[FEATURE] Config option to default /resume session picker to "all projects" view

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

The /resume session picker defaults to showing sessions from the current directory only. Toggling to \"all projects\" requires pressing Ctrl+A in the picker UI — but this conflicts with common terminal multiplexer prefix keys. For example, many tmux users set prefix C-a, which means tmux intercepts the keystroke before it ever reaches Claude Code, making the \"all projects\" toggle completely inaccessible without workarounds.

There is currently no configuration option to change the default scope of the picker.

Proposed Solution

Add a settings.json option to default the session picker to \"all projects\" mode:

{
  "resumeDefaultScope": "all"
}

Accepted values:

• "current" — current directory only (existing default behavior)
• "all" — all projects across the machine

This would allow users who work across multiple projects — or who cannot use Ctrl+A due to terminal conflicts — to access all their sessions without workarounds.

Alternative Solutions

• Change the tmux prefix key (disruptive to existing muscle memory)
• Run claude outside of tmux (inconvenient)
• Make the toggle keybinding configurable (also acceptable, but a config default is simpler)

Priority

Medium — quality of life for multi-project workflows and tmux users

Feature Category

CLI / session management

Related Issues

• #23146 — similar keyboard conflict on Windows where Ctrl+V (used in the picker) conflicts with the system paste shortcut
• #34985 — VSCode-specific version of this request (all-projects picker toggle for IDE extension)

Additional Context

Affects any user whose terminal environment intercepts Ctrl+A before it reaches Claude Code — this includes tmux (set -g prefix C-a is a very common configuration), GNU Screen (also uses Ctrl+A by default), and potentially other multiplexers.