Brainstorm edge cases for this feature

Before writing tests, to widen the input space you are imagining.

Brainstorm edge cases for the feature below. Be exhaustive first, ranked second.

Work through these lenses:
- Zero, one, many, and far too many.
- Empty, missing, null, whitespace only, maximum length.
- Time: midnight, month end, leap year, daylight saving, clock skew, a user in another timezone.
- Text: non-Latin scripts, right-to-left, emoji, combining characters, case sensitivity.
- Numbers: negative, zero, decimals, currency rounding, overflow.
- People: two actions at once, the same user in two tabs, a user losing permission mid-flow, a deleted account.
- Environment: offline, slow, refreshed mid-action, back button.

Then rank: which cases will occur in production, which are plausible but rare, which are theoretical. Recommend which to test and which to accept.

Feature:

Finding coverage gaps. Working out which behaviours, edge cases and error paths nothing currently checks.