SOLID Principles

Every module in AgentsBoard enforces SOLID principles. Here's how each principle is applied.

Single Responsibility (SRP)

Each class has one reason to change:

Class	Responsibility
PTYProcess	Fork and manage a single PTY
VTParser	Parse VT100 escape sequences
CostEngine	Aggregate cost data
FleetManager	Track active sessions
RecordingEngine	Write Asciicast v2 files

Open/Closed (OCP)

New functionality is added through extension, not modification:

// New agent providers are added by conforming to protocols
// No existing code needs to change
public protocol AgentDetectable {
    func detect(command: String, initialOutput: String) -> AgentInfo?
}

// Register at runtime
registry.register(myNewDetector)

OCP in practice:

• ProviderRegistry — register new agent detectors without modifying existing code
• CommandRegistry — add commands via CommandProviding protocol
• MCPServer — register new tools at runtime
• ThemeEngine — add themes without touching existing ones

Liskov Substitution (LSP)

All protocol implementations are fully substitutable:

// Any FleetManaging implementation works here
func showStats(fleet: any FleetManaging) {
    let stats = fleet.stats
    print("Active: \(stats.activeSessions)")
}

Interface Segregation (ISP)

Agent capabilities are split into 4 narrow protocols instead of one large one:

public protocol AgentDetectable { ... }      // Detection
public protocol AgentStateObservable { ... } // State tracking
public protocol AgentCostReportable { ... }  // Cost reporting
public protocol AgentControllable { ... }    // Control actions

A simple agent might only implement AgentDetectable, while a full-featured one implements all four.

Dependency Inversion (DIP)

High-level modules depend on abstractions, not concretions:

// Core defines the protocol
public protocol PersistenceProviding {
    func save<T: Codable & Identifiable>(_ record: T, in table: String) throws
    func fetch<T: Codable & Identifiable>(from table: String, id: String) throws -> T?
    // ...
}

// Implementation uses GRDB (but Core doesn't know about GRDB)
final class DatabaseManager: PersistenceProviding { ... }

// CompositionRoot wires them together
let persistence: any PersistenceProviding = DatabaseManager()

DIP wrappers:

• PersistenceProviding wraps GRDB/SQLite
• YAMLParsing wraps Yams
• TerminalSessionManaging wraps SwiftTerm + PTY
• ThemeProviding wraps the theme engine