fix: strip double quotes from sftp.args flags to prevent restic parse error

internal/api/backresthandler.go

@@ -990,7 +990,16 @@ func (s *BackrestHandler) GeneratePairingToken(ctx context.Context, req *connect
 func sanitizeRepoFlags(repo *v1.Repo) {
 	for i, flag := range repo.Flags {
 		if strings.HasPrefix(flag, "--option=sftp.args=") {
-			repo.Flags[i] = strings.ReplaceAll(flag, "-i @", "-i ")
+			// Remove the "-i @" workaround since we now handle quoting properly
+			flag = strings.ReplaceAll(flag, "-i @", "-i ")
+			// Strip double quotes from sftp.args values that cause restic's
+			// pflag parser to fail with "bare \" in non-quoted-field".
+			// The UI wraps paths in double quotes (e.g. -i "/path/to/key"),
+			// but restic's --option flag parser cannot handle them.
+			// Paths passed as sftp.args don't need quoting since they are
+			// passed directly to sftp as individual arguments.
+			flag = strings.ReplaceAll(flag, "\"", "")
+			repo.Flags[i] = flag
 		}
 	}
 }

internal/api/backresthandler_test.go

@@ -1123,3 +1123,52 @@ func getOperations(t *testing.T, log *oplog.OpLog) []*v1.Operation {
 	}
 	return operations
 }
+
+func TestSanitizeRepoFlags(t *testing.T) {
+	tests := []struct {
+		name  string
+		flags []string
+		want  []string
+	}{
+		{
+			name:  "strip double quotes from sftp.args",
+			flags: []string{`--option=sftp.args='-oBatchMode=yes -i "/root/.ssh/id_ed25519" -p 23 -oUserKnownHostsFile="/root/.ssh/known_hosts"'`},
+			want:  []string{`--option=sftp.args='-oBatchMode=yes -i /root/.ssh/id_ed25519 -p 23 -oUserKnownHostsFile=/root/.ssh/known_hosts'`},
+		},
+		{
+			name:  "strip double quotes with -i @ workaround",
+			flags: []string{`--option=sftp.args='-oBatchMode=yes -i @/root/.ssh/id_ed25519"'`},
+			want:  []string{`--option=sftp.args='-oBatchMode=yes -i /root/.ssh/id_ed25519'`},
+		},
+		{
+			name:  "no sftp.args flags unchanged",
+			flags: []string{`--option=some.other=value`},
+			want:  []string{`--option=some.other=value`},
+		},
+		{
+			name:  "sftp.args without double quotes unchanged",
+			flags: []string{`--option=sftp.args=-oBatchMode=yes`},
+			want:  []string{`--option=sftp.args=-oBatchMode=yes`},
+		},
+		{
+			name:  "mixed flags only sftp.args modified",
+			flags: []string{`--option=other=val`, `--option=sftp.args='-i "/path/key"'`},
+			want:  []string{`--option=other=val`, `--option=sftp.args=-i /path/key`},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			repo := &v1.Repo{Flags: tt.flags}
+			sanitizeRepoFlags(repo)
+			if len(repo.Flags) != len(tt.want) {
+				t.Fatalf("got %d flags, want %d", len(repo.Flags), len(tt.want))
+			}
+			for i, got := range repo.Flags {
+				if got != tt.want[i] {
+					t.Errorf("flags[%d] = %q, want %q", i, got, tt.want[i])
+				}
+			}
+		})
+	}
+}