Add experimental local celld runtime adapter #421

Description

This issue proposes an experimental local celld HTTP runtime adapter. Its previous implementation, PR #420, was closed unmerged and marked replaced by #422. Current main has no celld adapter crate. PR #422 delivers native celld stores through Axum, tracked by #437, and explicitly excludes this HTTP runtime scope. Keep the runtime requirement open: no current open PR implements it.

Steps to reproduce

Inspect the status of PR #420 and its replacement comment, then compare #422/#437 with the main workspace adapter list. Local runtime demo results in the closed branch are not a merged adapter.

Expected behavior

An explicitly experimental local adapter runs genuine Rust WASM/workers-rs in celld, advertises its own runtime identity/capabilities and supports registered build/loopback serve and JSON scaffolding. Unsupported remote actions and declared secret stores fail clearly.

Impact

The previous branch contains local demo evidence but is not shipped support. Confusing native stores with a Worker runtime hides the remaining adapter work.

Proposed fix

Reconfirm the local-only runtime design against accepted #275 contracts before resuming implementation. Reuse the Worker transport with explicit runtime/secret/config-reader policy while preserving Cloudflare defaults. Keep generated dependency/ignore rules, bounded verified config envelopes and real generated-consumer/Mocktioneer acceptance. Do not relabel #422 as a runtime adapter or infer fleet/identity guarantees from local demos. AWS deployment, managed secrets, remote config publication and identity Add/CAS remain outside this task.

Done when

• The local adapter design is reconfirmed against accepted portable HTTP/lifecycle contracts.
• Runtime identity/provider metadata, bounded verified config, explicit unsupported behavior and Cloudflare default preservation have focused contracts.
• Generated dependencies/JSON manifests/ignore rules and registered local build/loopback serve work.
• A real generated consumer and Mocktioneer exercise the adapter, with exact revisions/tooling and failure cases recorded.
• Documentation separates local experiment evidence from deployed lifecycle/fleet/performance guarantees.

Related

• Previous implementation: closed, unmerged PR feat(celld): add experimental local Worker runtime adapter #420 and replacement comment.
• Distinct active native-store work: Add native celld configuration and KV store providers #437 / PR Add native celld config and KV store providers #422, on Add native AWS configuration, secret, and ordinary KV store providers #410 / PR Add native AWS store providers #414.
• Prerequisite Implement portable outbound HTTP and request lifecycle contracts #436 / PR feat: implement portable outbound HTTP and request lifecycle contracts #275. Historical companion feat(celld): add local Mocktioneer WASM demo stackpop/mocktioneer#122; Axum readiness Make the Axum adapter production-ready for self-hosted deployments #391 remains separate.