docs: Add opencode-canvas plugin to ecosystem

[harshav167]

Summary

Adds opencode-canvas to the ecosystem page.

opencode-canvas is a plugin that gives OpenCode its own display. Instead of text-only responses, the AI can spawn interactive terminal interfaces in tmux split panes.

Features

• Calendar views - Visual date pickers, event displays, and meeting time selection
• Document editors - Rich markdown rendering with text selection support
• Flight booking - Interactive flight search with seat map selection
• IPC communication - Real-time bidirectional updates between OpenCode and canvases

Tools Provided

Tool	Description
canvas_spawn	Create a new canvas (calendar, document, or flight) in a tmux split
canvas_update	Update canvas state via IPC
canvas_selection	Get current selection from canvas (dates, text, seats)
canvas_close	Close a canvas session

Installation

npm install @mailshieldai/opencode-canvas

Add to opencode.jsonc:

{
  "plugin": ["@mailshieldai/opencode-canvas"],
  "permission": {
    "canvas_*": "allow"
  }
}

Requirements

• Bun - JavaScript runtime
• tmux - Canvases spawn in split panes
• OpenCode - AI coding assistant

Based on claude-canvas by David Siegel, adapted for OpenCode.

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