SignalSalad Architecture

Architecture and C4 model documentation.

C4 Graphs At A Glance

View	Purpose
Level 1 - System Context	External actors + system boundary
Level 2 - Container View	Runtime containers + protocol edges
Deployment View	Local/cloud placement model
Level 3 - Signaling	Control-plane routing and orchestration
Level 3 - Ingress	Ingress media control + relay source
Level 3 - Egress	Egress relay termination + fanout
Level 3 - Webapp	Browser session/media orchestration
Message Sequences	End-to-end request/callback stories

Level 1 - System Context: who uses SignalSalad and what does it do?
Level 2 - Container View: What are the runtime containers and protocols between them?
Deployment View: What will this look like deployed on the cloud?
Scaling: How do the media servers scale?
Level 3 - Signaling Code View: How does signaling work?
Level 3 - Ingress Code View: How do the ingress media servers work?
Level 3 - Egress Code View: How do the egress media servers work?
Level 3 - Webapp Code View: How does the demo webapp work?
Message Sequences: step-by-step request/callback stories.
Core Terms: shared architecture terms and naming conventions.

Concern	Primary Owner	Supporting Owner(s)	Main Docs
User session actions	SPA Client + Signaling Service	Ingress/Egress Media	Level 2, Signaling L3, Webapp L3
Client transport setup (WebRTC)	SPA Client	Ingress/Egress Media	Webapp L3, Ingress/Egress L3
Room/peer lifecycle	Signaling Service	SPA Client	Signaling L3, Message Sequences
Media relay orchestration	Signaling Service + Media Services	-	Signaling L3, Ingress/Egress L3

SPA Client: Browser app (webapp) that drives user session/media actions.
Signaling Service: Control-plane service that routes requests and coordinates room/peer/media-server state.
Ingress Media Service: Media node that receives upstream media from clients.
Egress Media Service: Media node that sends downstream media to clients.
NetworkPipeRelay: Ingress-to-egress relay path between media services.

Signaling Facade: Listener-facing entrypoint in signaling.ts.
Runtime Topology: Composition root in signalingRuntimeTopology.ts.
Transport Wrappers: Transport-specific request ingress handling (websocketIngressFlow.ts, netsocketSignalFlow.ts).
Flow Modules: Request/callback routing modules (signaling/lib/signaling/flows/*).
Protocol Contracts: Typed message builders + validators (signaling/lib/protocol/*).

WebSocket: Client <-> signaling control channel (/signaling, /status).
Netsocket: Signaling <-> media control channel (TCP).
Request Router: Switch-style dispatch by message type.
Typed Error Response: Protocol-level error payload with explicit message type/shape.