Originally published on hexisteme notes .

At 21:00 on October 9, and again at 09:00 the next morning, the snapshot job in my agent telemetry pipeline raised this alert:

F3-SOURCE-CHECK-ERROR: argument --since: not an ISO-8601 timestamp: '1970-01-01T00:00:00Z'

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The alert's wording pointed at suspected loss of the raw archive. Nothing had been lost. The archive copy was working, and its newest file was from 08:59 that morning. What failed was a source-freshness check inside the same job. The parse error was the easy part; what it had been covering up was the real lesson.

Python 3.9 and a trailing Z

Under cron's PATH, python3 resolved to /usr/bin/python3 , which is 3.9.6. Before 3.11, datetime.fromisoformat does not accept a trailing Z , and the job passes --since 1970-01-01T00:00:00Z . My interactive shell runs 3.13, so nothing reproduced by hand.…