Recover from half-done installs and missing devices instead of failing for good

- pi_shairport: on trixie systemd.pc moved into systemd-dev, so configure found no
  unit directory and `make install` died on an empty `install -d` - after it had
  already installed the binary. `creates:` then saw the binary and never retried, and
  the next tasks failed on the missing unit. Install systemd-dev on trixie, and key
  `creates:` on the unit file.
- pi_irserver: with the IRTrans receiver unplugged at boot, irserver exited at once and
  stayed failed. Restart it every 10s with no start limit until the device shows up.
- pi_modern_shell_env: get_url sent a conditional request to the oh-my-posh CDN on every
  run, so a TLS handshake timeout there failed the whole play with the binary already
  installed. Only download it when it is missing.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

roles/pi_irserver/files/irserver.service

@@ -1,10 +1,17 @@
 [Unit]
 Description=IR server for IR remotes
 After=network.target
+# Keep retrying rather than giving up: the IRTrans receiver is a USB serial device, and
+# when it is missing at boot (unplugged, or enumerated late) irserver exits at once with
+# "Error opening COM/USB Port". Without a restart it then stays failed until someone
+# notices the remote does nothing.
+StartLimitIntervalSec=0
 
 [Service]
 Type=simple
 ExecStart=/usr/bin/irserver /dev/ttyUSB0
+Restart=on-failure
+RestartSec=10
 
 [Install]
 WantedBy=multi-user.target

roles/pi_modern_shell_env/tasks/main.yml

@@ -17,7 +17,17 @@
     dest: /usr/local/bin/bat
     state: link
 
+- name: Check whether oh-my-posh is already installed
+  ansible.builtin.stat:
+    path: /usr/local/bin/oh-my-posh
+  register: pi_modern_shell_env_ohmyposh
+
 - name: Download oh-my-posh binary
+  # Only when missing. With the file present get_url still sends a conditional request
+  # every run, so a CDN that is slow or unreachable from the device (TLS handshake
+  # timeouts happen) failed the whole play for a prompt that was already installed.
+  # Delete the binary to pick up a newer release.
+  when: not pi_modern_shell_env_ohmyposh.stat.exists
   ansible.builtin.get_url:
     # The official install script's own curl-based downloads are blocked by
     # oh-my-posh's CDN on some devices (observed on Raspberry Pi OS's curl

roles/pi_shairport/tasks/main.yml

@@ -3,24 +3,20 @@
   ansible.builtin.apt:
     cache_valid_time: 7200
     state: present
-    name:
-      - build-essential
-      - git
-      - xmltoman
-      - autoconf
-      - automake
-      - libtool
-      - libpopt-dev
-      - libconfig-dev
-      - libasound2-dev
-      - avahi-daemon
-      - libavahi-client-dev
-      - libssl-dev
-      - libsoxr-dev
+    # systemd-dev: --with-systemd takes the unit directory from systemd.pc, which trixie
+    # moved out of the systemd package. Without it `make install` fails right after
+    # installing the binary, with an empty `install -d`.
+    name: >-
+      {{ ['build-essential', 'git', 'xmltoman', 'autoconf', 'automake', 'libtool',
+          'libpopt-dev', 'libconfig-dev', 'libasound2-dev', 'avahi-daemon',
+          'libavahi-client-dev', 'libssl-dev', 'libsoxr-dev']
+         + (['systemd-dev'] if ansible_facts.distribution_major_version | int >= 13 else []) }}
 - name: Build and Install Shairport sync (may take a while)
   ansible.builtin.script: "build-shairport-sync.sh ${shairport_sync_version}"
   args:
-    creates: /usr/local/bin/shairport-sync
+    # The unit file rather than the binary: make install puts the binary in place
+    # first, so a build that failed halfway would otherwise never be retried.
+    creates: /lib/systemd/system/shairport-sync.service
   notify: Restart shairport-sync
 - name: Copy config
   ansible.builtin.template: