[scheduler] Unify `EventSkeleton` and `ErrorContainer` between `EventCalendar` and `EventTimeline`

[rita-codes]

Follow-up from #22308.

The EventCalendar/EventCalendarPremium and EventTimelinePremium duplicate EventSkeleton and ErrorContainer. Both pairs are flagged with cross-referenced TODO #22309 comments in the source.

Current state

ErrorContainer — structurally identical

• packages/x-scheduler/src/internals/components/error-container/ErrorContainer.tsx
• packages/x-scheduler-premium/src/event-timeline-premium/error-container/EventTimelinePremiumErrorContainer.tsx

Both versions are structurally identical. The only differences left are:

• The store context hook (useEventCalendarStoreContext vs useEventTimelinePremiumStoreContext)
• The styled context hook (useEventCalendarStyledContext vs useEventTimelinePremiumStyledContext)
• The styled() name field (MuiEventCalendar vs MuiEventTimeline)

EventSkeleton — diverges in sizing

• packages/x-scheduler/src/internals/components/event-skeleton/EventSkeleton.tsx
• packages/x-scheduler-premium/src/event-timeline-premium/content/event-skeleton/EventTimelinePremiumSkeleton.tsx

The calendar version takes a required data-variant: 'time-column' | 'day-grid' | 'agenda' prop and applies different layout per variant (absolute positioning vs fixed heights). The timeline version has no variant — single theme-derived height + width: 100%.

Proposed approach

Create two shared components in packages/x-scheduler/src/internals/components/ with their own theme namespaces (following the MuiEventDialog precedent for shared scheduler components):

EventSkeleton

• New theme name: MuiEventSkeleton.
• Add a fourth variant 'timeline-row' (theme-derived height + width: 100%) so the timeline can consume the same component.
• Both products use the shared component with the appropriate variant.
• Delete EventTimelinePremiumSkeleton.tsx.

ErrorContainer

• New theme name: MuiEventErrorContainer.
• Pass the store as a prop (or via a small product-agnostic hook) so the shared component is decoupled from a specific store context.
• Both products use it.
• Delete EventTimelinePremiumErrorContainer.tsx.

Each product can keep a thin wrapper if it needs to inject the store/classes from its own styled context, but the styled root + JSX lives in the shared component.

What to clean up

• The four TODO #22309 comments in the source files linked above.
• The duplicated component files in packages/x-scheduler-premium/src/event-timeline-premium/.
• Any imports/exports referencing the removed components.

Notes for the implementer

• The scheduler is in alpha, so introducing new theme namespaces is acceptable.
• Existing consumers using theme.components.MuiEventCalendar.styleOverrides.eventSkeleton (or the MuiEventTimeline equivalent) will lose their override after the rename — document this as a breaking change in the PR description.

[Baisayan]

can u assign this to me? give more details

[rita-codes]

Hey! Thanks for offering @Baisayan 🙂

This one is a follow-up of an ongoing PR I still have open, so I’m going to keep it on hold for now until that lands.

Once it’s unblocked I can share more details and we can see if it still makes sense for you to pick it up! 🙌

[Baisayan]

sure just mention me, as soon as its unblocked. would love to help

[rita-codes]

Updated the description and removed the on hold label.
The proposed approach + cleanup checklist are in the description above.

Thanks for picking this up @Baisayan, happy to help if anything's unclear! 🙌

[github-actions]

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