sanieldoe/companions/canvas-builder

Reading the Current Canvas

The canvas is a file in the vault. Before updating, always read it first:

• Path: projects/<current-project-slug>/canvas.json
• Use the read tool to load it, then emit the full updated canvas with your changes merged in.
• If the file doesn't exist yet, start fresh.

Critical Rules

• Output <canvas> as a raw tag — never inside backticks or code fences.
• Put <canvas> at the END of your response, after all conversational text.
• Always include ALL existing blocks — the full canvas replaces the previous one. Never drop blocks the user hasn't removed.
• IDs are short and stable: b1, b2, b3 for blocks; t1, t2 for task items.

When to Emit a Canvas

• User asks to add something to their canvas or Shapeshifter tab.
• You produce a plan, outline, checklist, or structured artifact worth persisting.
• A key decision, reference, or resource should stay permanently visible.
• The project's scope or status changes meaningfully.

Output Format

<canvas> { "blocks": [ { "id": "b1", "type": "markdown", "content": "# Title\n\nOne-line description." }, { "id": "b2", "type": "tasks", "title": "Next steps", "items": [ { "id": "t1", "text": "Do the thing", "done": false } ]}, { "id": "b3", "type": "note", "title": "Key insight", "content": "Main idea.", "color": "amber" } ] } </canvas>

Block Types

This is a fixed block system — 10 types total. You cannot render arbitrary UI; compose these blocks to represent any content.

input block note: Omit content when creating — the app fills it in as the user types. Schema: { "id": "b1", "type": "input", "title": "Optional label" }

html block note: Write complete, self-contained HTML — all CSS in <style> tags, all JS in <script> tags, no external CDN links. Omit height to let the app measure automatically. Use for charts, tables, custom layouts, or anything the other block types can't express.

Example — Talk Prep Canvas

Your conversational reply goes here, then immediately after:

<canvas> { "blocks": [ { "id": "b1", "type": "markdown", "content": "# Friend Zone Talk\n\nOne point: Real friendship requires risk.\n\nKey phrase: You can't stay safe and stay close at the same time." }, { "id": "b2", "type": "tasks", "title": "Prep checklist", "items": [ { "id": "t1", "text": "Write the ME opening story", "done": false }, { "id": "t2", "text": "Find the WE illustration", "done": false }, { "id": "t3", "text": "Memorise the key phrase", "done": false } ]}, { "id": "b3", "type": "note", "title": "Opening tension", "content": "Everyone wants deep friendship. Almost nobody risks the vulnerability it requires.", "color": "blue" } ] } </canvas>

Composition Note

This is a fixed block system with 10 types. Agents cannot render arbitrary UI — only compose these blocks. Any content that doesn't fit a block type should be expressed as markdown.