Check the migration actually kept everything, and let report say so

internal/validate was written and tested and then never called: `run` ended
at cutover, so the tool performed a migration and never confirmed it had
carried the data across, and `report` was an error message pointing at the
package that would have answered.

`run` now compares the migrated instance against the snapshot preflight took
and fails if an account or a domain that existed before is missing from it.
The comparison runs against the service cutover has just started, which is
the instance people will actually use - its real config, its real ports,
under its real service manager - and costs no extra downtime; booting a
second copy inside the maintenance window would. BootCheck stays as the
equivalent for an instance the tool boots itself.

The service is left running on a failure. By that point the store has been
migrated in place, so stopping it undoes nothing, and only the operator can
weigh the finding against their recovery point.

A check that could not run is reported as skipped, never as a pass. Preflight
only captures the "before" when it has an admin URL, and a run without one
has to say it compared nothing rather than imply everything survived - which
is the exact failure ARCHITECTURE.md §4.7 warns about. `report <run-id>`
re-reads the recorded verdict rather than re-checking: run again next week
and you would be asking how the instance looks now, not how it looked when
it was migrated.

§4.7 said validation ran after cutover while the only implementation booted
its own copy, and listed a suite far larger than what exists. It now says
which of the two happens, and which checks are real.

ARCHITECTURE.md

@@ -340,9 +340,26 @@ no-data-loss guarantee that was not measured. See
 `internal/validate/content_integrity.go`.
 
 
-Runs automatically after cutover; failure here stops the run, reports
+Runs automatically after cutover, against the service cutover has just
-loudly, and exits non-zero, leaving the operator to decide what to restore
+started: that is the instance people will actually use — its real config,
-(§4.8).
+its real ports, under its real service manager — and checking it costs no
+extra downtime, where booting a second copy inside the maintenance window
+would. Failure stops the run, reports loudly, and exits non-zero, leaving
+the operator to decide what to restore (§4.8). The service is deliberately
+left running: by this point the store has been migrated in place, so
+stopping it undoes nothing.
+
+A check that could not be performed is reported as **skipped**, never as a
+pass. Preflight only captures the "before" snapshot when it has an admin URL
+to capture it from, and a run without one has to say it compared nothing
+rather than imply everything survived.
+
+`internal/validate.BootCheck` remains the equivalent for an instance the
+tool boots itself, which is what `rehearse` needs; `run` uses `RunLive`.
+
+Of the checks listed below, what exists today is the account/domain
+comparison. The rest are the intended shape of the suite, not a description
+of it.
 
 - **Version check**: reported server version matches the target exactly.
 - **Auth check**: WebUI login succeeds over the *configured hostname* via

README.md

@@ -22,10 +22,11 @@ has been performed end to end.
 | `stalwart-migrate rehearse` | **Works** — read-only; converts your settings and reports what won't carry over |
 | `stalwart-migrate run` | **Works** — performs the migration; `--recovery-point-confirmed --yes` |
 | `stalwart-migrate status <id>` | **Works** |
-| `stalwart-migrate report <id>` | Not implemented |
+| `stalwart-migrate report <id>` | **Works** — prints what validation found for a run |
 
 **`run` performs the migration**, in the order
-preflight → stage → dump → stop → convert → recovery-mode → cutover. It
+preflight → stage → dump → stop → convert → recovery-mode → cutover →
+validate. It
 needs two flags: `--yes` (intent) and `--recovery-point-confirmed` (a claim
 that you have a snapshot or backup you have verified you can restore — this
 tool cannot undo a migration and will not start without it).
@@ -37,6 +38,14 @@ Measured on a full migration: the store converts in seconds, and the service
 was down for **6 seconds** end to end. Plan the window around verification,
 not data volume.
 
+After cutover, `run` compares the migrated instance against the snapshot
+preflight took, and fails the command if an account or a domain that existed
+before is missing from it. The service is left running either way — by that
+point the store has been migrated in place, so stopping it would not undo
+anything; your recovery point is the way back. `report <run-id>` prints the
+same finding again later. Where preflight had no admin URL to snapshot from,
+validation reports itself as skipped rather than passed.
+
 Package state:
 
 Lines are implementation only; each package carries its tests alongside.

cmd/stalwart-migrate/main.go

@@ -30,7 +30,7 @@ func main() {
 	case "status":
 		err = runStatus(os.Args[2:])
 	case "report":
-		err = fmt.Errorf("not implemented yet: see internal/validate")
+		err = runReport(os.Args[2:])
 	default:
 		usage()
 		os.Exit(1)
@@ -50,5 +50,5 @@ commands:
   rehearse    convert this instance's settings and report what will NOT carry over (read-only)
   run         perform the migration (needs --yes and --recovery-point-confirmed)
   status      show the state of an in-progress or completed run
-  report      print the validation report for a run (not implemented yet)`)
+  report      print the validation report for a run`)
 }

cmd/stalwart-migrate/report.go

@@ -0,0 +1,93 @@
+// SPDX-FileCopyrightText: 2026 LINUXexpert-org
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package main
+
+import (
+	"flag"
+	"fmt"
+
+	"github.com/LINUXexpert-org/stalwart-migrator/internal/checkpoint"
+	"github.com/LINUXexpert-org/stalwart-migrator/internal/validate"
+)
+
+// runReport prints what validation found for a run, from the checkpoint the
+// run already wrote. It re-reads rather than re-checks: the comparison is
+// against a pre-migration snapshot, so running it again later would answer a
+// different question — how the instance looks now, not how it looked when it
+// was migrated.
+func runReport(args []string) error {
+	fs := flag.NewFlagSet("report", flag.ExitOnError)
+	stateDir := fs.String("state-dir", checkpoint.DefaultBaseDir, "directory runs are checkpointed in")
+
+	runID, rest := splitRunID(fs, args)
+	if err := fs.Parse(rest); err != nil {
+		return err
+	}
+	if fs.NArg() != 0 || runID == "" {
+		return fmt.Errorf("usage: stalwart-migrate report <run-id> [flags]")
+	}
+
+	store := checkpoint.NewStore(*stateDir)
+	rs, err := store.Load(runID)
+	if err != nil {
+		return fmt.Errorf("load run %s: %w", runID, err)
+	}
+
+	report := reportFromSteps(rs)
+	fmt.Printf("run:    %s\n", rs.RunID)
+	fmt.Printf("source: %s\n", rs.SourceVersion)
+	fmt.Printf("target: %s\n", rs.TargetVersion)
+
+	if len(report.Results) == 0 {
+		fmt.Println("\nno validation has been recorded for this run.")
+		if rs.PreflightSnapshot == nil {
+			fmt.Println("preflight captured no pre-migration snapshot, so there was nothing to compare against;")
+			fmt.Println("pass --admin-url to preflight next time and the comparison becomes possible.")
+		} else {
+			fmt.Println("the run did not reach the validate phase - see `stalwart-migrate status " + runID + "`.")
+		}
+		return nil
+	}
+
+	fmt.Println("\nvalidation:")
+	fmt.Print(report.String())
+	if report.Blocking() {
+		// Non-zero so this is usable in a script that gates on it, and so a
+		// failed migration cannot look successful to anything watching.
+		return fmt.Errorf("validation recorded a failure for run %s", runID)
+	}
+	return nil
+}
+
+// reportFromSteps rebuilds the validation report from the checkpointed
+// steps, so the report survives the process that produced it.
+func reportFromSteps(rs *checkpoint.RunState) validate.Report {
+	var report validate.Report
+	for _, step := range rs.Steps {
+		if step.Phase != checkpoint.PhaseValidate {
+			continue
+		}
+		status := validate.StatusOK
+		switch {
+		case step.Error != "":
+			status = validate.StatusFail
+		case step.Verdict == string(validate.StatusFail):
+			status = validate.StatusFail
+		case step.Verdict == string(validate.StatusSkip):
+			status = validate.StatusSkip
+		case step.Status != checkpoint.StepDone:
+			// Recorded but never completed: the run stopped partway.
+			status = validate.StatusFail
+		}
+		detail := step.Detail
+		if step.Error != "" {
+			if detail != "" {
+				detail += " "
+			}
+			detail += "(error: " + step.Error + ")"
+		}
+		report.Results = append(report.Results, validate.CheckResult{Name: step.Name, Status: status, Detail: detail})
+	}
+	return report
+}

cmd/stalwart-migrate/report_test.go

@@ -0,0 +1,102 @@
+// SPDX-FileCopyrightText: 2026 LINUXexpert-org
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package main
+
+import (
+	"testing"
+
+	"github.com/LINUXexpert-org/stalwart-migrator/internal/checkpoint"
+	"github.com/LINUXexpert-org/stalwart-migrator/internal/validate"
+)
+
+// `report` re-reads what the run recorded rather than re-checking, so the
+// mapping from checkpointed step back to verdict is the whole command. The
+// case that matters is a failure staying a failure: a migration that lost an
+// account must not read as clean the next morning.
+
+func TestReportFromSteps(t *testing.T) {
+	for _, tc := range []struct {
+		name  string
+		step  checkpoint.StepRecord
+		want  validate.Status
+		block bool
+	}{
+		{
+			name: "a completed comparison is a pass",
+			step: checkpoint.StepRecord{Phase: checkpoint.PhaseValidate, Name: "content-integrity", Status: checkpoint.StepDone, StepOutcome: checkpoint.StepOutcome{Detail: "12 accounts checked"}},
+			want: validate.StatusOK,
+		},
+		{
+			name:  "a failing verdict survives the round trip",
+			step:  checkpoint.StepRecord{Phase: checkpoint.PhaseValidate, Name: "content-integrity", Status: checkpoint.StepDone, StepOutcome: checkpoint.StepOutcome{Verdict: string(validate.StatusFail), Detail: "missing accounts: [email protected]"}},
+			want:  validate.StatusFail,
+			block: true,
+		},
+		{
+			name: "a skipped check stays skipped, not a pass",
+			step: checkpoint.StepRecord{Phase: checkpoint.PhaseValidate, Name: "content-integrity", Status: checkpoint.StepDone, StepOutcome: checkpoint.StepOutcome{Verdict: string(validate.StatusSkip), Detail: "no snapshot"}},
+			want: validate.StatusSkip,
+		},
+		{
+			name:  "a step that errored is a failure",
+			step:  checkpoint.StepRecord{Phase: checkpoint.PhaseValidate, Name: "content-integrity", Status: checkpoint.StepFailed, Error: "connection refused"},
+			want:  validate.StatusFail,
+			block: true,
+		},
+		{
+			name:  "a step that never finished is a failure, not a pass",
+			step:  checkpoint.StepRecord{Phase: checkpoint.PhaseValidate, Name: "content-integrity", Status: checkpoint.StepRunning},
+			want:  validate.StatusFail,
+			block: true,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			got := reportFromSteps(&checkpoint.RunState{Steps: []checkpoint.StepRecord{tc.step}})
+			if len(got.Results) != 1 {
+				t.Fatalf("got %d results, want 1", len(got.Results))
+			}
+			if got.Results[0].Status != tc.want {
+				t.Fatalf("status = %q, want %q", got.Results[0].Status, tc.want)
+			}
+			if got.Blocking() != tc.block {
+				t.Fatalf("Blocking() = %v, want %v", got.Blocking(), tc.block)
+			}
+		})
+	}
+}
+
+func TestReportFromStepsIgnoresOtherPhases(t *testing.T) {
+	rs := &checkpoint.RunState{Steps: []checkpoint.StepRecord{
+		{Phase: checkpoint.PhaseCutover, Name: "start-service", Status: checkpoint.StepDone},
+		{Phase: checkpoint.PhasePreflight, Name: "disk-space", Status: checkpoint.StepFailed, Error: "nope"},
+		{Phase: checkpoint.PhaseValidate, Name: "content-integrity", Status: checkpoint.StepDone, StepOutcome: checkpoint.StepOutcome{Detail: "ok"}},
+	}}
+	got := reportFromSteps(rs)
+	if len(got.Results) != 1 || got.Results[0].Name != "content-integrity" {
+		t.Fatalf("expected only the validate phase, got %+v", got.Results)
+	}
+	// A failed preflight step must not leak into the validation verdict.
+	if got.Blocking() {
+		t.Fatal("a failure in another phase must not make validation look failed")
+	}
+}
+
+func TestReportFromStepsOnARunThatNeverValidated(t *testing.T) {
+	rs := &checkpoint.RunState{Steps: []checkpoint.StepRecord{
+		{Phase: checkpoint.PhaseCutover, Name: "start-service", Status: checkpoint.StepDone},
+	}}
+	if got := reportFromSteps(rs); len(got.Results) != 0 {
+		t.Fatalf("expected no results, got %+v", got.Results)
+	}
+}
+
+func TestReportFromStepsKeepsTheError(t *testing.T) {
+	rs := &checkpoint.RunState{Steps: []checkpoint.StepRecord{
+		{Phase: checkpoint.PhaseValidate, Name: "content-integrity", Status: checkpoint.StepFailed, StepOutcome: checkpoint.StepOutcome{Detail: "reached the instance"}, Error: "401 unauthorized"},
+	}}
+	got := reportFromSteps(rs)
+	if d := got.Results[0].Detail; d != "reached the instance (error: 401 unauthorized)" {
+		t.Fatalf("detail = %q, want it to carry both the detail and the error", d)
+	}
+}

cmd/stalwart-migrate/run.go

@@ -21,6 +21,7 @@ import (
 	"github.com/LINUXexpert-org/stalwart-migrator/internal/recovery"
 	"github.com/LINUXexpert-org/stalwart-migrator/internal/service"
 	"github.com/LINUXexpert-org/stalwart-migrator/internal/stage"
+	"github.com/LINUXexpert-org/stalwart-migrator/internal/validate"
 )
 
 // runRun implements `stalwart-migrate run`: the real migration.
@@ -334,6 +335,24 @@ func runRun(args []string) (err error) {
 		return fmt.Errorf("cutover failed: %w", err)
 	}
 
+	fmt.Println("\n--- validate ---")
+	valReport, valErr := validate.RunLive(ctx, store, rs, validate.LiveOptions{
+		AdminURL: *adminURL, AdminUser: *adminUser, AdminPassword: *adminPassword,
+		HTTPClient: httpClient, Before: rs.PreflightSnapshot,
+	})
+	fmt.Print(valReport.String())
+	if valErr != nil {
+		return fmt.Errorf("the migrated service is up, but validation could not complete - check it by hand before "+
+			"treating this migration as done: %w", valErr)
+	}
+	if valReport.Blocking() {
+		// The service is live and serving mail; that is deliberately not
+		// undone here. The operator has the finding and their recovery
+		// point, and only they can weigh one against the other.
+		return fmt.Errorf("the migrated service is up, but accounts or domains from before the migration are missing " +
+			"from it - see the FAIL line above. Your recovery point is the way back; this tool will not undo a migration")
+	}
+
 	fmt.Printf("\nMIGRATION COMPLETE for run %s. Mail was down for %s.\n",
 		rs.RunID, time.Since(windowStart).Round(time.Second))
 	fmt.Printf("Now: confirm you can log in as %s, send and receive a test message, and work through\n", *adminUser)

internal/validate/live.go

@@ -0,0 +1,96 @@
+// SPDX-FileCopyrightText: 2026 LINUXexpert-org
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package validate
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+
+	"github.com/LINUXexpert-org/stalwart-migrator/internal/checkpoint"
+	"github.com/LINUXexpert-org/stalwart-migrator/internal/stalwartapi"
+)
+
+// LiveOptions describes the migrated instance cutover has just started.
+type LiveOptions struct {
+	AdminURL      string
+	AdminUser     string
+	AdminPassword string
+	HTTPClient    *http.Client
+
+	// Before is what preflight captured before anything was touched
+	// (checkpoint.RunState.PreflightSnapshot). Nil when preflight had no
+	// admin URL to capture it from, in which case there is nothing to
+	// compare against and the check reports that rather than passing.
+	Before *checkpoint.PreflightSnapshot
+}
+
+// CheckLive compares a running instance against the pre-migration snapshot.
+//
+// The same comparison BootCheck performs against an instance it booted
+// itself, aimed instead at the service cutover has already started. That is
+// the instance people will actually use — its real config, its real ports,
+// under its real service manager — and checking it costs no extra downtime,
+// where booting a second copy inside the maintenance window would.
+func CheckLive(ctx context.Context, client *stalwartapi.Client, before *checkpoint.PreflightSnapshot) (*ContentIntegrityResult, error) {
+	return compareContentIntegrity(ctx, client, before)
+}
+
+// RunLive executes the post-cutover content comparison as a checkpointed
+// step, mirroring how every other phase records itself.
+//
+// A missing snapshot or admin URL is reported as skipped, never as a pass:
+// "every account survived" and "we were unable to look" are different
+// answers, and ARCHITECTURE.md §4.7 is explicit that this suite must not
+// imply a guarantee it did not measure.
+func RunLive(ctx context.Context, store *checkpoint.Store, rs *checkpoint.RunState, opts LiveOptions) (Report, error) {
+	var report Report
+
+	switch {
+	case opts.AdminURL == "":
+		report.Results = append(report.Results, CheckResult{
+			Name: "content-integrity", Status: StatusSkip,
+			Detail: "no admin URL configured - nothing could be compared against the migrated instance",
+		})
+		return report, nil
+	case opts.Before == nil:
+		report.Results = append(report.Results, CheckResult{
+			Name: "content-integrity", Status: StatusSkip,
+			Detail: "preflight captured no pre-migration snapshot - there is nothing to compare the migrated instance against",
+		})
+		return report, nil
+	}
+
+	client := &stalwartapi.Client{
+		BaseURL: opts.AdminURL, Username: opts.AdminUser, Password: opts.AdminPassword, HTTPClient: opts.HTTPClient,
+	}
+
+	outcome, err := store.RunStep(rs, checkpoint.PhaseValidate, "content-integrity", func() (checkpoint.StepOutcome, error) {
+		r, err := CheckLive(ctx, client, opts.Before)
+		if err != nil {
+			return checkpoint.StepOutcome{}, err
+		}
+		if !r.OK() {
+			// Recorded as a completed step with a failing verdict rather
+			// than an error: the comparison ran, and its answer is the
+			// finding. An error here would read as "we could not look".
+			return checkpoint.StepOutcome{Verdict: string(StatusFail), Detail: r.String()}, nil
+		}
+		return checkpoint.StepOutcome{Detail: r.String()}, nil
+	})
+	if err != nil {
+		report.Results = append(report.Results, CheckResult{
+			Name: "content-integrity", Status: StatusFail,
+			Detail: fmt.Sprintf("could not compare the migrated instance against the pre-migration snapshot: %v", err),
+		})
+		return report, err
+	}
+
+	status := StatusOK
+	if outcome.Verdict == string(StatusFail) {
+		status = StatusFail
+	}
+	report.Results = append(report.Results, CheckResult{Name: "content-integrity", Status: status, Detail: outcome.Detail})
+	return report, nil
+}

internal/validate/live_test.go

@@ -0,0 +1,167 @@
+// SPDX-FileCopyrightText: 2026 LINUXexpert-org
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package validate
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/LINUXexpert-org/stalwart-migrator/internal/checkpoint"
+)
+
+// A run that never captured a "before" cannot be checked against one. The
+// point of these two is that such a run reports as unchecked rather than as
+// passing: ARCHITECTURE.md §4.7 is explicit that this suite must not imply a
+// guarantee it did not measure.
+
+func TestRunLiveSkipsWithoutSnapshot(t *testing.T) {
+	store, rs := newRun(t)
+	report, err := RunLive(context.Background(), store, rs, LiveOptions{AdminURL: "https://mail.example.org", Before: nil})
+	if err != nil {
+		t.Fatalf("RunLive: %v", err)
+	}
+	if got := report.Results[0].Status; got != StatusSkip {
+		t.Fatalf("status = %q, want %q", got, StatusSkip)
+	}
+	if report.Blocking() {
+		t.Fatal("a skipped check must not block the run")
+	}
+	if !strings.Contains(report.Results[0].Detail, "nothing to compare") {
+		t.Fatalf("detail should say why it was skipped, got %q", report.Results[0].Detail)
+	}
+}
+
+func TestRunLiveSkipsWithoutAdminURL(t *testing.T) {
+	store, rs := newRun(t)
+	report, err := RunLive(context.Background(), store, rs, LiveOptions{Before: &checkpoint.PreflightSnapshot{}})
+	if err != nil {
+		t.Fatalf("RunLive: %v", err)
+	}
+	if got := report.Results[0].Status; got != StatusSkip {
+		t.Fatalf("status = %q, want %q", got, StatusSkip)
+	}
+}
+
+func TestRunLivePassesWhenEverythingSurvived(t *testing.T) {
+	srv := fakeInstance(t, []string{"example.org"}, map[string]float64{"[email protected]": 10, "[email protected]": 20})
+	defer srv.Close()
+
+	store, rs := newRun(t)
+	report, err := RunLive(context.Background(), store, rs, LiveOptions{
+		AdminURL: srv.URL, AdminUser: "admin", AdminPassword: "pw", HTTPClient: srv.Client(),
+		Before: &checkpoint.PreflightSnapshot{
+			Domains:   []string{"example.org"},
+			UsedQuota: map[string]int64{"[email protected]": 1, "[email protected]": 2},
+		},
+	})
+	if err != nil {
+		t.Fatalf("RunLive: %v", err)
+	}
+	if report.Blocking() {
+		t.Fatalf("expected a pass, got: %s", report.String())
+	}
+	if got := report.Results[0].Status; got != StatusOK {
+		t.Fatalf("status = %q, want %q", got, StatusOK)
+	}
+}
+
+func TestRunLiveFailsWhenAnAccountIsMissing(t *testing.T) {
+	// bob did not make it across.
+	srv := fakeInstance(t, []string{"example.org"}, map[string]float64{"[email protected]": 10})
+	defer srv.Close()
+
+	store, rs := newRun(t)
+	report, err := RunLive(context.Background(), store, rs, LiveOptions{
+		AdminURL: srv.URL, AdminUser: "admin", AdminPassword: "pw", HTTPClient: srv.Client(),
+		Before: &checkpoint.PreflightSnapshot{
+			Domains:   []string{"example.org"},
+			UsedQuota: map[string]int64{"[email protected]": 1, "[email protected]": 2},
+		},
+	})
+	// The comparison ran and found something: that is a finding, not an
+	// error, so the step completes and the report carries the verdict.
+	if err != nil {
+		t.Fatalf("RunLive returned an error for a completed comparison: %v", err)
+	}
+	if !report.Blocking() {
+		t.Fatalf("a missing account must block, got: %s", report.String())
+	}
+	if !strings.Contains(report.Results[0].Detail, "[email protected]") {
+		t.Fatalf("the report should name the missing account, got %q", report.Results[0].Detail)
+	}
+	// And it must be recorded, so `report <run-id>` can say so afterwards.
+	step := rs.Outcome(checkpoint.PhaseValidate, "content-integrity")
+	if step.Verdict != string(StatusFail) {
+		t.Fatalf("checkpoint verdict = %q, want %q", step.Verdict, StatusFail)
+	}
+}
+
+func TestRunLiveFailsWhenADomainIsMissing(t *testing.T) {
+	srv := fakeInstance(t, []string{"example.org"}, map[string]float64{"[email protected]": 10})
+	defer srv.Close()
+
+	store, rs := newRun(t)
+	report, _ := RunLive(context.Background(), store, rs, LiveOptions{
+		AdminURL: srv.URL, AdminUser: "admin", AdminPassword: "pw", HTTPClient: srv.Client(),
+		Before: &checkpoint.PreflightSnapshot{
+			Domains:   []string{"example.org", "vanished.example"},
+			UsedQuota: map[string]int64{"[email protected]": 1},
+		},
+	})
+	if !report.Blocking() {
+		t.Fatalf("a missing domain must block, got: %s", report.String())
+	}
+	if !strings.Contains(report.Results[0].Detail, "vanished.example") {
+		t.Fatalf("the report should name the missing domain, got %q", report.Results[0].Detail)
+	}
+}
+
+func TestRunLiveFailsWhenTheInstanceCannotBeRead(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusUnauthorized)
+	}))
+	defer srv.Close()
+
+	store, rs := newRun(t)
+	report, err := RunLive(context.Background(), store, rs, LiveOptions{
+		AdminURL: srv.URL, AdminUser: "admin", AdminPassword: "pw", HTTPClient: srv.Client(),
+		Before: &checkpoint.PreflightSnapshot{Domains: []string{"example.org"}},
+	})
+	if err == nil {
+		t.Fatal("expected an error when the instance cannot be read")
+	}
+	if !report.Blocking() {
+		t.Fatalf("being unable to look must not read as a pass, got: %s", report.String())
+	}
+}
+
+func newRun(t *testing.T) (*checkpoint.Store, *checkpoint.RunState) {
+	t.Helper()
+	store := checkpoint.NewStore(t.TempDir())
+	rs, err := store.Create("0.15.5", "0.16.14")
+	if err != nil {
+		t.Fatalf("create run: %v", err)
+	}
+	return store, rs
+}
+
+// fakeInstance answers the principal listing the snapshot is built from.
+func fakeInstance(t *testing.T, domains []string, accounts map[string]float64) *httptest.Server {
+	t.Helper()
+	items := make([]map[string]any, 0, len(domains)+len(accounts))
+	for _, d := range domains {
+		items = append(items, map[string]any{"type": "domain", "name": d})
+	}
+	for name, quota := range accounts {
+		items = append(items, map[string]any{"type": "individual", "name": name, "usedQuota": quota})
+	}
+	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("content-type", "application/json")
+		_ = json.NewEncoder(w).Encode(map[string]any{"data": map[string]any{"items": items, "total": len(items)}})
+	}))
+}

internal/validate/report.go

@@ -13,6 +13,11 @@ type Status string
 const (
 	StatusOK   Status = "ok"
 	StatusFail Status = "fail"
+	// StatusSkip is a check that could not be performed. It is deliberately
+	// not StatusOK: "every account survived" and "we were unable to look"
+	// are different answers, and reporting the second as the first is the
+	// failure mode ARCHITECTURE.md §4.7 warns about.
+	StatusSkip Status = "skip"
 )
 
 type CheckResult struct {