Feature Request: Include sse_port in SessionStart hook input

Summary

The SessionStart hook currently does not include the CLAUDE_CODE_SSE_PORT in its JSON input. This makes it impossible to reliably register sessions with external integrations at session start.

Problem

At SessionStart, the CLAUDE_CODE_SSE_PORT environment variable may contain a stale value inherited from the parent shell (e.g., from a previous Claude Code session in another terminal). The fresh SSE port is only reliably available after Claude Code starts, but before hooks can access it.

Current SessionStart input:

{
  "session_id": "abc123-...",
  "cwd": "/path/to/project"
}

Desired SessionStart input:

{
  "session_id": "abc123-...",
  "cwd": "/path/to/project",
  "sse_port": "54321"
}

Use Case

I'm building Colin Whisper, a voice-first terminal automation overlay that integrates with Claude Code. The overlay maintains a SessionStore that maps SSE ports to terminals for:

• Real-time session tracking across multiple terminals
• Per-terminal task visualization
• Timer management
• Voice routing to specific Claude Code sessions

Currently, session registration only happens on UserPromptSubmit (first prompt) because that's when CLAUDE_CODE_SSE_PORT becomes reliable. This means:

1. User launches claude in a terminal
2. Gap: Session exists but overlay doesn't know about it
3. User sends first prompt → session finally registers

Including sse_port in SessionStart would allow immediate registration.

Proposed Solution

Include the SSE port in the SessionStart hook's JSON input, similar to how session_id is already included. This would be the freshly-assigned port for the current Claude Code instance, not the inherited environment variable.

Workaround Attempted

I tried reading CLAUDE_CODE_SSE_PORT from the environment in SessionStart hook, but it contains the stale port from a previous session (inherited from parent shell), not the current session's port.

Environment

• Claude Code version: latest
• OS: macOS
• Shell: zsh/bash