AGENTS.md — Coding Agent Reference

This file is optimized for AI coding agents. It contains hard constraints, ownership rules, and patterns that must not be violated. For human-readable architecture, see architecture.md.

System Overview (30-second version)

Plano is an AI gateway. Client traffic enters Envoy Proxy, passes through two WASM filters (prompt_gateway → llm_gateway), and reaches LLM providers. A native Rust service (Brightstaff) handles intelligent routing and agent orchestration, but always communicates with the outside world through Envoy, never directly.

Hard Rules — Never Violate These

Rule 1: All external I/O goes through Envoy

Brightstaff sends LLM requests to localhost:12001 (Envoy egress listener)
Brightstaff sends agent/API requests to localhost:11000 (Envoy outbound listener)
NEVER add reqwest/hyper calls from Brightstaff directly to external hosts
Routing is controlled by setting x-arch-llm-provider-hint or x-arch-upstream headers

Rule 2: WASM crates cannot use async runtimes

prompt_gateway and llm_gateway compile to wasm32-wasip1
Forbidden in WASM crates: tokio, async-std, reqwest, hyper, std::net, std::fs, std::thread
All I/O uses proxy-wasm SDK's dispatch_http_call (callback-based, not async/await)
governor must use no_std feature; rand is fine

Rule 3: Dependency direction is one-way

prompt_gateway ──► common ──► hermesllm
llm_gateway    ──► common ──► hermesllm
                   llm_gateway ──► hermesllm (direct)
brightstaff    ──► hermesllm (direct, no common WASM code)

hermesllm has zero dependencies on proxy-wasm or common
common has zero dependencies on brightstaff
WASM crates have zero dependencies on brightstaff

Rule 4: Header names are canonical constants

All x-arch-* headers are defined in common/src/consts.rs. Changing a header name requires updating:

common/src/consts.rs
config/envoy.template.yaml
Every Rust consumer (grep for the old constant name)

Rule 5: Config changes require a 4-file update

Adding a new user-facing config field:

config/arch_config_schema.yaml — JSON schema
config/envoy.template.yaml — Jinja2 template (if Envoy needs it)
cli/planoai/config_generator.py — Python validation/rendering
common/src/configuration.rs — Rust struct

Rule 6: API paths are load-bearing

These paths appear in consts.rs, Brightstaff's Axum router, and envoy.template.yaml:

/v1/chat/completions, /v1/messages, /v1/responses
/agents/v1/chat/completions, /agents/v1/messages, /agents/v1/responses
/function_calling, /v1/models, /healthz

Changing them breaks routing. Update all three locations simultaneously.

Rule 7: Reserved model names

Arch-Function — used for intent classification / function calling
Plano-Orchestrator — used for agent selection
Any model prefixed with Arch is treated as internal

Crate Ownership Map

Crate	Type	Target	Owner of
`brightstaff`	Binary (Axum)	Native	LLM routing, agent orchestration, state management, observability
`prompt_gateway`	cdylib (WASM)	wasm32-wasip1	Intent matching, prompt guards, function calling, API orchestration
`llm_gateway`	cdylib (WASM)	wasm32-wasip1	Provider routing, auth injection, rate limiting, request/response translation
`common`	Library	Both	Config types, HTTP client trait, constants, rate limiting, tokenization, shared OpenAI types
`hermesllm`	Library	Native	LLM protocol translation (OpenAI ↔ Anthropic ↔ Bedrock ↔ Gemini), SSE parsing, provider model catalog

Where to Put New Code

You want to...	Put it in...	Why
Add a new LLM provider	`hermesllm` (protocol), `common/configuration.rs` (config type), `config/arch_config_schema.yaml`, `config/envoy.template.yaml` (cluster)	Provider translation is hermesllm's job
Add a new header for inter-component communication	`common/src/consts.rs` + `config/envoy.template.yaml`	Canonical source for all header names
Add rate limiting logic	`common/src/ratelimit.rs`	Shared between WASM filters
Add a new API endpoint to Brightstaff	`brightstaff/src/handlers/` + `brightstaff/src/main.rs` (router)	Axum handler + route registration
Add prompt guardrail logic	`prompt_gateway/src/stream_context.rs` or `prompt_gateway/src/http_context.rs`	Runs inline in Envoy
Add request/response transformation for a provider	`hermesllm/src/transforms/`	Pure Rust, no WASM dependency
Add config validation	`cli/planoai/config_generator.py` + `config/arch_config_schema.yaml`	Python validates before Envoy starts
Add a new metric	`common/src/stats.rs` (WASM) or `brightstaff/src/tracing/` (native)	Different metric systems

Build & Test Quick Reference

# Full build (WASM + native)
cd crates && ./build.sh

# WASM filters only
cargo build --release --target wasm32-wasip1 -p prompt_gateway -p llm_gateway

# Brightstaff only
cargo build --release -p brightstaff

# Run all Rust tests (native)
cargo test --workspace

# Run config generator tests
cd cli && python -m pytest test/

# Dev environment (Docker Compose)
cd config && docker compose -f docker-compose.dev.yaml up

Envoy Listener Map (for routing decisions)

:10000 (ingress)          → passthrough to :10001
:10001 (prompt+llm)       → prompt_gateway.wasm → llm_gateway.wasm → LLM provider
:11000 (outbound API)     → developer APIs & agents (by x-arch-upstream header)
:agent_port (per-config)  → brightstaff :9091 /agents/...
:12000 (LLM egress)       → brightstaff :9091 (routing decision)
:12001 (LLM egress final) → llm_gateway.wasm → LLM provider

Common Mistakes to Avoid

Adding tokio to a WASM crate's Cargo.toml — Will fail to compile for wasm32-wasip1
Making Brightstaff call OpenAI directly — Must go through Envoy at localhost:12001
Adding a config field only in Rust — Schema, Python generator, and template also need updates
Changing a header name in one place — Must grep and update consts.rs, envoy.template.yaml, and all consumers
Adding hermesllm dependency on proxy-wasm — hermesllm must stay pure Rust
Creating a new Envoy cluster without updating the template — Envoy won't know about it
Forgetting no_std feature flag on governor in WASM crates — std governor uses threads

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