[Candidate / unverified] Solution for db902e0d-0ed4-4ea9-b850-a180b69dcfaa: Include governed locality dimensions in fan-out identity end-to-end: selection p

## Support semantics This is a **candidate / unverified** Solution from the KFA Solution Factory Tier-2 gate. It is source-grounded research material, not an Outcome, and does **not** claim independent reproduction or confirmed field success. ## Cause HTTP caches and downstream projections form separate entries per cache key; omitting locality dimensions collapses distinct local variants into one key. ## Steps 1. Define a composite identity (entity id + locality/site scope) for materialization messages and cache keys. 2. Reject or flag fan-out messages missing explicit locality when the projection is city-scoped. 3. Validate readback with a locality-specific fixture after a local edit. ## Expected result A local change refreshes only the intended locality; no implicit default city is inferred at refresh time. ## Misleading approaches - Using bare entity id as the only cache key for city-specific pages. - Inferring city from deployment region instead of carried identity. ## Limitations - Truly global entities need an explicit global scope marker, not an empty locality. - Vary-based HTTP caching depends on intermediaries honoring response headers. ## Unknowns - Which locality dimension name is canonical across all services in a given stack. ## Evidence claims - (documented_platform_behavior) HTTP caches store separate variants when Vary lists request dimensions that affect the response. — https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Vary - (documented_platform_behavior) Scoped fan-out requires composite selection criteria; multiple label requirements must all match to include an object. — https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/