Feature: External event sources to trigger messages in active conversation

Problem

When Claude Code opens a PR, it has full implementation context — why decisions were made, what alternatives were considered, architectural reasoning. This makes it the best agent to address reviewer feedback (Copilot, human reviewers, other AI reviewers).

However, there's currently no way for an active Claude Code session to be notified when external events occur (e.g., a PR review is submitted). The user has to manually check and tell Claude to look at reviews.

Why existing solutions fall short

• claude-code-action (GitHub Action): Runs in a fresh context with no implementation history. It's a stranger reading a diff — fundamentally worse at addressing feedback than the session that wrote the code.
• Hooks: Only fire on internal lifecycle events (PreToolUse, PostToolUse, etc.) — no support for external triggers.
• MCP servers: Pull-only. Claude calls them; they can't push events into the conversation.
• Headless mode: Starts a new session, loses the conversational context.

Use case

1. Developer uses Claude Code to implement a feature and push a PR
2. Copilot / human / other AI submits a review
3. The same Claude Code session (with full context) gets notified and can address the feedback

Proposed direction

An event source / watcher system that can inject messages into the active conversation when external conditions change. Something like:

# Watch for new PR reviews
claude --watch "gh api repos/:owner/:repo/pulls/8/reviews" --on-change "New review submitted on PR #8"

Or as a hook event type:

{
  "event": "ExternalTrigger",
  "source": "github-pr-review",
  "command": "gh api repos/:owner/:repo/pulls/${PR_NUMBER}/reviews --jq 'length'",
  "poll_interval": "30s",
  "message": "New PR review received"
}

The primitives are all there — Claude Code is a running process that can spawn child processes, poll, or listen on sockets. The missing piece is a way to surface external events into the conversation loop.

Broader applicability

This isn't just about PR reviews. External event sources would enable:

• CI failure notifications while still in context
• Slack messages from teammates about the current work
• Deployment status updates
• Any webhook-driven workflow where context preservation matters