Default agent-shell-start wrapper and Emacs-native bootstrapping

[robjgray]

Description

This provides a 'batteries included' wrapper for starting agent-shell and an Emacs-native bootstrap option. Users can still point it at a fully custom starter if they want.

Main changes

• Adds meta-agent-shell-setup as an Emacs-native alternative to the current setup script
• Adds a package-owned default wrapper around agent-shell-start
• Preserves the startup behavior meta-agent-shell expects for:
  • buffer naming
  • project-root vs current-directory startup
  • the internal 'use-current-dir path used for programmatic named-agent starts
• Adds package-owned customization points for session policy / provider mode mapping
  • Codex defaults rely on a pre-release agent-shell variable. Latest version 0.46.1 specified for now.
• Updates README docs for setup and customization
• Adds focused test coverage for these changes

Additional changes

• Updated meta-agent-shell-test-ask-session
• Made the following tests more durable in sandboxed environments:
  • meta-agent-shell-test-view-session
  • meta-agent-shell-test-close-session
  • meta-agent-shell-test-full-workflow

Maintainer notes

• The default wrapper is based on the maintainer’s starter which was referenced in code. @ElleNajt if I missed some necessary details or style preferences, I'm happy to make changes. Users who prefer their own starter can still do something like:

(setq meta-agent-shell-start-function
      #'my/agent-shell-anthropic-start-claude-code)

• I considered taking additional steps to make this more agent-agnostic, but figured it would be better as its own effort.

Type of Changes

• Bug fix
• New feature
• Documentation update
• Code refactoring

Related Issues

Fixes #1

Testing

• Unit tests added/updated
• Manual testing performed

Ran:

emacs -Q -batch -L . -l ert -l meta-agent-shell-test.el -f ert-run-tests-batch-and-exit