Fix builds:output exiting 0 for unknown build ids

When the per-build log is missing, builds:output fell through to
journalctl without checking that the build record exists. A typo'd or
never-recorded id then printed nothing and exited 0.

Validate the build record first and return "no such build" when it is
absent. Existing records with pruned logs still use the journalctl
fallback.

Fixes #9031

plugins/builds/builds_test.go

@@ -609,3 +609,53 @@ func TestBuildJSONShape(t *testing.T) {
 		t.Errorf("kind not serialized as enum string: %s", string(raw))
 	}
 }
+
+func setupTestAppRoot(t *testing.T, libRoot, appName string) {
+	t.Helper()
+	dokkuRoot := filepath.Join(libRoot, "dokku-root")
+	if err := os.MkdirAll(filepath.Join(dokkuRoot, appName), 0755); err != nil {
+		t.Fatalf("mkdir app root: %v", err)
+	}
+	t.Setenv("DOKKU_ROOT", dokkuRoot)
+}
+
+func TestCommandOutputRejectsUnknownBuildID(t *testing.T) {
+	tmp := setupTestRoot(t)
+	app := "demo"
+	setupTestAppRoot(t, tmp, app)
+
+	err := CommandOutput(app, "not-a-real-build-id")
+	if err == nil {
+		t.Fatal("expected error for unknown build id")
+	}
+	want := "no such build not-a-real-build-id for app demo"
+	if err.Error() != want {
+		t.Fatalf("got %q, want %q", err.Error(), want)
+	}
+}
+
+func TestCommandOutputMissingLogWithRecordDoesNotClaimUnknown(t *testing.T) {
+	tmp := setupTestRoot(t)
+	app := "demo"
+	setupTestAppRoot(t, tmp, app)
+
+	b := Build{
+		ID:        "abc123xyz00001",
+		App:       app,
+		Kind:      BuildKindBuild,
+		PID:       1,
+		StartedAt: time.Now().UTC().Truncate(time.Second),
+		Status:    BuildStatusSucceeded,
+		Source:    BuildSourceGitHook,
+	}
+	if err := WriteBuild(b); err != nil {
+		t.Fatalf("WriteBuild: %v", err)
+	}
+
+	err := CommandOutput(app, b.ID)
+	if err != nil && strings.Contains(err.Error(), "no such build") {
+		t.Fatalf("existing record should not be reported unknown: %v", err)
+	}
+	// Without a log file, the next step is journalctl (or a clear "not available"
+	// error). Either outcome is fine; the regression is the false "success".
+}

plugins/builds/subcommands.go

@@ -381,6 +381,14 @@ func CommandOutput(appName, buildID string) error {
 	logPath := LogPathFor(appName, buildID)
 	if _, err := os.Stat(logPath); err != nil {
 		if os.IsNotExist(err) {
+			// A missing log is normal after prune/rotation, but a typo'd or
+			// never-recorded id must not fall through to journalctl and exit 0.
+			if _, err := ReadBuild(appName, buildID); err != nil {
+				if os.IsNotExist(err) {
+					return fmt.Errorf("no such build %s for app %s", buildID, appName)
+				}
+				return err
+			}
 			return outputViaJournalctl(buildID)
 		}
 		return err