In addition to the mess caused by Canadian time zone changes in the latest TZDB & CLDR, another change in TZDB 2026d has impact on JS: EST5EDT, CST6CDT, MST7MDT, PST8PDT are now canonical IDs (called primary time zone identifiers in 262 & 402) again.

This means that these zones may start showing up in Intl-powered UI time zone pickers, which seems bad. If we want CLDR revert this change then we've gotta act fast. See https://github.com/tc39/ecma402/issues/1103 for context.

cc sffc