research(tools): Claude Code Monitor tool — stream background process events into agent context

[bug-ops]

Description

Claude Code v2.1.100+ added a Monitor tool that allows the agent to subscribe to streaming stdout events from background processes and receive notifications as events arrive. This enables the agent to watch long-running scripts without polling.

Pattern

The Monitor tool works in conjunction with background script execution:

1. Start a background process (e.g., a test runner, build, or server)
2. Call Monitor with the process reference to receive a stream of stdout lines as tool events
3. Agent reacts to events (e.g., test failure, build complete) without sleeping or polling

Relevance to Zeph

Zeph's zeph-tools provides ShellExecutor which currently blocks until completion. Adding a Monitor-style streaming mode would enable:

• Long-running tool outputs streamed into context as they arrive
• TUI status updates from background builds / test runs
• Hook-based reactions to specific stdout patterns (e.g., fire a PostToolUse hook when output contains "error")

Implementation Sketch

Add ShellExecutorMode::Streaming variant to ToolExecutor:

• Spawn process, return AsyncStream<ToolEvent>
• Each stdout line = one ToolEvent::Partial
• On process exit: ToolEvent::Complete with exit code

Expose in TUI as a spinner with live output tail.

Source

• Claude Code CHANGELOG v2.1.100: Monitor tool for streaming background script events
• https://code.claude.com/docs/en/changelog