Expose Fastly geo data to replace third-party lookups

[prk-Jr]

Third-party geo and DMA lookups add avoidable latency and introduce additional privacy and compliance risk. This change enables geo information to be derived from Fastly at the edge and passed through the Trusted Server instead of relying on browser-side APIs.

Centralizing geo handling reduces external dependencies, improves reliability when third-party services fail, and supports ongoing efforts to minimize client-side data exposure while preserving existing ad and bidding functionality.

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Technical Implementation

To reliably pass server-side Geo signals to the client-side Prebid auction without race conditions or additional network calls, this PR refactors the Prebid integration to be configuration-driven:

Geo Injection

Decoupled Geo logic into a standalone module:

crates/common/src/geo.rs

• Injects x-geo-* headers
• Exposes a /first-party/geo endpoint

Configuration Injection

Refactored PrebidHtmlInjector:

crates/common/src/integrations/prebid.rs

• Injects the entire Prebid configuration (including resolved Geo data) into:

  window.__tsjs_prebid

Synchronization

Updated the tsjs client library:

crates/js/lib/src/integrations/prebid/index.ts

• Initializes Prebid.js using the injected configuration object
• Ensures the auction always has access to the correct edge-derived location data immediately upon load
• Eliminates asynchronous IP lookups and race-prone client-side fetching

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Resolves: #280