Run: python3 -I test.py on 2026-10-23
PASS sample is UTF-8 and CRLF terminated
PASS sample header equals the 7 spec columns ['date', 'weekday', 'platform', 'pillar', 'format', 'status', 'notes']
PASS sample has 32 rows (32)
PASS every row has 7 non-empty fields
PASS weekday matches date on every row
PASS dates span 2026-11-02 to 2026-11-29 (4 weeks)
PASS no pillar repeats back to back on one platform (repeats: 0)
PASS pillar mix is even (counts differ by at most 2) {'Plant care how-tos': 9, 'Behind the shop': 8, 'Customer shelves': 8, 'New arrivals and offers': 7}
PASS same-day same-pillar clashes across platforms
PASS status values limited to Idea/Drafted/Scheduled/Posted
PASS notes unique
PASS blank template: header + 28 dated rows, 7 columns
PASS blank template: dates are 28 consecutive days from 2026-11-02
PASS blank template: platform, pillar, format, notes empty

Source reads, 2026-10-23, headless Chromium (Playwright) on the VPS, body text searched for the rule:
https://help.instagram.com/439971288310029/?hl=en -> "You must have a public account on Instagram. You can schedule up to 25 posts a day, up to 30 days in advance."
https://ads.tiktok.com/business/en-US/blog/introducing-video-scheduler-now-you-can-plan-tiktoks-in-advance -> "schedule videos anywhere from 15 minutes to 10 days in advance of publishing. You'll need a Business Account" (no update date on the page)
https://help.pinterest.com/en/business/article/schedule-pins -> "You can schedule a Pin up to 30 days in advance ... you can have up to 10 Pins scheduled for the future."
https://www.linkedin.com/help/linkedin/answer/a1347212 -> "You can schedule a post between 10 minutes and 3 months from the current time."
https://www.linkedin.com/help/linkedin/answer/a1419179 -> "anywhere between an hour from the current time to three months in advance" (Last updated: 11 months ago)
https://support.google.com/youtube/answer/1270709 -> scheduling steps read; no maximum window stated in the page text
https://help.x.com/en/using-x/scheduling-posts and facebook.com help guesses: not read (timeout or no relevant text)
Hootsuite page (curl + sed + grep): "Most teams plan their social media calendar one to four weeks in advance, with larger campaigns mapped out months ahead."
Sprout Social page: no text on planning horizon found; Buffer page: one quoted creator plans three months ahead.