From b2222fb33838a86ecf593d5d17add570066db972 Mon Sep 17 00:00:00 2001
From: Cal Corum <calcorum@users.noreply.github.com>
Date: Fri, 20 Feb 2026 00:47:13 -0600
Subject: [PATCH] store: Systemd OnCalendar=weekly and OnCalendar=daily fire
 simultaneously on Sundays/Mondays - always stagger shared-state timers

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+---
+id: b33e2316-6313-4ed9-b95a-3a469b820101
+type: insight
+title: "Systemd OnCalendar=weekly and OnCalendar=daily fire simultaneously on Sundays/Mondays - always stagger shared-state timers"
+tags: [systemd, timer, gotcha, race-condition, cognitive-memory, scheduling]
+importance: 0.5
+confidence: 0.8
+created: "2026-02-20T06:47:13.739265+00:00"
+updated: "2026-02-20T06:47:13.739265+00:00"
+---
+
+# Systemd Timer Collision Gotcha
+
+## The Problem
+`OnCalendar=weekly` resolves to `Mon *-*-* 00:00:00` (Monday midnight). If another timer uses `OnCalendar=daily`, both fire at the same second on Monday midnight. Any two services that share a state file will race each other.
+
+## Consequence
+Silent data loss. If both services do read-modify-write on the same JSON file without atomic locking, one will clobber the other's changes. If the loser's write also corrupts the file, a silent `JSONDecodeError` catch can return an empty dict, permanently losing all state.
+
+## Fix Pattern
+Always stagger timers that access shared resources by at least an hour:
+
+```ini
+# Instead of:
+OnCalendar=weekly
+
+# Use:
+OnCalendar=Sun *-*-* 02:00:00
+```
+
+This avoids the Monday midnight collision and gives the daily timer time to finish first.
+
+## General Rule
+Never schedule two services that share state files at the same `OnCalendar` interval without explicit offset staggering.