OpenCode 2 ships three breaking changes, one silently kills v1 plugins

A hands-on upgrade to OpenCode 2.0.28 found three breaking changes: v1 plugins fail to load with only a WARN log, tui.json migrates to cli.json only on first TUI start, and the server API moves to @opencode/client. The upgrade took over 8 minutes and left v1 installed alongside v2 on a custom prefix.

• v1 plugins fail with a WARN while the server keeps running
• tui.json becomes cli.json only when a TTY starts
• bash and edit become shell and edit, MCP moves under mcp.servers
• With a custom prefix v1 and v2 coexist, PATH decides which runs