git:20261001.707fde7 to git:20261001.3e811b0

4 added, 4 removed. Audit A to A.

---

name: drawio-png

description: Read the draw.io diagram embedded in a *.drawio.png (also .drawio / .drawio.svg) as text — vertices, edges, and the custom attributes behind the picture (kind, port, traced, …). Use whenever a task asks what a diagram says, who calls whom in an architecture/deployment picture, or to check a diagram against the code — instead of eyeballing the image.

allowed-tools: Bash(.claude/skills/drawio-png/drawio.py:*)

---

# drawio-png

A `*.drawio.png` is a picture **and** the full draw.io source: the XML sits in a PNG text

chunk. Read that, never the pixels — labels in the image omit the custom attributes that

carry the semantics (e.g. `traced="yes"` on edges, `port`/`tech` on containers).

```sh

.claude/skills/drawio-png/drawio.py <file> # vertices + edges + attributes (graph)

.claude/skills/drawio-png/drawio.py json <file> # same, JSON — pipe to jq

.claude/skills/drawio-png/drawio.py xml <file> # full decoded mxGraph XML (styles, geometry)

```

Diagrams in this repo: `petclinic-backend/docs/Deployment.drawio.png`,

`petclinic-backend/docs/ConceptualModel.drawio.png`.

## What the script unwraps (so you don't redo it)

- PNG chunks `tEXt` / `zTXt` / `iTXt`; keyword is `mxfile` (draw.io) or a bare `mxGraphModel`

(`ConceptualModel.drawio.png` uses this keyword, yet its payload is still an `<mxfile>`).

- Payload is URL-encoded; a `<diagram>` body may further be base64 → raw deflate → URL-encoded.

- Custom properties: draw.io wraps the cell in `<object>`/`<UserObject>` and **moves `id` and

`label` onto the wrapper**; the inner `<mxCell>` has no id. The script merges them.

- Multi-page files print one block per page.

- Labels parented to an edge (`*`, `1`, …) are its multiplicities: printed on the edge, at

the end they sit at (`Owner --> Pet [*]` = many pets per owner), not as vertices.

## A diagram is a claim, not evidence

The picture shows what someone drew. Before answering "only X calls Y", grep the code for

the other side — base URLs, ports, `RestClient`/`WebClient`, MCP clients, `.mcp.json`,

- compose files — and report drift. Here, `Deployment.drawio.png` has no chatbot, while

- `petclinic-chatbot` calls the backend (MCP `/mcp`, and polls `/api/specialties/feed`).

- `DeploymentDiagramTest` compares the drawing with traces both ways, but only the traces of

- the browser suites, and the chatbot runs no OTel agent — so it can never notice that gap.

+ compose files — and report drift. `DeploymentDiagramTest` compares the drawing with traces

+ both ways, but only the traces of the browser suites: an edge marked `traced="no"` — the

+ chatbot's, which runs no OTel agent — is checked by nothing. It once vanished from the

+ picture for a month (`a57d5e18`) with every test green.

## Guardrail code

`petclinic-backend/src/test/java/victor/training/petclinic/guardrail/DrawioDiagram.java`

does the same decoding in Java for tests; keep both in step if the format handling changes.