feat(llm-d): move ext_proc compatibility into AI

[nerdalert]

Summary

Moves the llm-d ext_proc compatibility layer into the AI repository under integrations/llmd/ext-proc/.

This replaces the abandoned Praxis-side crate publication approach. See the comments from @shaneutt in praxis-proxy/praxis#780 for details. I am pushing a draft as I need it for llm-d integration work in grid so this may be temporary if Shane has other plans for gating ext_proc exposure.

The crate is AI-owned, publish = false, and scoped to llm-d’s current EPP protocol rather than general-purpose Envoy ext_proc support.

Runtime registration is gated behind the praxis-ai-proxy/llmd-ext-proc feature. Default praxis-ai-proxy builds do not link, register, or expose the ext_proc filter.

What changed

• Added praxis-ai-llmd-ext-proc at integrations/llmd/ext-proc/
• Added llmd-ext-proc feature to praxis-ai-proxy
• Added six llm-d environment tests using llm-d-inference-sim
• Added docs for the support boundary and test flow
• Temporarily pinned Praxis to 546871d8fdb85a6b0260e77ee4a63083c1c097fb until the next Praxis release includes required support APIs
• Allowed the pinned Praxis git source in deny.toml

Why draft

Opening this as a draft because the ownership and support boundary should be reviewed before treating this as final.

The main points needing maintainer review are:

• whether integrations/llmd/ext-proc/ is the right long-term location for the llm-d-only compatibility layer
• whether the llmd-ext-proc feature boundary is strict enough
• whether the public wording is clear that this is not general-purpose Envoy ext_proc support

Dependency pin

This branch temporarily pins the Praxis crates to:

546871d8fdb85a6b0260e77ee4a63083c1c097fb

The current published 0.4.0 Praxis crates do not include APIs used by this transfer, including:

• TrustedHeaderMutation
• pre_read_mutations
• set_structured_metadata
• MetricsConfig

The intent is not to keep a git dependency permanently. Once Praxis publishes a release containing those APIs, this should move back to normal released crate dependencies.

Known caveats

• cargo deny check currently exits 2 because of pre-existing duplicate-version bans on AI main. The branch-specific Praxis git source allowance passes under sources ok.

• The COPY examples ./examples container fix is included here so the draft branch can build images. It may be dropped during rebase if the standalone container fix lands first in fix(container): restore container image builds #333.

• The Praxis git pin is temporary and should be replaced by released Praxis crate versions once the required APIs are published.

  Validation

  • cargo check --workspace
  • cargo check --features praxis-ai-proxy/llmd-ext-proc
  • cargo clippy --workspace --all-targets -- -D warnings
  • cargo clippy --workspace --all-targets --features praxis-ai-proxy/llmd-ext-proc -- -D warnings
  • cargo test --workspace --exclude praxis-tests-environment
  • cargo test -p praxis-tests-environment --features llmd-ext-proc -- --test-threads=1
  • RUSTDOCFLAGS="-D warnings" cargo doc --workspace --no-deps --document-private-items
  • make container
  • git diff --check