Prototype portable KV-backed Geo lookup - #454

Summary

• Restack the existing standalone KV Geo prototype above the refreshed Add pluggable native Geo providers and protected CloudFront ingress #439 branch. Preserve the original importer, lookup algorithm, harness, manifest and historical measurement documents.
• Reconcile only the prototype lockfile with the current Core dependencies. No production crate, Geo dispatch or asynchronous production provider is added.
• Keep this PR draft. CloudFront remains the demo's serving provider; this prototype is not production KV Geo.

Stack and exact inputs

Base: #439, feature/pluggable-geo-providers at 22741b615d9369772830e64da92893207ac37b27.

Head: c155e5de3438b75bc81668ec8de2b6feabb2100a.

The delta is the original nine prototype/document paths. Runtime source bytes remain identical to the original e4ede101 experiment. The Core source tree used by the earlier passing restack is also identical. #453 is excluded, with no MaxMind implementation merged.

Refs #438 and #391. This experiment does not close their production acceptance work.

Checks

Fresh checks on this restack:

• cargo test --offline --locked --manifest-path examples/geo-kv-prototype/Cargo.toml: 10 passed, zero ignored.
• Prototype all-target Clippy with -D warnings.
• Prototype formatting and whitespace checks.

Reusable earlier proof has unchanged prototype/lock/Core inputs: release build, workspace exclusion and Core dependency isolation, plus synthetic CLI repeat-build, 768 cache/oracle comparisons and eight fresh lookups. Historical real-data measurements remain attached to their original source and measurement record; they were not rerun for this restack.

No current combined-workspace or hosted runtime pass is claimed by these prototype checks. The standalone crate remains excluded from the root workspace, so ordinary workspace CI does not exercise it automatically.

Limits

The harness stores artifacts through synchronous local files behind KvHandle. This does not establish remote KV publication, latency, propagation, cancellation, reader-IP provenance, request integration, deployed cache behavior or fleet durability. Country-code compatibility and format/publication decisions remain as documented in the unchanged design and results files.

No licensed dataset, generated index, credentials or deployment inputs are added. No deployment or live infrastructure change is part of this PR.