Did a Fourth-century Council Actually Order People Not to Rest on Shabbath?

Council: Laodicea (4th c.) · Evidence: Canon 29

What the ancient record says

Yes. Canon 29 says Christianoi must not "Judaize" by resting on the Shabbath, and gives the opposite instruction, they must work on that day, telling them to honor the "Lord's Day" and, if possible, rest then.

It contrasts the days: Shabbath, do not rest, work; the other day, honor it, and if possible rest. Those found "Judaizing" were to be anathema from Christ (the precise institutional effect studied in its canonical context; the condemnation is explicit).

Does not prove nobody observed Shabbath after Laodicea, a prohibition can show the opposite: authorities do not normally prohibit what nobody does; at minimum Shabbath-rest observance remained significant enough to be formally addressed (how widespread needs separate evidence). Did Laodicea "change the Shabbath" by itself?

Too simple, Sunday observance existed before Laodicea, Shabbath observance also continued; the development occurred over time. What Laodicea gives: a formal canon telling Christianoi not to rest on Shabbath and to work instead.