What problems was I solving

Page rendering needed live execution support for custom components with per-instance isolation, comprehensive diagnostics, and runtime asset resolution.

What user-facing changes did I ship

Custom component images can now be resolved from asset-ids at runtime rather than requiring pre-resolved URLs. Custom components render in sandboxed iframes with runtime height auto-adaptation and visibility diagnostics.

How I implemented it

Implemented iframe-based custom component runtime (page-ui) with strict CSP sandboxing, postMessage protocol for height/diagnostics, and auto-detection of parent origin from referrer. Wire custom component service throughout page gateway execution pipeline (rendering model → session data → state stream) for bidirectional asset-URL resolution.

Description for the changelog

Adds custom component runtime support with sandboxed iframe execution and automatic asset URL resolution. Upgrades scheduler dependency to 0.26.0 for React suspense/blocking compatibility. Introduces preview messaging utilities for diagnostics and selection in preview mode. Maintains per-instance isolation and strict security constraints (sandbox, CSP, origin verification).