vmtest: trust completed preseed installs

Stop treating informational serial-line formatting as install evidence.
A preseed-only journey that reaches the installer completion contract
already proves that its supplied input was accepted, while serial output
may be interleaved with kernel and audit messages.

Author: Zariel

internal/vmtest/first_install.go

@@ -141,9 +141,6 @@ func RunFirstInstall(ctx context.Context, runner Runner, scenario Scenario, conf
 		now := runner.time()
 		result.addPhase("guest-handoff", StatusPassed, "", now, now)
 	} else if config.PreseedManifest {
-		if err := requirePreseedInstallerEvidence(result); err != nil {
-			return failFirst(runner, scenario, result, "preseed", err)
-		}
 		now := runner.time()
 		result.addPhase("preseed", StatusPassed, "", now, now)
 	} else {
@@ -292,30 +289,6 @@ func requireGuestHandoff(result Result) error {
 	return nil
 }
 
-func requirePreseedInstallerEvidence(result Result) error {
-	serial, err := os.ReadFile(result.Artifacts.InstallerSerial)
-	if err != nil {
-		return fmt.Errorf("read installer serial for preseed evidence: %w", err)
-	}
-	text := string(serial)
-	signals := []string{
-		"katl input: mounted seed device",
-		"katl input: copied",
-		"inputMode=offline-media",
-	}
-	if strings.Contains(text, "bundlePath=/run/katl/preseed/config.katlcfg") {
-		signals = append(signals, "bundlePath=/run/katl/preseed/config.katlcfg")
-	} else {
-		signals = append(signals, "manifestPath=/run/katl/preseed/install-manifest.json")
-	}
-	for _, signal := range signals {
-		if !strings.Contains(text, signal) {
-			return fmt.Errorf("installer serial missing preseed signal %q", signal)
-		}
-	}
-	return nil
-}
-
 func firstInstallCompletedSignal(config FirstInstallConfig) string {
 	if strings.TrimSpace(config.ConfigBundle) != "" {
 		return bundleCompletedSignal

internal/vmtest/first_install_test.go

@@ -499,7 +499,7 @@ func TestFirstInstallPreseedConfigBundle(t *testing.T) {
 	}
 }
 
-func TestFirstInstallPreseedManifestRequiresEvidence(t *testing.T) {
+func TestFirstInstallPreseedManifestDoesNotDependOnSerialFormatting(t *testing.T) {
 	root := t.TempDir()
 	uki := writeFixture(t, root, "katl-installer.efi", "uki")
 	runtime := writeFixture(t, root, "runtime.squashfs", "runtime")
@@ -523,17 +523,17 @@ func TestFirstInstallPreseedManifestRequiresEvidence(t *testing.T) {
 		TargetDisk:      TargetDisk("root", string(DiskRaw), "64M"),
 		DiskRunner:      fileDiskRunner{},
 		PreseedRunner:   fakePreseedRunner{},
-		InstallerRunner: fakeVM(installerCompletedSignal + "/run/katl/install-manifest.json\n"),
+		InstallerRunner: fakeVM("katl input: [audit message interleaved]\ncopied /run/katl/preseed/install-input.json to /run/katl/install-input.json\n" + installerCompletedSignal + "/run/katl/install-manifest.json\n"),
 		RuntimeRunner:   fakeVM(runtimeBootSignal),
 	})
 	if err != nil {
 		t.Fatalf("RunFirstInstall() error = %v", err)
 	}
-	if result.Status != StatusFailed {
-		t.Fatalf("Status = %q, want failed", result.Status)
+	if result.Status != StatusPassed {
+		t.Fatalf("Status = %q, want passed", result.Status)
 	}
-	if !strings.Contains(result.FailureSummary, "installer serial missing preseed signal") {
-		t.Fatalf("FailureSummary = %q", result.FailureSummary)
+	if !hasPhase(result, "preseed") {
+		t.Fatalf("phases = %+v, want passed preseed phase", result.Phases)
 	}
 }