@remotion/studio: Request element install targets on demand

[JonnyBurger]

Summary

• Stop polling /api/update-element-install-target from Studio
• Let /api/element-install-target request the current target from connected Studio clients over EventSource
• Have Studio clients POST the target only in response to that request
• Keep target replies request-scoped so concurrent probes do not reuse stale target data

Testing

• bun test packages/studio-server/src/test/element-install-state.test.ts
• bun run --cwd packages/studio-shared make
• bun run --cwd packages/studio-server make
• bun run --cwd packages/studio make
• bun run build
• bun run stylecheck
• bun run --cwd packages/studio formatting
• bun run --cwd packages/studio make

Closes #9023

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Project	Deployment	Actions	Updated (UTC)
bugs	Ready	Preview, Comment	Jul 11, 2026 2:29pm
remotion	Ready	Preview, Comment	Jul 11, 2026 2:29pm

[pullfrog]

✅ No new issues found.

Reviewed changes — the change replaces the fixed 2-second polling of /api/update-element-install-target with a change-only dispatch, and extends the server-side install-target max age from 5 seconds to 5 minutes to match the focused-window TTL.

• packages/studio/src/components/Canvas.tsx — adds areElementInstallTargetsEqual and a lastSentElementInstallTargetRef so the API request is only issued when the payload actually changes; focus and pointerdown events trigger re-evaluation, and failed requests reset the ref so the next change resends.
• packages/studio-server/src/preview-server/element-install-state.ts — raises ELEMENT_INSTALL_TARGET_MAX_AGE to 5 * 60 * 1000 so the server-state TTL aligns with the focus-based TTL used in packages/studio-server/src/routes.ts.

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