Upgrade Pingora after #816 release and remove local proxy patch

Purpose

light-fabric currently patches/vendored pingora-proxy 0.8.1 so a fully consumed, verified request body can be supplied after header-phase authentication and then forwarded through Pingora's normal HTTP/1.1, HTTP/2, body-filter, and retry paths.

Upstream Cloudflare Pingora PR #816 is expected to provide the equivalent supported lifecycle. The light-fabric integration requirement and intended migration path are recorded in this PR #816 comment.

Application-managed buffering regression coverage was contributed in CodyPubNub/pingora PR #1. That test leaves automatic early buffering disabled, consumes the body in request_filter(), calls Session::set_buffered_body(), verifies normal request_body_filter() execution and exact upstream bytes, and forces a retry to prove replay works.

Current local patch

• Workspace override: Cargo.toml [patch.crates-io] pingora-proxy = { path = "patches/pingora-proxy" }
• Vendored crate: patches/pingora-proxy/
• Local callback: ProxyHttp::prebuffered_request_body
• Consumers:
  • apps/hmac-phase0-spikes/src/main.rs
  • apps/light-gateway/src/main.rs
• Background: patches/pingora-proxy/README.light-fabric.md

Do not remove this patch merely because #816 merges. Wait for an official Pingora release that contains the required behavior, and confirm the application-managed set_buffered_body() contract and regression remain present in that release.

Upgrade and removal checklist

• Confirm Cloudflare Pingora PR #816 is merged and identify the first official Pingora release containing it.
• Confirm the released implementation supports the light-fabric ordering: header policy/rate limiting first, bounded application body capture and HMAC/replay processing in request_filter(), then Session::set_buffered_body().
• Confirm application-supplied bodies traverse normal request_body_filter(), HTTP/1.1 and HTTP/2 forwarding, and retry replay. Use the contributed regression as the minimum contract.
• Upgrade all Pingora dependencies together to the selected release and update Cargo.lock.
• Enable the upstream Cargo feature/API required for early or application-managed body buffering without opting into automatic pre-request_filter() buffering.
• Replace both prebuffered_request_body consumers with the released upstream API while preserving HMAC ordering, per-profile body timeout, exact-body verification, aggregate buffer accounting, and fail-closed behavior.
• Remove the root [patch.crates-io] override and delete patches/pingora-proxy/ only after the upstream implementation passes all gates.
• Verify rg 'prebuffered_request_body|patches/pingora-proxy' has no unintended runtime references.
• Run the cumulative HMAC gate: ./scripts/run-hmac-phase4-gates.sh (this includes phases 0 through 3, light-pingora, light-gateway, clippy, docs, cross-runtime fixtures, live Redis, formatting, and git diff --check).
• Re-run any upstream Pingora regression supplied by the selected release, including the application-managed buffering/retry case.
• Update the HMAC design/operations documentation and close this issue with the Pingora version, upstream commit/release, removed patch paths, and gate evidence.

Acceptance criteria

• No local pingora-proxy crate override or vendored patch remains.
• Standalone and Unified Security HMAC flows retain their current ordering and exact-body behavior.
• Application-managed buffered bodies work for HTTP/1.1, HTTP/2, normal body filters, and upstream retries.
• ./scripts/run-hmac-phase4-gates.sh passes against the released upstream Pingora dependency.

First confirm the Pingora release containing Cloudflare PR #816 and compare its buffering and retry behavior with the regression described in CodyPubNub/pingora PR #1. Review Cargo.toml, patches/pingora-proxy/, apps/hmac-phase0-spikes/src/main.rs, and apps/light-gateway/src/main.rs, then update dependencies and remove the patch while preserving the documented HMAC ordering and buffering contract. Run ./scripts/run-hmac-phase4-gates.sh and verify no unintended references remain.