[FEATURE] Feature Request: Allow custom content injection into the TUI bottom status bar

Summary

Claude Code's TUI displays a dynamic status bar at the bottom right of the interface, showing runtime information like token usage, model name, and tool call status. We'd like the ability to inject custom content into this area (or a dedicated region near it).

Motivation

When running multiple Claude Code instances simultaneously — each working in a different directory or on a different project — it becomes easy to lose track of which session belongs to which context. This confusion increases with the number of concurrent sessions.

Our current workaround is to use a shell wrapper that overrides the claude command and prints the working directory and git branch via PS1/RPROMPT before the session starts:

function claude() {
  local branch=$(git branch --show-current 2>/dev/null)
  print -P "%F{cyan}[Claude Code]%f Working dir: %F{yellow}$(pwd)%f  %F{green}($branch)%f"
  command claude "$@"
}

This only works at startup and disappears once the TUI takes over. There is no way to keep this information persistently visible inside the Claude Code UI itself.

We believe this is a common pain point for power users managing multiple concurrent Claude Code sessions, and an official injection mechanism for the status bar would be a clean, first-class solution.

Proposed API

A lightweight extension point, for example via ~/.claude/settings.json:

{
  "statusBar": {
    "right": "$(pwd) | $(git branch --show-current)"
  }
}

Or via a hook that can emit structured output consumed by the TUI renderer:

{
  "hooks": {
    "StatusBar": [
      {
        "type": "command",
        "command": "echo \"{\\\"text\\\": \\\"$(pwd)\\\"}\""
      }
    ]
  }
}

Expected Behavior

• Custom content is evaluated at session start (and optionally refreshed periodically)
• Displayed in the bottom bar without interfering with Claude's normal operation
• Supports basic shell command interpolation

Use Cases

• Always-visible working directory and git branch
• Project name / environment indicator
• Custom session labels when running multiple Claude Code instances