feat: InternalConnection generalization

[ggfevans]

Parent Epic

Part of #362 (Connection Graph Model - Port-Based Architecture)

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Summary

Add InternalConnection to DeviceType to model internal topology (PDU circuits, patch panel pass-through, switch fabric, chassis backplane).

Background

Devices like PDUs have internal topology - an input feeds multiple outlets through circuits. Patch panels have pass-through connections from front to rear. This internal topology enables power path traversal and connection tracing.

Type Definition

type InternalConnectionType = 
  | 'power-distribution'   // PDU inlet → outlets
  | 'passthrough'          // Patch panel front ↔ rear
  | 'fabric'               // Chassis backplane
  | 'stacking';            // Switch stack ring

interface InternalConnection {
  from_interface: string;      // InterfaceTemplate.name
  to_interfaces: string[];     // Array of InterfaceTemplate.name
  connection_type: InternalConnectionType;
  circuit_name?: string;       // For PDU circuits: "Bank A"
  breaker_amps?: number;       // For PDU circuits: 20
}

Acceptance Criteria

• Create InternalConnection interface
• Create InternalConnectionType enum
• Add internal_connections: InternalConnection[] to DeviceType
• Validate that referenced interfaces exist on device type
• YAML serialization for internal connections

Examples

PDU with circuits:

internal_connections:
  - from_interface: "Input"
    to_interfaces: ["Out 1", "Out 2", "Out 3", "Out 4"]
    connection_type: power-distribution
    circuit_name: "Bank A"
    breaker_amps: 20
  - from_interface: "Input"
    to_interfaces: ["Out 5", "Out 6", "Out 7", "Out 8"]
    connection_type: power-distribution
    circuit_name: "Bank B"
    breaker_amps: 20

Patch panel passthrough:

internal_connections:
  - from_interface: "Port 1 Front"
    to_interfaces: ["Port 1 Rear"]
    connection_type: passthrough
  - from_interface: "Port 2 Front"
    to_interfaces: ["Port 2 Rear"]
    connection_type: passthrough

Test Requirements

• InternalConnection schema validates correctly
• PDU device type with circuits serializes correctly
• Patch panel pass-through modeled correctly
• Invalid interface references are caught
• Internal connections used in path traversal

Related

• Parent Epic: feat: Connection Graph Model - Phase 1: Port-Based Architecture #362
• Enables: Power path visualization (feat: power port and outlet visualization #270)
• Enables: Patch panel pass-through (feat: patch panel pass-through visualization #269)