cli: no way to refresh environment variables without restarting

Summary

After modifying system/user environment variables (e.g., adding a new directory to PATH), OpenCode does not detect the changes until a full restart. There is no built-in way to refresh environment variables within a running session.

Environment

• opencode version: 2.0.3
• OS: Windows_NT 10.0.26200 (win32 x64)
• Shell: Git Bash (MINGW64)

Reproduction

1. Install a CLI tool to a new directory (e.g., D:\Tools\gh\bin\)
2. Add the directory to the user PATH via system settings
3. In an active OpenCode session, try to use the tool: gh --version
4. Command not found — the new PATH is not reflected

Expected Behavior

OpenCode should either:

• Re-read environment variables on demand (e.g., a refresh-env command or API)
• Or detect PATH changes and update the shell environment automatically

Actual Behavior

The only workaround is to fully restart OpenCode. All running sessions, context, and state are lost.

Additional Context

This affects any workflow where tools are installed or environment variables are modified mid-session. Common scenarios:

• Installing new CLI tools (gh, docker, etc.) via package managers
• Modifying proxy settings (HTTP_PROXY, NO_PROXY)
• Switching Node.js versions via nvm
• Updating API keys or tokens stored in env vars