Context) (map[string]string, error) {
+	held, err := i.Held(ctx)
+	if err != nil {
+		return nil, err
+	}
+	rows, err := i.store.Pool().Query(ctx, `select name, coalesce(manifest::text, '') from module`)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	registered := map[string]string{}
+	for rows.Next() {
+		var name, manifest string
+		if err := rows.Scan(&name, &manifest); err != nil {
+			return nil, err
+		}
+		registered[name] = manifest
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return registeredOnly(held, registered), nil
+}
+
+// registeredOnly keeps of held each "<module>/<artifact>" whose reference's digest the module's registered manifest
+// names.
+func registeredOnly(held, registered map[string]string) map[string]string {
+	out := map[string]string{}
+	for key, ref := range held {
+		module, _, ok := strings.Cut(key, "/")
+		at := strings.LastIndex(ref, "@")
+		if !ok || at < 0 || len(ref) <= at+1 {
+			continue
+		}
+		if strings.Contains(registered[module], ref[at+1:]) {
+			out[key] = ref
+		}
+	}
+	return out
+}
+
 // BuiltAgainst is what each module's newest successful build stood on, as recorded — the build
 // edges (ADR 0009). A module whose last build recorded no bases is absent, which is also what a
 // module standing on nothing looks like: an edge the mesh has not derived is not an edge.