Create diagrams with Mermaid

Create a diagram from the most recent interaction context using Mermaid. Generate a PNG image with a transparent background and output it as a markdown image so it renders inline.

How to create a diagram

1. Extract or derive diagrammable data from the current context.
2. If the Emacs foreground color and background mode are not already known from a previous diagram in this session, query them:

   emacsclient --eval '(face-foreground (quote default))'
   emacsclient --eval '(frame-parameter nil (quote background-mode))'
   

   The first returns a hex color like "#eeffff". The second returns dark or light. Reuse both for all subsequent diagrams.
3. Write a Mermaid file to a temporary file.
4. Write a JSON config file that overrides theme variables with the queried foreground color. Set "theme" to "dark" or "default" based on the background mode.
5. Run mmdc with -t dark if background mode is dark, or -t default if light.
6. Output the result as a markdown image on its own line:

   ![description](/tmp/agent-diagram-XXXX.png)
   

# Use -t dark for dark, -t default for light
PUPPETEER_EXECUTABLE_PATH=/opt/homebrew/bin/chromium mmdc \
  -i /tmp/agent-diagram-XXXX.mmd \
  -o /tmp/agent-diagram-XXXX.png \
  -t dark -b transparent --scale 2 \
  --configFile /tmp/agent-diagram-XXXX-config.json

Mermaid config template

Write this JSON config file to apply the Emacs foreground color. Replace #eeffff with the queried color. Set "theme" to "dark" or "default" based on the Emacs background mode.

{
  "theme": "dark",
  "themeVariables": {
    "primaryTextColor": "#eeffff",
    "secondaryTextColor": "#eeffff",
    "tertiaryTextColor": "#eeffff",
    "primaryBorderColor": "#eeffff",
    "lineColor": "#eeffff",
    "textColor": "#eeffff",
    "actorTextColor": "#eeffff",
    "actorBorder": "#eeffff",
    "signalColor": "#eeffff",
    "signalTextColor": "#eeffff",
    "labelTextColor": "#eeffff",
    "loopTextColor": "#eeffff",
    "noteTextColor": "#eeffff",
    "noteBorderColor": "#eeffff",
    "sectionTextColor": "#eeffff",
    "titleColor": "#eeffff"
  }
}

Mermaid diagram template

sequenceDiagram
    participant a as Alice
    participant b as Bob
    a->>b: Hello
    b-->>a: Hi back

Rules

• Query the Emacs foreground color once per session and reuse it for all subsequent diagrams. Only query again if the color is not already known.
• Query the Emacs background mode once per session via (frame-parameter nil 'background-mode). Use -t dark for dark or -t default for light. Always use -b transparent --scale 2.
• Always use PUPPETEER_EXECUTABLE_PATH=/opt/homebrew/bin/chromium when invoking mmdc.
• Always write a JSON config file with themeVariables set to the queried foreground color and pass it via --configFile.
• Always use a timestamp in the filename (e.g., /tmp/agent-diagram-$(date +%s).png). Never use descriptive names.
• After mmdc runs successfully, output a markdown image (![description](path)) on its own line.
• Choose an appropriate diagram type for the data (sequence, flowchart, class, state, er, gantt, etc.).
• Include a title when it adds clarity.
• If no diagrammable data exists in the recent context, inform the user.