Add AI commit and PR generation with pluggable providers

Muxy/Models/VCSTabState.swift

@@ -92,6 +92,7 @@ final class VCSTabState {
     var isCommitting = false
     var isPushing = false
     var isPulling = false
+    var isGeneratingCommitMessage = false
     var isSwitchingBranch = false
     var isLoadingBranches = false
     var statusMessage: String?
@@ -182,6 +183,7 @@ final class VCSTabState {
     @ObservationIgnored private var commitLogTask: Task<Void, Never>?
     @ObservationIgnored private var prListTask: Task<Void, Never>?
     @ObservationIgnored private var prAutoSyncTask: Task<Void, Never>?
+    @ObservationIgnored private var aiGenerationTask: Task<Void, Never>?
     @ObservationIgnored private var watcher: FileSystemWatcher?
     @ObservationIgnored nonisolated(unsafe) private var remoteChangeObserver: NSObjectProtocol?
     @ObservationIgnored private var isRefreshing = false
@@ -659,6 +661,42 @@ final class VCSTabState {
         }
     }
 
+    func generateCommitMessageWithAI() {
+        guard hasAnyChanges else {
+            showStatus("No changes to summarize.", isError: true)
+            return
+        }
+        if isGeneratingCommitMessage { return }
+        isGeneratingCommitMessage = true
+        let path = projectPath
+        let branch = branchName
+        aiGenerationTask?.cancel()
+        aiGenerationTask = Task { [weak self] in
+            do {
+                let message = try await AIAssistantService.generateCommitMessage(
+                    repoPath: path,
+                    branch: branch
+                )
+                guard let self, !Task.isCancelled else { return }
+                commitMessage = message
+            } catch is CancellationError {
+                return
+            } catch {
+                guard let self, !Task.isCancelled else { return }
+                showStatus(errorText(error), isError: true)
+            }
+            guard let self else { return }
+            isGeneratingCommitMessage = false
+            aiGenerationTask = nil
+        }
+    }
+
+    func cancelCommitMessageGeneration() {
+        aiGenerationTask?.cancel()
+        aiGenerationTask = nil
+        isGeneratingCommitMessage = false
+    }
+
     func push() {
         isPushing = true
         Task { [weak self] in

Muxy/Services/AIAssistant/AIAssistantPrompts.swift

@@ -0,0 +1,65 @@
+import Foundation
+
+enum AIAssistantTask {
+    case commitMessage
+    case pullRequest
+}
+
+enum AIAssistantPrompts {
+    static let defaultCommitUserPrompt = """
+    Write a concise, conventional git commit message for the staged changes below.
+    - Subject line in imperative mood, max 72 characters.
+    - Optional body, wrapped at 72 characters, explaining the why.
+    - Do not include code fences, quotes, or any extra commentary.
+    """
+
+    static let defaultPullRequestUserPrompt = """
+    Write a pull request title and short description for the diff below.
+    - Title: short, imperative, max 70 characters.
+    - Description: 1-3 short bullet points or sentences focused on the why.
+    - Do not include code fences or extra commentary.
+    """
+
+    static func systemPrompt(for task: AIAssistantTask) -> String {
+        switch task {
+        case .commitMessage:
+            """
+            You are an assistant that generates git commit messages.
+            Output ONLY the commit message in plain text. No code fences, no preamble, no JSON.
+            Subject line first, then a blank line, then optional body. No trailing notes.
+            """
+        case .pullRequest:
+            """
+            You are an assistant that generates pull request metadata.
+            Output ONLY a single JSON object with exactly two string keys: "title" and "body".
+            No code fences, no preamble, no trailing text. Example:
+            {"title": "Fix crash on launch", "body": "Avoid blocking DNS by removing hostName lookup."}
+            """
+        }
+    }
+
+    static func composedPrompt(
+        for task: AIAssistantTask,
+        userPrompt: String,
+        diff: String,
+        branch: String?,
+        baseBranch: String?
+    ) -> String {
+        let trimmedUser = userPrompt.trimmingCharacters(in: .whitespacesAndNewlines)
+        var sections: [String] = [systemPrompt(for: task), trimmedUser]
+
+        var contextLines: [String] = []
+        if let branch, !branch.isEmpty {
+            contextLines.append("Current branch: \(branch)")
+        }
+        if let baseBranch, !baseBranch.isEmpty {
+            contextLines.append("Base branch: \(baseBranch)")
+        }
+        if !contextLines.isEmpty {
+            sections.append(contextLines.joined(separator: "\n"))
+        }
+
+        sections.append("Diff:\n\(diff)")
+        return sections.joined(separator: "\n\n")
+    }
+}

Muxy/Services/AIAssistant/AIAssistantProvider.swift

@@ -0,0 +1,54 @@
+import Foundation
+
+enum AIAssistantProvider: String, CaseIterable, Identifiable, Codable {
+    case claude
+    case codex
+    case opencode
+    case custom
+
+    var id: String { rawValue }
+
+    var displayName: String {
+        switch self {
+        case .claude: "Claude Code"
+        case .codex: "Codex"
+        case .opencode: "OpenCode"
+        case .custom: "Custom Command"
+        }
+    }
+
+    var defaultExecutable: String {
+        switch self {
+        case .claude: "claude"
+        case .codex: "codex"
+        case .opencode: "opencode"
+        case .custom: ""
+        }
+    }
+
+    func builtInArguments(model: String?) -> [String] {
+        switch self {
+        case .claude:
+            var args = ["-p", "--output-format", "text"]
+            if let model, !model.isEmpty {
+                args.append(contentsOf: ["--model", model])
+            }
+            return args
+        case .codex:
+            var args = ["exec", "--skip-git-repo-check"]
+            if let model, !model.isEmpty {
+                args.append(contentsOf: ["--model", model])
+            }
+            args.append("-")
+            return args
+        case .opencode:
+            var args = ["run"]
+            if let model, !model.isEmpty {
+                args.append(contentsOf: ["--model", model])
+            }
+            return args
+        case .custom:
+            return []
+        }
+    }
+}