Upstream 6.10.9 does indeed seem to fix it. Half a dozen runs of my reproducers yielded nothing but correct behavior.
Bug#1079394: linux-image-6.10.6-amd64: causes cifs regression, flatpak & ostree signature corruption
- Bug#1079394: linux-image-6.10.6-amd64: causes cifs re... Salvatore Bonaccorso
- Bug#1079394: linux-image-6.10.6-amd64: causes ci... Forest
- Bug#1079394: linux-image-6.10.6-amd64: cause... Forest