Feat/add mermaid chart rendering

[ARYPROGRAMMER]

Summary

Implements Mermaid chart rendering in Goose's chat UI as requested in issue #4222. This adds support for rendering interactive Mermaid diagrams (flowcharts, sequence diagrams, Gantt charts, etc.) directly inline in conversations, eliminating the need to copy-paste to external tools.

Type of Change

• Feature
• Bug fix
• Refactor / Code quality
• Performance improvement
• Documentation
• Tests
• Security fix
• Build / Release
• Other (specify below)

Testing

• Unit tests pass (cargo test -p goose-mcp test_render_mermaid)
• Code compiles without warnings (cargo build --package goose-mcp)
• Follows existing codebase patterns and conventions
• Debug HTML generation works for development verification
• MCP server integration tested

Related Issues

Relates to #4222
Discussion: #4222

Screenshots/Demos (for UX changes)

Before: Users had to copy-paste Mermaid code to external tools to visualize diagrams

After: Interactive Mermaid diagrams render directly inline in Goose's chat interface

Example diagram that will render:

graph TD;
    A-->B;
    A-->C;
    B-->D;
    C-->D;

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Changes

Core Implementation

• Added render_mermaid tool to AutoVisualiser MCP server with proper MCP-UI integration
• Created RenderMermaidParams struct for accepting Mermaid syntax as input
• Built mermaid_template.html with Mermaid.js integration and responsive styling
• Added mermaid.min.js (v10.9.0) to assets directory for client-side rendering

Documentation & Testing

• Updated AutoVisualiser MCP documentation to include Mermaid diagrams in the visualization types table
• Added test_render_mermaid unit test to verify tool functionality and MCP-UI resource generation
• Updated tool descriptions in the AutoVisualiser instructions

Technical Details

The implementation follows the existing AutoVisualiser pattern:

1. Accepts Mermaid syntax as string parameter via mermaid_code field
2. Replaces placeholders in HTML template with code and JS library
3. Returns base64-encoded HTML as MCP-UI resource for inline rendering
4. Generates debug HTML file to /tmp/mermaid.html for development inspection

Files Changed

• crates/goose-mcp/src/autovisualiser/mod.rs - Added tool implementation and tests
• crates/goose-mcp/src/autovisualiser/templates/mermaid_template.html - New HTML template
• crates/goose-mcp/src/autovisualiser/templates/assets/mermaid.min.js - Mermaid.js library
• documentation/docs/mcp/autovisualiser-mcp.md - Updated documentation

Email: [email protected]

[blackgirlbytes]

Hi @DOsinga , @alexhancock , @aharvard

This PR intends to add mermaid chart rendering via Autviz and MCP UI to goose. Flagging you all to review.

Thank you!

[ARYPROGRAMMER]

reminder to review, 1 test is failing as the github repo creds for api keys are not set. rest LGTM to me in recheck

[ARYPROGRAMMER]

can this be completed today? @maintainers

[taniandjerry]

Hi @ARYPROGRAMMER ! Thank you for waiting, the dev team will get to this as soon as they can!

[alexhancock]

LGTM if it also does to @michaelneale

[alexhancock]

Test failures in https://github.com/block/goose/actions/runs/18807497526/job/53674602193?pr=5377 are likely unrelated

[michaelneale]

nice I like @ARYPROGRAMMER !

@alexhancock I just realised those failures are probably as forks don't have access to those secrets... need to think what systemic solution is for that (I think for forks we can skip that part of the job, keep it for branches)

[blackgirlbytes]

i'm merging!

[alexhancock]

Nice! Thanks for this one, will be fun to use