Initial scoping: architecture + Asterisk→Rust port plan

Establish rutster — a memory-safe, API-first, security-first telephony
platform; spiritual successor to Asterisk for the WebRTC/microservices era.

- README: project framing, design pillars, open decisions
- docs/ARCHITECTURE.md: three-plane (control/media/app) model
- docs/PORT_PLAN.md: every Asterisk subsystem mapped to a disposition
  (core / WASM-plugin / service / edge-FFI / dropped / replaced) with rationale

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01C2bfD7MkqEdfnMXxXBu456

README.md

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+# Rutster
+
+A memory-safe, API-first, security-first telephony platform — a spiritual successor
+to Asterisk for the WebRTC/microservices era, written in Rust.
+
+> Not a port of Asterisk. A reimagining that keeps the *power* — era-bridging breadth,
+> "wire anything to anything," a deep feature library — while dropping the legacy
+> hardware/dead-protocol half and fixing Asterisk's two chronic wounds:
+> memory-safety CVEs and toll fraud, at the design level.
+
+## What it is / isn't
+
+- **Is:** SIP (TLS-only) + WebRTC signaling, a real-time media plane (transcode / mix /
+  DSP), a programmable call model exposed as a REST/gRPC API + event stream, a
+  WASM-sandboxed plugin runtime, and a library of telephony features delivered as
+  isolated services.
+- **Isn't:** A TDM/PSTN-hardware PBX. No DAHDI, no Sangoma/Digium cards, no ISDN/SS7,
+  no IAX2/H.323/SCCP/MGCP/Unistim. PSTN reach is via SIP trunks / SBC only.
+
+## Core design pillars
+
+1. **Memory-safe by construction** — Rust everywhere on the hot path; fuzzed, sans-IO
+   protocol parsers. Eliminates the buffer-overflow/RCE CVE class.
+2. **Isolation over in-process modules** — extensions run in a **WASM sandbox**, not as
+   `.so` files in the daemon's address space. One bad plugin can't crash the box or
+   read another tenant's media. (The Asterisk `core show locks` era ends here.)
+3. **Secure & deny-by-default** — mandatory TLS/SRTP, deny-by-default routing,
+   built-in toll-fraud controls, mTLS gRPC admin (no plaintext AMI), hard multi-tenancy.
+4. **Three planes, scaled independently** — control / media / app. The media datapath
+   stays tight; business logic is microservices and plugins around it.
+5. **Observable & declarative** — OpenTelemetry call traces across services;
+   config-as-data, not imperative `.conf` files edited on a box.
+
+## Layout
+
+- [`docs/ARCHITECTURE.md`](docs/ARCHITECTURE.md) — the three-plane model and pillars.
+- [`docs/PORT_PLAN.md`](docs/PORT_PLAN.md) — **the spine**: every Asterisk subsystem mapped
+  to a disposition (core / plugin / service / edge-FFI / dropped) with rationale.
+
+## Status
+
+Scoping. No code yet — the port plan defines the crate/service boundaries that the
+workspace will be scaffolded from next.
+
+## Open decisions
+
+- **License** — undecided (Asterisk is GPLv2+commercial; rutster's model is TBD).
+- **SIP stack** — FFI to pjproject vs. front with an SBC (Kamailio/drachtio) vs. a
+  long-term pure-Rust stack. See port plan §1.
+- **WASM runtime** — `wasmtime` is the presumptive default (component model).