Model To Header Trust Existing

# AI Inference Model Routing: Trust an Existing Model Header
#
# Routes on a model header that a trusted hop in front of Praxis has
# already set, skipping the filter entirely when the header is present.
# The `unless: {headers_present: ["X-AI-Model"]}` condition keeps the
# incoming header as is. A request without one still has the body's
# "model" field promoted into X-AI-Model by the filter, as usual.
#
# Security: this turns off the anti-spoofing strip when the header is
# present, so whoever sends the header picks the backend. Only use it
# when every request reaches Praxis through a hop that sets or scrubs
# the header.
#
# Usage:
#   cargo run -p praxis-ai-proxy -- -c examples/configs/model-to-header-trust-existing.yaml
#
#   # Routed by the header to the granite cluster; the filter is skipped.
#   curl -X POST http://localhost:8080/v1/chat/completions \
#     -H "Content-Type: application/json" \
#     -H "X-AI-Model: granite-3.1-8b" \
#     -d '{"model": "granite-3.1-8b", "messages": []}'
#
#   # No header: the body's model is promoted and routes to mistral.
#   curl -X POST http://localhost:8080/v1/chat/completions \
#     -H "Content-Type: application/json" \
#     -d '{"model": "mistral-7b-instruct", "messages": []}'

listeners:
  - name: inference-gateway
    address: "127.0.0.1:8080"
    filter_chains:
      - extract-model
      - routing

filter_chains:
  # Skip the filter when X-AI-Model is already present from a trusted
  # hop; otherwise promote the body's "model" field into it.
  - name: extract-model
    filters:
      - filter: model_to_header
        conditions:
          - unless:
              headers_present: ["X-AI-Model"]
        header: X-AI-Model

  # Route based on X-AI-Model, wherever it came from.
  - name: routing
    filters:
      - filter: router
        routes:
          - path_prefix: "/"
            headers:
              x-ai-model: "mistral-7b-instruct"
            cluster: mistral
          - path_prefix: "/"
            headers:
              x-ai-model: "granite-3.1-8b"
            cluster: granite
          - path_prefix: "/"
            cluster: default
      - filter: load_balancer
        clusters:
          - name: mistral
            endpoints:
              - "127.0.0.1:3000"
          - name: granite
            endpoints:
              - "127.0.0.1:3001"
          - name: default
            endpoints:
              - "127.0.0.1:3002"

insecure_options:
  allow_private_endpoints: true # example proxies to local backends