Document fix for 'Failed to connect to bus' when setting up Umami systemd user service

Co-authored-by: Junie <junie@jetbrains.com>

aidlc-docs/features/react-frontend/audit.md

@@ -624,3 +624,15 @@
 **Context**: Post-workflow follow-up (feature already marked Complete); continues the `feature/analytics_uptime_dashboard` branch, resolving a connectivity blocker discovered while the user was testing the Umami container on Pi Main. Documentation-only change (no code/build impact); the actual `ufw allow` command still needs to be run by the user on Pi Main.
 
 ---
+
+## Post-Completion Follow-up: "Failed to connect to bus: No medium found" When Setting Up the systemd User Service
+
+**Timestamp**: 2026-07-25T23:18:00Z
+
+**User Input**: "ik krijg het volgende al sik de service probeer aan te maken en deamon reload probeer te doen: systemctl --user daemon-reload Failed to connect to bus: No medium found"
+
+**AI Response**: "Explained that this error means no D-Bus/systemd user session exists yet for the `umami` user, most likely because `sudo -iu umami` does not register a full PAM login session the way an interactive login does — so `/run/user/<uid>` (and the bus socket inside it) is missing, even with linger already enabled. Added a troubleshooting callout to `umami-setup.md` right before the systemd-service step: verify `Linger=yes` via `loginctl show-user umami`, re-run `loginctl enable-linger umami` if not, explicitly start `user@<uid>.service`, re-login and export `XDG_RUNTIME_DIR` manually, with `machinectl shell umami@ /bin/bash` offered as a more robust alternative to `sudo -iu`/`su -` if the issue persists."
+
+**Context**: Post-workflow follow-up (feature already marked Complete); continues the `feature/analytics_uptime_dashboard` branch, resolving a blocker discovered while the user was setting up the systemd auto-start service on Pi Main. Documentation-only change (no code/build impact); the user still needs to apply the fix on Pi Main.
+
+---

aidlc-docs/features/react-frontend/operations/monitoring/umami-setup.md

@@ -124,6 +124,28 @@ uit stap 0.3 is hiervoor al gezet, dus deze service blijft ook draaien zonder da
 `umami`-user zelf is ingelogd.
 
 1. Log in (of blijf ingelogd) als de `umami`-user: `sudo -iu umami`.
+
+> **Let op — "Failed to connect to bus: No medium found" bij `systemctl --user`:**
+> Dit betekent dat er (nog) geen D-Bus/systemd user-sessie draait voor `umami`, meestal
+> omdat `sudo -iu umami` geen volledige PAM-login-sessie registreert zoals een echte
+> interactieve login dat wel doet — daardoor bestaat `/run/user/<uid>` (en de bus daarin)
+> nog niet, zelfs met linger enabled. Los dit als volgt op:
+> ```bash
+> # Controleer eerst of linger daadwerkelijk actief staat:
+> loginctl show-user umami | grep Linger
+> # Verwacht: Linger=yes. Staat er Linger=no, herhaal dan:
+> sudo loginctl enable-linger umami
+> # Start de user-manager expliciet (uid van umami opzoeken met: id -u umami):
+> sudo systemctl start user@$(id -u umami).service
+> # Log opnieuw in als umami en zet XDG_RUNTIME_DIR expliciet, voor deze sessie:
+> sudo -iu umami
+> export XDG_RUNTIME_DIR=/run/user/$(id -u)
+> ```
+> Probeer daarna `systemctl --user daemon-reload` opnieuw. Blijft het misgaan, gebruik dan
+> in plaats van `sudo -iu umami` het commando `sudo machinectl shell umami@ /bin/bash` om
+> in te loggen — dat registreert wél altijd een volledige sessie inclusief D-Bus, in
+> tegenstelling tot `sudo -iu`/`su -`.
+
 2. Maak `~/.config/systemd/user/umami.service` aan:
    ```ini
    [Unit]