…/date-time

…class on initial entry (ionic-team#31108)
Issue number: internal
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## What is the current behavior?
`ion-datetime` runs two IntersectionObservers: one to detect when the
host becomes visible (which adds `datetime-ready`) and one to detect
when it becomes hidden (which removes the class and tears down
listeners). When the host mounts offscreen, both observers receive an
initial "not intersecting" entry on `observe()`. The hidden-state
observer treats that initial entry as a real visible-to-hidden
transition, queues a `writeTask` to remove `datetime-ready`, and races
the layout-based fallback (`ensureReadyIfVisible`) that adds the class
after 100ms. On WebKit the remove wins often enough that the e2e test
for the fallback (added in ionic-team#30793 to fix ionic-team#30706) had to be skipped on
Mobile Safari. Anything in production that adds `datetime-ready` outside
of a real `isIntersecting: true` event is exposed to the same race.
## What is the new behavior?
A `hasBeenIntersecting` flag is set true only when `visibleCallback`
observes `isIntersecting: true`. The hidden-state observer's teardown is
gated on this flag, so the synthetic initial "not intersecting" entry is
ignored. The flag is reset when the host actually transitions to hidden
and on `disconnectedCallback`. The previously duplicated init-listeners
+ ready-class block is consolidated into a single `markReady` helper.
The WebKit skip on the IO-fallback e2e test has been removed.
## Does this introduce a breaking change?
- [ ] Yes
- [x] No
<!-- If yes, please describe the impact and migration path for existing
applications below. -->
## Other information
The asymmetry where `ensureReadyIfVisible` (the layout fallback)
deliberately does NOT set `hasBeenIntersecting` is load-bearing: the
flag must reflect a real observer signal, not a fallback-driven write,
otherwise the bug returns. This is called out at the guard site so
future cleanups don't undo it.
This test was most likely to fail in docker testing Linux Webkit with
`--repeat-each=20` because it was pretty flaky. I was able to force it
to fail under these conditions and, after fixing it, it no longer
failed.
## Relevant Preview Link:
-
https://ionic-framework-git-fw-7284-ionic1.vercel.app/src/components/datetime/test/basic