Extend cc-lb with plugins

Plugins extend request routing and payload handling through Wasmtime hooks. The host validates the uploaded module, reads its metadata, checks hook contracts, and binds it into a runtime chain.

Published contract

The published crate set contains five crates:

• cc-lb-plugin-wire
• cc-lb-pdk-wasmtime-macros
• cc-lb-pdk-wasmtime
• cc-lb-runtime-wasmtime
• cc-lb-plugin-conformance

The current plugin contract exposes two slots:

• filter keeps or rejects upstream candidates.
• shape builds the upstream-bound request and transforms buffered and SSE responses.

Start with author a plugin and use conformance before uploading an artifact.