myevent:<token>#<YYYY-MM-DD>. The token says which recurring thing, the
local day says which time round, and marks, ignores, progress and daily
ticks all key off the whole string — so an occurrence carries its own
completion and its own streak rather than sharing the rule's.
'#' is outside [a-z0-9] and therefore outside CustomEventId, so an
occurrence cannot be written back into the store or survive an import.
That is the guardrail rather than a code path anybody has to remember, and
a test pins it in both directions.
Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
