D-21: AgentSessionFeature — Presentation enum + ifCaseLet scope

[kirich1409]

Description

Refactor AgentSessionFeature.State to hold an immutable Presentation enum wrapping either TerminalFeature.State or AgentChatFeature.State. Switch reducer composition from Scope to ifCaseLet accordingly.

Spec: Epic #250 §5 (session surface model — Presentation enum).

Scope

File

MacApp/Packages/AgentOrchestrator/Sources/AgentOrchestrator/AgentSessionFeature.swift

Before / after

Before:
```swift
public struct State {
public var session: AgentSession
public var terminal: TerminalFeature.State
public var kind: SessionKind
...
}
```

After:
```swift
public struct State {
public var session: AgentSession // contains immutable surface
public var presentation: Presentation
public var kind: SessionKind
...

public enum Presentation: Equatable {
    case terminal(TerminalFeature.State)
    case dialogue(AgentChatFeature.State)
}

}

public enum Action {
case startAgent(workingDirectory: URL)
case stopAgent
case restartAgent
case terminal(TerminalFeature.Action)
case dialogue(AgentChatFeature.Action)
case _claudeDetected(ClaudeInstallation, shellPATH: String?)
case _agentStarted
case _agentStopped(exitCode: Int32)
}

public var body: some ReducerOf {
Reduce { state, action in /* lifecycle */ }
.ifCaseLet(.presentation.terminal, action: .terminal) {
TerminalFeature()
}
.ifCaseLet(.presentation.dialogue, action: .dialogue) {
AgentChatFeature()
}
}
```

Initialization

• .agentTerminal(.claudeCode) — initial Presentation.terminal(.init()).
• .agentDialogue(.claudeCode) — initial Presentation.dialogue(.init(sessionID:, agentKind:)).
• Initialization happens at AgentOrchestratorFeature when creating a new session (surface chosen by caller).

Lifecycle routing

startAgent action builds the correct command via ClaudeCommandBuilder (D-20), starts the underlying TerminalSession via the appropriate sub-feature:

• Terminal surface: delegates to TerminalFeature start action.
• Dialogue surface: creates ClaudeCodeJSONLSession (D-9), dispatches .dialogue(._startSession(...)).

Acceptance Criteria

• AgentSessionFeature.State refactored with presentation enum.
• Reducer composes via ifCaseLet for both presentations.
• Terminal regression: existing terminal sessions still work (unit tests pass).
• Dialogue session can be created with correct initial Presentation and lifecycle hooks into underlying Dialogue session.
• TestStore coverage for transitions: start → running → exit for both surfaces.
• Swift 6 strict concurrency clean.

Relationships

• Parent issue: EPIC: Dialogue — structured chat UI for agent sessions #250
• Blocked by: #D-10, #D-20, D-6: SharedModels — introduce SessionSurface enum #256 (SessionSurface)
• Blocks: #D-22, #D-23