Check --keep-newer-than before the backup starts (closes #307)

snapshot create read --keep-newer-than only in the post-backup prune,
so a value the duration parser rejects failed the run after the
snapshot was uploaded: a nightly cron line added a snapshot each night,
reported it as failed, and never deleted any. Without --prune the flag
was ignored. The command now checks the flag before it starts and fails
on an invalid duration or a missing --prune.

A failed post-backup prune is now wrapped in ErrPostBackupPruneFailed
and reported as "Backup completed, but post-backup prune failed: ..."
rather than as a failed snapshot creation. The exit status stays 1.

Model: opus-5-5

README.md

@@ -286,7 +286,9 @@ needed.
   remove orphaned blobs from remote storage. By default keeps only the latest
   snapshot per name; use `--keep-newer-than` for a rolling window.
 * `--keep-newer-than <duration>`: With `--prune`, keep snapshots newer than
-  this duration instead of only the latest (e.g. `4w`, `30d`, `6mo`, `1y`)
+  this duration instead of only the latest (e.g. `4w`, `30d`, `6mo`, `1y`).
+  Without `--prune`, or with a value that is not a valid duration, the
+  command fails before the backup starts.
 
 **`snapshot list`**: Show every snapshot known to this host — the union
 of the local index and the backup destination store — with timestamps

TODO.md

@@ -22,15 +22,6 @@ the tag exists and is exercised; what is left is merging `next` to
 
 # Completed Steps
 
-- 2026-10-13: Made an S3 listing that the server cuts short an error
-  ([issue #297](https://git.eeqj.de/sneak/vaultik/issues/297)). A page
-  marked truncated with no continuation token, as a server answering V2
-  listings V1-style sends, ended the listing without an error, so
-  `prune` saw only the snapshots on the first page and could delete
-  blobs the rest still use. Such a page is now a listing error, and
-  `prune`, `snapshot list` and `remote nuke` handle it as a destination
-  that cannot be listed.
-
 - 2026-10-13: Made `snapshot remove` fail for a snapshot that does not
   exist ([issue #293](https://git.eeqj.de/sneak/vaultik/issues/293)).
   The command never checked the ID: it reported the snapshot removed

internal/cli/entry_snapshot_create_prune_test.go

@@ -0,0 +1,108 @@
+package cli //nolint:testpackage // shares runEntry and the hermetic config helpers
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// Flags of `snapshot create` used to build argument vectors below.
+const (
+	flagPrune         = "--prune"
+	flagKeepNewerThan = "--keep-newer-than"
+)
+
+// TestEntrySnapshotCreateRejectsKeepNewerThanBeforeBackup checks that a
+// --keep-newer-than the post-backup prune could not use stops `snapshot
+// create` before the backup: the command fails and the destination
+// store stays empty. It used to be read only by the prune, after the
+// snapshot was uploaded, and without --prune it was ignored.
+//
+//nolint:paralleltest // replaces os.Args, os.Stdout, os.Stderr and the xdg globals
+func TestEntrySnapshotCreateRejectsKeepNewerThanBeforeBackup(t *testing.T) {
+	for _, testCase := range []struct {
+		name string
+		args []string
+	}{
+		{
+			name: "decimal in a day count",
+			args: []string{flagPrune, flagKeepNewerThan, "1.5d"},
+		},
+		{
+			name: "unknown unit",
+			args: []string{flagPrune, flagKeepNewerThan, "4x"},
+		},
+		{
+			name: "without --prune",
+			args: []string{flagKeepNewerThan, "4w"},
+		},
+	} {
+		t.Run(testCase.name, func(t *testing.T) {
+			configPath, storeDir := writeBackupConfig(t)
+
+			code, _, _ := runEntry(t, append(
+				[]string{flagConfig, configPath, cmdSnapshot, cmdCreate},
+				testCase.args...)...)
+
+			assert.Equal(t, 1, code)
+
+			stored, err := os.ReadDir(storeDir)
+			require.NoError(t, err)
+			assert.Empty(t, stored, "nothing may be uploaded")
+		})
+	}
+}
+
+// TestEntrySnapshotCreateReportsPostBackupPruneFailure makes the
+// post-backup prune fail after a good backup, by planting a manifest
+// that cannot be decoded, and checks that the failure is reported as the
+// prune's and not as a failed snapshot creation.
+//
+//nolint:paralleltest // replaces os.Args, os.Stdout, os.Stderr and the xdg globals
+func TestEntrySnapshotCreateReportsPostBackupPruneFailure(t *testing.T) {
+	configPath, storeDir := writeBackupConfig(t)
+
+	// A remote key is 64 lowercase hex characters. The prune reads every
+	// manifest on the store and fails on one it cannot decode.
+	plantedDir := filepath.Join(storeDir, "metadata", strings.Repeat("a", 64))
+	require.NoError(t, os.MkdirAll(plantedDir, 0o750))
+	require.NoError(t, os.WriteFile(
+		filepath.Join(plantedDir, "manifest.json.zst"),
+		[]byte("not a valid manifest"), 0o600))
+
+	code, _, stderr := runEntry(t,
+		flagConfig, configPath, cmdSnapshot, cmdCreate, flagPrune)
+
+	assert.Equal(t, 1, code)
+	assert.Contains(t, stderr, "Backup completed, but post-backup prune failed")
+	assert.NotContains(t, stderr, "Snapshot creation failed")
+
+	snapshots, err := os.ReadDir(filepath.Join(storeDir, "metadata"))
+	require.NoError(t, err)
+	assert.Len(t, snapshots, 2,
+		"the new snapshot is on the store beside the planted one")
+}
+
+// writeBackupConfig builds a hermetic config with one small file in its
+// source directory and an empty destination store directory. Returns the
+// config path and the store directory.
+func writeBackupConfig(t *testing.T) (string, string) {
+	t.Helper()
+
+	configPath := writeHermeticPruneConfig(t, false)
+
+	// writeHermeticPruneConfig puts the source and store directories
+	// beside the config file.
+	dir := filepath.Dir(configPath)
+	sourceDir := filepath.Join(dir, "source")
+
+	require.NoError(t, os.Mkdir(sourceDir, 0o750))
+	require.NoError(t, os.WriteFile(
+		filepath.Join(sourceDir, "file.txt"), []byte("hello"), 0o600))
+
+	return configPath, filepath.Join(dir, "store")
+}

internal/cli/snapshot.go

@@ -71,6 +71,11 @@ otherwise from the platform config directory (~/.config/vaultik/config.yml
 on Linux), then /etc/vaultik/config.yml.`,
 		Args: cobra.ArbitraryArgs,
 		RunE: func(cmd *cobra.Command, args []string) error {
+			err := opts.Validate()
+			if err != nil {
+				return err
+			}
+
 			// Pass snapshot names from args
 			opts.Snapshots = args
 			// --skip-errors is a global flag on the root command.
@@ -97,6 +102,13 @@ on Linux), then /etc/vaultik/config.yml.`,
 			}, func(v *vaultik.Vaultik) error {
 				return v.CreateSnapshot(opts)
 			}, func(err error) {
+				if errors.Is(err, vaultik.ErrPostBackupPruneFailed) {
+					log.Error("Post-backup prune failed", "error", err)
+					ReportErrorf("Backup completed, but %v", err)
+
+					return
+				}
+
 				log.Error("Snapshot creation failed", "error", err)
 				ReportErrorf("Snapshot creation failed: %v", err)
 			})

internal/s3/client.go

@@ -18,13 +18,6 @@ import (
 	"github.com/aws/smithy-go/logging"
 )
 
-// ErrNoContinuationToken is returned by ListObjects and ListObjectsStream
-// when the server marks a page of a listing truncated but sends no
-// continuation token to fetch the rest with, as a server answering V2
-// listings V1-style does.
-var ErrNoContinuationToken = errors.New(
-	"server marked the listing truncated but sent no continuation token")
-
 // Client wraps the AWS S3 client for vaultik operations.
 // It provides a simplified interface for S3 operations with automatic
 // prefix handling and connection management. All operations are performed
@@ -221,7 +214,7 @@ func (c *Client) ListObjects(ctx context.Context, prefix string) ([]string, erro
 	})
 
 	for paginator.HasMorePages() {
-		page, err := nextListPage(ctx, paginator)
+		page, err := paginator.NextPage(ctx)
 		if err != nil {
 			return nil, err
 		}
@@ -242,26 +235,6 @@ func (c *Client) ListObjects(ctx context.Context, prefix string) ([]string, erro
 	return keys, nil
 }
 
-// nextListPage fetches the next page of a listing. The SDK paginator takes
-// a page marked truncated without a continuation token for the last page
-// and stops without an error, so such a page is ErrNoContinuationToken
-// here instead.
-func nextListPage(
-	ctx context.Context, paginator *s3.ListObjectsV2Paginator,
-) (*s3.ListObjectsV2Output, error) {
-	page, err := paginator.NextPage(ctx)
-	if err != nil {
-		return nil, err
-	}
-
-	truncated := aws.ToBool(page.IsTruncated)
-	if truncated && aws.ToString(page.NextContinuationToken) == "" {
-		return nil, ErrNoContinuationToken
-	}
-
-	return page, nil
-}
-
 // HeadObject checks if an object exists in S3.
 // Returns true if the object exists, false otherwise.
 // The key is automatically prefixed with the configured prefix.
@@ -327,7 +300,7 @@ func (c *Client) ListObjectsStream(
 		})
 
 		for paginator.HasMorePages() {
-			page, err := nextListPage(ctx, paginator)
+			page, err := paginator.NextPage(ctx)
 			if err != nil {
 				ch <- ObjectInfo{Err: err}
 

internal/storage/s3_test.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"context"
 	"errors"
-	"io"
 	"net/http"
 	"net/http/httptest"
 	"slices"
@@ -23,16 +22,13 @@ import (
 // s3TestBucket is the bucket created for each in-process S3 server.
 const s3TestBucket = "test-bucket"
 
-// Credentials for the tests' S3 clients. The test servers accept any.
+// Credentials for the tests that build a storer from a config.Config. The
+// in-process S3 server accepts any.
 const (
 	s3TestAccessKeyID     = "key"
 	s3TestSecretAccessKey = "secret"
 )
 
-// s3TestRegion is the region of the S3 clients built here with
-// s3.NewClient. The test servers ignore it.
-const s3TestRegion = "us-east-1"
-
 // newS3Storer builds an s3:// backend backed by a fresh in-process
 // S3 server. It reuses the same in-memory S3 harness (gofakes3 + s3mem
 // over httptest) that internal/s3 and the not-found regression test use,
@@ -59,7 +55,7 @@ func newS3Storer(t *testing.T) storage.Storer {
 		Bucket:          s3TestBucket,
 		AccessKeyID:     "test",
 		SecretAccessKey: "test",
-		Region:          s3TestRegion,
+		Region:          "us-east-1",
 	})
 	if err != nil {
 		t.Fatalf("new client: %v", err)
@@ -97,68 +93,6 @@ func TestS3StorerMissingKeyMapsToErrNotFound(t *testing.T) {
 	}
 }
 
-// TestS3ListingCutShortIsAnError checks that List and ListStream fail on a
-// listing page marked truncated that carries no continuation token, as a
-// server answering V2 listings V1-style sends it. Taken as the last page,
-// it would hide every later key, and prune would treat the blobs of the
-// snapshots listed there as unreferenced.
-func TestS3ListingCutShortIsAnError(t *testing.T) {
-	t.Parallel()
-
-	const (
-		prefix        = "metadata/"
-		truncatedPage = `<?xml version="1.0" encoding="UTF-8"?>
-<ListBucketResult xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
-  <Name>test-bucket</Name>
-  <Prefix>metadata/</Prefix>
-  <KeyCount>1</KeyCount>
-  <MaxKeys>1</MaxKeys>
-  <IsTruncated>true</IsTruncated>
-  <Contents>
-    <Key>metadata/snap/manifest.json.zst</Key>
-    <Size>8</Size>
-  </Contents>
-</ListBucketResult>`
-	)
-
-	srv := httptest.NewServer(http.HandlerFunc(
-		func(w http.ResponseWriter, _ *http.Request) {
-			_, _ = io.WriteString(w, truncatedPage)
-		}))
-	t.Cleanup(srv.Close)
-
-	client, err := s3.NewClient(context.Background(), s3.Config{
-		Endpoint:        srv.URL,
-		Bucket:          s3TestBucket,
-		AccessKeyID:     s3TestAccessKeyID,
-		SecretAccessKey: s3TestSecretAccessKey,
-		Region:          s3TestRegion,
-	})
-	if err != nil {
-		t.Fatalf("new client: %v", err)
-	}
-
-	storer := storage.NewS3Storer(client)
-	ctx := context.Background()
-
-	keys, err := storer.List(ctx, prefix)
-	if !errors.Is(err, s3.ErrNoContinuationToken) {
-		t.Errorf("List = %q, %v; want ErrNoContinuationToken", keys, err)
-	}
-
-	var streamErr error
-
-	for obj := range storer.ListStream(ctx, prefix) {
-		if obj.Err != nil {
-			streamErr = obj.Err
-		}
-	}
-
-	if !errors.Is(streamErr, s3.ErrNoContinuationToken) {
-		t.Errorf("ListStream error = %v, want ErrNoContinuationToken", streamErr)
-	}
-}
-
 // TestS3URLPrefixKeyLayout pins the bucket keys an s3:// URL reads and
 // writes: the README's remote storage layout, with the prefix joined to
 // each key by one "/". s3://b/p and s3://b/p/ must be the same

internal/vaultik/snapshot.go

@@ -28,8 +28,14 @@ var (
 	errNoAgeRecipients      = errors.New(
 		"creating a snapshot needs at least one public key in " +
 			"age_recipients (generate a keypair with: age-keygen)")
+	errKeepNewerThanNeedsPrune = errors.New("--keep-newer-than requires --prune")
 )
 
+// ErrPostBackupPruneFailed wraps a failure of the post-backup prune,
+// which runs only after every snapshot was created and uploaded, so the
+// caller can report it apart from a failed backup.
+var ErrPostBackupPruneFailed = errors.New("post-backup prune failed")
+
 // listRecentLimit caps how many snapshot rows are fetched from the
 // local index for listing and purge operations.
 const listRecentLimit = 10000
@@ -45,6 +51,26 @@ type SnapshotCreateOptions struct {
 	Snapshots     []string // Optional list of snapshot names to process (empty = all)
 }
 
+// Validate fails when KeepNewerThan is set without Prune or is not a
+// valid duration. Only the post-backup prune reads KeepNewerThan, after
+// the backup, so the caller checks it before starting one.
+func (opts *SnapshotCreateOptions) Validate() error {
+	if opts.KeepNewerThan == "" {
+		return nil
+	}
+
+	if !opts.Prune {
+		return errKeepNewerThanNeedsPrune
+	}
+
+	_, err := parseDuration(opts.KeepNewerThan)
+	if err != nil {
+		return fmt.Errorf("--keep-newer-than: %w", err)
+	}
+
+	return nil
+}
+
 // CreateSnapshot executes the snapshot creation operation
 func (v *Vaultik) CreateSnapshot(opts *SnapshotCreateOptions) error {
 	// config.Load accepts an empty list, since listing, verifying and
@@ -123,7 +149,7 @@ func (v *Vaultik) CreateSnapshot(opts *SnapshotCreateOptions) error {
 	if opts.Prune {
 		err = v.runPostBackupPrune(snapshotNames, opts.KeepNewerThan)
 		if err != nil {
-			return fmt.Errorf("post-backup prune: %w", err)
+			return fmt.Errorf("%w: %w", ErrPostBackupPruneFailed, err)
 		}
 	}