Mailshieldai Opencode Canvas Document

Document Canvas

Display markdown documents with optional text selection and diff highlighting.

Example Prompts

Try asking Claude:

• "Draft an email to the marketing team about the Q1 product launch"
• "Help me edit this blog post - show it so I can highlight the parts to revise"
• "Write a project proposal and let me review it"
• "Show me the README so I can select sections to update"
• "Compose a response to this customer complaint"

Scenarios

display (default)

Read-only document view with markdown rendering. User can scroll but cannot select text.

canvas_spawn({
  kind: "document",
  scenario: "display",
  config: JSON.stringify({
    content: "# Hello World\n\nThis is **markdown** content.",
    title: "My Document"
  })
})

edit

Interactive document view with text selection. User can click and drag to select text, which is sent via IPC in real-time.

• Renders markdown with syntax highlighting (headers, bold, italic, code, links, lists, blockquotes)
• Diff highlighting: green background for additions, red for deletions
• Click and drag to select text
• Selection automatically sent via IPC

canvas_spawn({
  kind: "document",
  scenario: "edit",
  config: JSON.stringify({
    content: "# My Blog Post\n\nThis is the **introduction** to my post.\n\n## Section One\n\n- Point one\n- Point two",
    title: "Blog Post Draft",
    diffs: [
      {startOffset: 50, endOffset: 62, type: "add"}
    ]
  })
})

email-preview

Specialized view for email content display.

canvas_spawn({
  kind: "document",
  scenario: "email-preview",
  config: JSON.stringify({
    content: "Dear Team,\n\nPlease review the attached document.\n\nBest regards,\nAlice",
    title: "RE: Project Update"
  })
})

Configuration

interface DocumentConfig {
  content: string;        // Markdown content
  title?: string;         // Document title (shown in header)
  diffs?: DocumentDiff[]; // Optional diff markers for highlighting
  readOnly?: boolean;     // Disable selection (default: false for edit)
}

interface DocumentDiff {
  startOffset: number;    // Character offset in content
  endOffset: number;
  type: "add" | "delete";
}

Markdown Rendering

Supported markdown features:

• Headers (# H1, ## H2, etc.)
• Bold (**text**)
• Italic (*text*)
• Code (`inline` and fenced blocks)
• Links ([text](url))
• Lists (- or * bullets)
• Blockquotes (>)

Selection Result

interface DocumentSelection {
  selectedText: string;   // The selected text
  startOffset: number;    // Start character offset
  endOffset: number;      // End character offset
  startLine: number;      // Line number (1-based)
  endLine: number;
  startColumn: number;    // Column in start line
  endColumn: number;
}

Controls

• Mouse click and drag: Select text (edit scenario)
• Up/Down or scroll: Navigate document
• q or Esc: Close/cancel

API Usage

// Display read-only document
canvas_spawn({
  kind: "document",
  scenario: "display",
  config: JSON.stringify({
    content: "# My Document\n\nContent here.",
    title: "View Mode",
  })
});

// Interactive editing with selection
canvas_spawn({
  kind: "document",
  scenario: "edit",
  config: JSON.stringify({
    content: "# My Document\n\nSelect some **text** here.",
    title: "Edit Mode",
    diffs: [{ startOffset: 20, endOffset: 30, type: "add" }],
  })
});

// Get current selection from a running canvas
canvas_selection({ id: "document-1234567890-abc123" });
// Returns: { success: true, selection: { selectedText: "text", startOffset: 30, endOffset: 34 } }

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