Put back on a failed gate only a build of the module's own repository

A build refused for its repository is still recorded, and a fork carries the
commit the module was registered at: the rollback's search for the previous
build would have found it and registered it by the back door.

cmd/mesh-controller/build_source_test.go

@@ -184,3 +184,39 @@ func asTheOperator(t *testing.T, inv *inventory.Inventory, b link.BuildResult) l
 	}
 	return b
 }
+
+// A rollback puts back only a build of the module's own repository: an agent's build of the module's name,
+// recorded and refused, at the very commit the machine ran before (a fork carries it), is never registered by
+// the back door of a failed gate.
+func TestARollbackNeverPutsBackABuildFromAnotherRepository(t *testing.T) {
+	open := theCatalogue(t)
+	ctx := t.Context()
+	inv := open.inventory
+	fork := onTrunk("build-1791500000000000000", "agent/mesh-catalog", "git", "modules/sudo",
+		map[string]any{"module": "sudo", "version": "evil"})
+	fork.Commit = "c0ffee0123456789" // the commit sudo was registered at
+	keptAsked(t, inv, fork.ID, "agent/mesh-catalog", false)
+	if _, _, err := takeIn(ctx, inv, fork); !errors.Is(err, errNotItsSource) {
+		t.Fatalf("the fork's build was taken in: %v", err)
+	}
+	failed := onTrunk("build-1791600000000000000", "novox/mesh-catalog", "git", "modules/sudo",
+		map[string]any{"module": "sudo", "version": "2"})
+	failed.Commit = "badbadbad0123456"
+	if _, _, err := takeIn(ctx, inv, failed); err != nil {
+		t.Fatal(err)
+	}
+	record, _, err := inv.BuildByID(ctx, failed.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	previous, found, err := inv.PreviousBuild(ctx, "sudo", "c0ffee0123456789", record)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if found && previous.ID == fork.ID {
+		t.Fatalf("a rollback would put back the fork's build %s", previous.ID)
+	}
+	if !found || previous.ID != "build-sudo" {
+		t.Fatalf("a rollback puts back %q (found %v), want the registered build-sudo", previous.ID, found)
+	}
+}

internal/inventory/gate.go

@@ -7,6 +7,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"strings"
 	"time"
 
 	"github.com/jackc/pgx/v5"
@@ -169,6 +170,12 @@ func (i *Inventory) PreviousBuild(ctx context.Context, module, commit string, fa
 		if b.ID == failed.ID || (commit != "" && b.Commit != commit) {
 			continue
 		}
+		// Only a build of the repository the failed build was made from — the module's, since its take-in
+		// registered it (novox/hq ADR 0266): a build of the module's name from another repository is recorded
+		// and was never registered, and putting it back would register it now.
+		if failed.Repository != "" && !sameRepositoryAs(b.Repository, failed.Repository) {
+			continue
+		}
 		if !failed.AskedOrAt().IsZero() && !b.AskedOrAt().Before(failed.AskedOrAt()) {
 			continue
 		}
@@ -190,6 +197,14 @@ func (i *Inventory) PreviousBuild(ctx context.Context, module, commit string, fa
 	return Build{}, false, nil
 }
 
+// sameRepositoryAs says two recorded repositories are one, however their case or `.git` is spelled.
+func sameRepositoryAs(a, b string) bool {
+	trim := func(s string) string {
+		return strings.TrimSuffix(strings.TrimRight(strings.ToLower(strings.TrimSpace(s)), "/"), ".git")
+	}
+	return trim(a) == trim(b)
+}
+
 // RestoreModule puts a module's registered build back to an earlier one: its manifest, the commit it
 // was built from, and when it was asked — as now, so the build that failed its gate, asked before, can
 // never register over it again (issue 219's order). The source's head is left where the merge moved it: