fix(demo): preload the Cal.com booking embed while the visitor fills the form

[waleedlatif1]

Summary

• The demo page's Cal.com calendar took several seconds to appear after submitting the booking form: nothing embed-related (embed.js, the booker iframe, its assets) started downloading until the visitor pressed Continue
• Warm the entire path on first form focus using the embed's documented preload instruction — it caches the booker's assets in a hidden ?preload=true iframe while the visitor fills the form
• Add a preconnect to app.cal.com (React 19 react-dom API) so the first embed request skips connection setup
• Zero Cal.com traffic at initial page load, so Lighthouse/LCP are untouched; verified with Playwright — the calendar now finishes loading ~815ms after submit instead of starting cold

Type of Change

• Bug fix

Testing

Tested manually with Playwright against the running app: confirmed no cal.com requests on page load, preload iframe attaches ~200ms after first form focus, and the booker renders fully ~815ms after submit

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		Jul 12, 2026 2:47am

[cursor]

PR Summary

Low Risk
Landing demo UX only; lazy-loading and no Cal.com requests on first paint are preserved, with limited surface area.

Overview
Fixes slow Cal.com calendar appearance after demo form submit by warming the booking path on first form focus instead of only lazy-loading the scheduler chunk.

DemoBooking now calls preloadScheduler() on onFocusCapture, which uses React 19 preconnect('https://app.cal.com'), dynamically imports the scheduler module, and invokes new preloadCalEmbed(). That helper loads Cal.com embed.js and runs the embed API’s preload instruction (hidden booker iframe) with idempotent guards and retry on failed script load. Initial page load still avoids Cal.com traffic; embed work overlaps form fill time.

^{Reviewed by Cursor Bugbot for commit 9e49846. Configure here.}

[greptile-apps]

Greptile Summary

This PR preloads the Cal.com demo scheduler after the visitor starts the form.

• Moves the Cal.com preconnect into the focus-triggered preload path.
• Loads the scheduler chunk before the booking step is shown.
• Adds a preloadCalEmbed helper for the Cal.com embed preload instruction.
• Re-exports the scheduler preload helper from the scheduler barrel.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
apps/sim/app/(landing)/demo/components/demo-booking/demo-booking.tsx	Moves the Cal.com preconnect into preloadScheduler, which runs from the existing form focus preload path.
apps/sim/app/(landing)/demo/components/demo-scheduler/demo-scheduler.tsx	Adds preloadCalEmbed to load the Cal.com embed API and issue the scheduler preload instruction.
apps/sim/app/(landing)/demo/components/demo-scheduler/index.ts	Exports preloadCalEmbed alongside DemoScheduler for the lazy preload path.

_{Reviews (2): Last reviewed commit: "fix(demo): retry embed warm-up on failur..." | Re-trigger Greptile}

[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

[cursor]

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^{Reviewed by Cursor Bugbot for commit 9e49846. Configure here.}