correct backup tag key, metadata not found (#1830)

## Description

Fixes two bugs: 1. building the correc tag key
when retrieving the prior backup id from a
manifest.  2. returning ErrNotFound when a
snapshot entry isn't found for restore.  This
can occur for metadata if the service has
a prior backup that does not contain the
expected metadata files.

## Does this PR need a docs update or release note?

- [x] ⛔ No 

## Type of change

- [x] 🐛 Bugfix

## Issue(s)

* #1823

## Test Plan

- [x] 💪 Manual

src/cli/backup/onedrive.go

@@ -334,7 +334,7 @@ func oneDriveDetailsCmd() *cobra.Command {
 	}
 }
 
-// lists the history of backup operations
+// prints the item details for a given backup
 func detailsOneDriveCmd(cmd *cobra.Command, args []string) error {
 	ctx := cmd.Context()
 

src/internal/kopia/wrapper.go

@@ -2,6 +2,7 @@ package kopia
 
 import (
 	"context"
+	"strings"
 
 	"github.com/hashicorp/go-multierror"
 	"github.com/kopia/kopia/fs"
@@ -277,6 +278,10 @@ func getItemStream(
 		encodeElements(itemPath.PopFront().Elements()...),
 	)
 	if err != nil {
+		if strings.Contains(err.Error(), "entry not found") {
+			err = errors.Wrap(ErrNotFound, err.Error())
+		}
+
 		return nil, errors.Wrap(err, "getting nested object handle")
 	}
 

src/internal/operations/backup.go

@@ -211,26 +211,19 @@ func produceManifestsAndMetadata(
 			continue
 		}
 
-		bup := backup.Backup{}
+		k, _ := kopia.MakeTagKV(kopia.TagBackupID)
+		bupID := man.Tags[k]
 
-		if err := sw.Get(
-			ctx,
-			model.BackupSchema,
-			model.StableID(man.Tags[kopia.TagBackupID]),
-			&bup,
-		); err != nil {
+		bup, err := sw.GetBackup(ctx, model.StableID(bupID))
+		if err != nil {
 			return nil, nil, err
 		}
 
 		colls, err := collectMetadata(ctx, kw, graph.MetadataFileNames(), oc, tid, bup.SnapshotID)
-		if err != nil {
+		if err != nil && !errors.Is(err, kopia.ErrNotFound) {
 			// prior metadata isn't guaranteed to exist.
 			// if it doesn't, we'll just have to do a
 			// full backup for that data.
-			if errors.Is(err, errNotRestored) {
-				continue
-			}
-
 			return nil, nil, err
 		}
 
@@ -240,8 +233,6 @@ func produceManifestsAndMetadata(
 	return ms, collections, err
 }
 
-var errNotRestored = errors.New("unable to restore metadata")
-
 func collectMetadata(
 	ctx context.Context,
 	kw *kopia.Wrapper,