* fix(mobile): keep source-control layout steady while Create PR eligibility loads
The Create PR entry unmounted until the first hostedReview.getCreationEligibility
answer arrived, so on a cold open the changed-files list painted first and then
shifted down 54pt (createPrBlock marginTop 12 + createPrButton minHeight 42)
when the button appeared — while the user was already tapping (#8411).
- buildMobileCreatePrAction: cold loading now reserves the row with a disabled
placeholder instead of unmounting it.
- useMobileHostedReviewEligibility: a fetch-imminent idle frame renders as an
in-flight load, so the reservation is present on the first painted frame.
- New per-worktree+branch memory of the last resolved eligibility seeds cold
loads, so branches whose answer is hidden (existing review, unsupported
provider) do not get a placeholder that collapses on every reopen.
Fixes#8411
* fix(mobile): harden source-control layout reservation
* fix(mobile): keep review status row footprint fixed
* fix(mobile): derive eligibility state from keyed snapshots
Brennan Benson