Hybrid AEMaaCS + Edge Delivery Services (EDS) — Fastly CDN routing, shared header/nav, and AEM servlet consumption from EDS

We're building a hybrid implementation where a handful of pages (e.g., Home, Contact Us) are served via Edge Delivery Services (EDS), while the remainder of the site continues to run on AEM as a Cloud Service (AEMaaCS). Looking for guidance/best practices from the community on the following:

1. Splitting traffic between EDS and AEMaaCS via Fastly
Since AEMaaCS ships with a managed Fastly CDN in front of it, for a hybrid site where only select pages are served from EDS and the rest from AEMaaCS:

• Should the path-based routing rules (to send specific URLs to EDS vs AEMaaCS origin) be configured in the AEMaaCS Cloud Manager / Fastly  on the AEM side, or should they live in the EDS project's ?
• Since AEMaaCS Fastly config is managed through Cloud Manager pipelines, is there a supported way to add custom routing rules there ?
• Any guidance on keeping this maintainable as more pages incrementally migrate to EDS over time?

2. Sharing a common header/navigation (XF) between AEMaaCS and EDS pages
Our global navigation is built as an Experience Fragment (XF) rendered in AEMaaCS. When a nav entry should point to a page now hosted on EDS:

• Is manually maintaining an AEM path → EDS URL mapping the standard/only approach today?
• Or is there a way to resolve this dynamically via Sling Model logic (e.g., a resource resolution/link rewriting mechanism that detects EDS-migrated pages) instead of a hardcoded list?
• Has anyone implemented a shared header pattern (single source of truth for nav, consumed by both AEMaaCS and EDS) — e.g., using an EDS block that fetches nav data, or exposing AEM nav via a JSON model endpoint consumed by EDS?

3. Consuming AEMaaCS servlets from EDS pages

For EDS pages that need to invoke AEMaaCS servlets/endpoints (e.g., forms, dynamic data lookups):

• What's the recommended way to handle CORS between the EDS domain and the AEMaaCS publish tier (given AEMaaCS's managed dispatcher)?
• Are there specific dispatcher / CDN header configurations (in the AEMaaCS dispatcher project) needed to safely expose these endpoints to EDS, and any Adobe-recommended security considerations (auth tokens, allow-listing origins, etc.)?

Any official documentation, reference architectures, or war stories from teams who've done this hybrid AEMaaCS + EDS rollout would be greatly appreciated.

Thank you very much.