feat(systemd): add robust resume service for sensor re-initialization

[sidneijp]

feat(systemd): add robust resume service for sensor re-initialization

Problem

Fingerprint sensor fails to re-initialize correctly after system suspend/hibernate on modern kernels. The python3-validity service loses its connection to the hardware or enters an inconsistent state, preventing fingerprint authentication upon resume.

Solution

Add a dedicated systemd resume service python3-validity-resume.service that explicitly restarts python3-validity.service and open-fprintd.service when the system wakes up. This ensures a clean state for the driver and the fprintd bridge.

Environment Information

Hardware

• Device: Synaptics, Inc. Metallica MIS Touch Fingerprint Reader
• USB ID: 06cb:009a
• Host System: ThinkPad T480 (Model: <GENERIC_LAPTOP_MODEL>)

Software

• OS: Ubuntu 26.04 LTS (Resolute Raccoon)
• Kernel: 7.0.0-15-generic
• Display Manager: SDDM 0.21.0 (KDE Plasma/Breeze)
• PAM: libpam-modules 1.7.0, libpam-systemd 259.5
• Related Services:
  • open-fprintd (0.7~ppa2)
  • python3-validity (0.15+)

Changes

• Created debian/python3-validity-resume.service to trigger on resume targets.
• Updated debian/rules to ensure proper installation.
• Includes a D-Bus 'readiness gate' via ExecStartPost to ensure the driver is responsive before the service is marked finished.

Steps to Reproduce

1. Complete hardware/firmware setup and enroll fingerprints.
2. Verify initial fingerprint authentication works (e.g., sudo or login).
3. Suspend the system (Sleep/Hibernate).
4. Resume the system.
5. Attempt fingerprint authentication.
   • Observed Behavior (without fix): Sensor is unresponsive or returns USBError [Errno 19]. User is forced to use password fallback.

Validation Steps

1. Install the updated package including python3-validity-resume.service.
2. Suspend the system.
3. Resume the system.
4. Verify the python3-validity-resume.service triggered successfully: systemctl status python3-validity-resume.service.
5. Verify fingerprint authentication works at the login/lock screen.
6. Verify sudo <command> correctly prompts for fingerprint authentication (if enabled in PAM).

Resolves uunicorn#254.