Runner log viewer — view and export runner logs from GUI and CLI

[nicktallen]

Problem

When a runner misbehaves or a workflow fails on a self-hosted runner, users need to inspect runner logs to diagnose the issue. Currently there's no built-in way to view, search, or export runner process logs from the app. Users must find and manually inspect log files on disk.

Proposed Solution

Add log viewing capabilities to both GUI and CLI:

CLI:

mac-runner logs my-runner          # tail recent logs
mac-runner logs my-runner --follow # stream logs in real-time
mac-runner logs my-runner --lines 100  # last N lines

GUI:

• "View Logs" option in runner context menu / detail view
• Scrollable log viewer with search/filter
• Copy-to-clipboard and export options

Acceptance Criteria

• CLI logs subcommand with tail, follow, and line-count options
• GUI log viewer accessible per-runner
• Search/filter within logs
• Log rotation to prevent unbounded disk usage
• Works for all isolation modes

[nicktallen]

Triage note — Runner logs already exist on disk at:

~/.mac-runner/runners/{uuid}/runner.log

Each runner routes stdout/stderr to its log file. The infrastructure is there — this issue is specifically about building an in-app viewer (and possibly a mac-runner logs <name> CLI subcommand).

For the GUI, a LogViewerView could tail the file using a DispatchSource.makeFileSystemObjectSource for real-time updates. For CLI, a simple tail -f wrapper would work.