Add timeout and fix resource leaks in Git client

Sources/SwiftCommitGen/Core/CommitGenError.swift

@@ -4,6 +4,7 @@ import Foundation
 enum CommitGenError: Error {
   case gitRepositoryUnavailable
   case gitCommandFailed(message: String)
+  case gitCommandTimedOut(command: String, timeout: TimeInterval)
   case cleanWorkingTree
   case modelUnavailable(reason: String)
   case modelTimedOut(timeout: TimeInterval)
@@ -18,6 +19,8 @@ extension CommitGenError: LocalizedError {
       "Failed to locate a Git repository in the current directory hierarchy."
     case .gitCommandFailed(let message):
       message.isEmpty ? "Git command failed for an unknown reason." : message
+    case .gitCommandTimedOut(let command, let timeout):
+      "Git command '\(command)' did not complete within \(formatSeconds(timeout))."
     case .cleanWorkingTree:
       "No pending changes detected; nothing to summarize."
     case .modelUnavailable(let reason):

Sources/SwiftCommitGen/Core/GitClient.swift

@@ -254,7 +254,10 @@ struct SystemGitClient: GitClient {
     return result
   }
 
-  private func runGit(_ arguments: [String]) throws -> String {
+  /// Default timeout for git operations in seconds.
+  private static let gitCommandTimeout: TimeInterval = 60
+
+  private func runGit(_ arguments: [String], timeout: TimeInterval = gitCommandTimeout) throws -> String {
     let process = Process()
     process.executableURL = URL(fileURLWithPath: "/usr/bin/env")
     process.arguments = ["git"] + arguments
@@ -268,30 +271,63 @@ struct SystemGitClient: GitClient {
     environment["LC_ALL"] = "C"
     process.environment = environment
 
+    // Ensure file handles are always closed to prevent descriptor leaks
+    defer {
+      try? stdoutPipe.fileHandleForReading.close()
+      try? stderrPipe.fileHandleForReading.close()
+    }
+
     do {
       try process.run()
     } catch {
       throw CommitGenError.gitCommandFailed(message: error.localizedDescription)
     }
 
-    // IMPORTANT: Read from pipes BEFORE waiting for exit to avoid deadlock.
-    // If the output exceeds the pipe buffer (~64KB), the process will block
-    // waiting to write more data, causing a deadlock if we wait for exit first.
-    let stdoutData = stdoutPipe.fileHandleForReading.readDataToEndOfFile()
-    let stderrData = stderrPipe.fileHandleForReading.readDataToEndOfFile()
+    // Read from pipes with timeout using DispatchGroup.
+    // IMPORTANT: Read BEFORE waiting for exit to avoid deadlock when output
+    // exceeds the pipe buffer (~64KB).
+    let readGroup = DispatchGroup()
+    let stdoutBox = DataBox()
+    let stderrBox = DataBox()
+
+    readGroup.enter()
+    DispatchQueue.global(qos: .userInitiated).async {
+      stdoutBox.value = stdoutPipe.fileHandleForReading.readDataToEndOfFile()
+      readGroup.leave()
+    }
+
+    readGroup.enter()
+    DispatchQueue.global(qos: .userInitiated).async {
+      stderrBox.value = stderrPipe.fileHandleForReading.readDataToEndOfFile()
+      readGroup.leave()
+    }
+
+    let waitResult = readGroup.wait(timeout: .now() + timeout)
+
+    if waitResult == .timedOut {
+      process.terminate()
+      let command = arguments.first ?? "unknown"
+      throw CommitGenError.gitCommandTimedOut(command: command, timeout: timeout)
+    }
 
     process.waitUntilExit()
 
     guard process.terminationStatus == 0 else {
-      let stderr = String(data: stderrData, encoding: .utf8) ?? ""
+      let stderr = String(data: stderrBox.value ?? Data(), encoding: .utf8) ?? ""
       let message = stderr.trimmingCharacters(in: .whitespacesAndNewlines)
       throw CommitGenError.gitCommandFailed(message: message)
     }
 
-    return String(data: stdoutData, encoding: .utf8) ?? ""
+    return String(data: stdoutBox.value ?? Data(), encoding: .utf8) ?? ""
   }
 }
 
+/// Thread-safe container for passing data across dispatch queues.
+/// Allows concurrent read/write without Swift concurrency warnings.
+private final class DataBox: @unchecked Sendable {
+  var value: Data?
+}
+
 struct GitStatusParser {
   static func parse(_ raw: String) -> GitStatus {
     var staged: [GitFileChange] = []

Tests/SwiftCommitGenTests/BatchCombinationPromptBuilderTests.swift

@@ -93,7 +93,7 @@ struct BatchCombinationPromptBuilderTests {
     #expect(package.diagnostics.estimatedLineCount >= 14)
 
     let instructions = String(describing: package.systemPrompt)
-    #expect(instructions.contains("You are an AI assistant"))
+    #expect(instructions.contains("Combine these partial commit drafts"))
     #expect(instructions.contains("Style: use the body for a few short sentences"))
   }