Planting a Future Breaking Change Today: A launchd Timer Job That Deletes Itself When Done

This is a follow-up to my earlier post, " Automating a config migration with a one-shot launchd job ." Some breaking changes come with a known expiration date, and you can prepare for them long before they land. This time the external event was the end-of-life of Fable 5 (2026-07-07), and I'll walk through how I designed a launchd job you set up today, that fires only on the target day, and that removes itself once it's done. The whole thing started with the thought, "manually fixing this on the shutdown day is going to be annoying." But I also didn't want to run a script every morning that needlessly rewrites JSON. What I landed on was a three-part set: a date gate, a jq rewrite with a backup, and self-unload. The problem: on the day I learn about a deprecation, I want to plant a job that "only runs on the target day" Right now, ~/.claude/settings.json looks like this: { "model" : "claude-fable-5[1m]" , ... } The moment I learned Fable 5 would end on 2026-07-07, creating a calendar reminder to manually rewrite this "model" felt too flimsy — I'll forget. On the other hand, making "a daemon that checks the date every time it boots" is overkill. What I wanted was a job I could set once and leave alone, that runs when the day arrives, and then disappears. launchd can fire at a specified time via StartCalendarInterval . But you can't express "just once at 9:00 on 7/7"; you need a combination of recurring and date-fixed slots. Specifying multiple slots and absorbing the redundancy with idempotency is the standard trick on macOS launchd. The implementation: the three-part set Here's the full ~/.claude/scripts/model-transition-0707.sh (comments omitted). #!/bin/bash set -uo pipefail SETTINGS = " $HOME /.claude/settings.json" LOG = " $HOME /.claude/logs/model-transition.log" PLIST = " $HOME /Library/LaunchAgents/com.shun.model-transition-0707.plist" log () { echo "[ $( date '+%F %T' ) ] $* " >> " $LOG " ; } # ① 日付ゲート if [ " $( date +%Y%m%d ) " -lt 20260707 ] ; then log "ski