feat(mcp): add load_diagram tool to load .drawio files into the session (#893)

* feat(mcp): add load_diagram tool to load .drawio files into the session

Loading a file previously required the agent to read the file itself and
pass the entire XML through create_new_diagram - wasteful for large
diagrams and impossible for draw.io's compressed save format.

load_diagram takes a file path; the server reads it, decompresses any
compressed pages (base64 -> raw deflate -> URI-decode, per page), and
replaces the session document. The loaded XML is deliberately NOT marked
as seen by the edit gate: the model only supplied a path, so it must
call get_diagram once before editing.

* chore(mcp): version 0.2.3

* fix(mcp): report package.json version in the MCP handshake

The McpServer metadata version was a separate hardcoded string that
never matched the published version (stuck at 0.1.2, then 0.3.0 while
npm shipped 0.2.x). Read it from package.json at startup instead —
works from both src/ (tsx) and dist/ (published build).

packages/mcp-server/tests/load-diagram.test.ts

@@ -0,0 +1,126 @@
+/**
+ * Unit tests for load_diagram's file parsing (load-diagram.ts).
+ *
+ * A .drawio file stores each page's <mxGraphModel> either as plain XML or
+ * as draw.io's compressed default (encodeURIComponent → raw deflate →
+ * base64 text content). The loader must produce the canonical session
+ * shape: an <mxfile> whose every page is plain XML.
+ */
+
+import { deflateRawSync } from "node:zlib"
+import { DOMParser } from "linkedom"
+import { beforeAll, describe, expect, it } from "vitest"
+
+// Install the DOM polyfills exactly as index.ts does at runtime.
+beforeAll(() => {
+    ;(globalThis as any).DOMParser = DOMParser
+    class XMLSerializerPolyfill {
+        serializeToString(node: any): string {
+            if (node.outerHTML !== undefined) return node.outerHTML
+            if (node.documentElement) return node.documentElement.outerHTML
+            return ""
+        }
+    }
+    ;(globalThis as any).XMLSerializer = XMLSerializerPolyfill
+})
+
+import {
+    decompressPageContent,
+    parseDrawioFileContent,
+} from "../src/load-diagram.js"
+
+const MODEL_XML = `<mxGraphModel><root><mxCell id="0"/><mxCell id="1" parent="0"/><mxCell id="box1" value="Hello" style="rounded=0;" vertex="1" parent="1"><mxGeometry x="40" y="40" width="120" height="60" as="geometry"/></mxCell></root></mxGraphModel>`
+
+/** Compress a page body exactly the way draw.io does when saving. */
+function drawioCompress(xml: string): string {
+    return deflateRawSync(
+        Buffer.from(encodeURIComponent(xml), "utf-8"),
+    ).toString("base64")
+}
+
+const PLAIN_MXFILE = `<mxfile host="app.diagrams.net"><diagram id="p1" name="Page-1">${MODEL_XML}</diagram></mxfile>`
+const COMPRESSED_MXFILE = `<mxfile host="app.diagrams.net" compressed="true"><diagram id="p1" name="Page-1">${drawioCompress(MODEL_XML)}</diagram></mxfile>`
+
+describe("decompressPageContent", () => {
+    it("round-trips draw.io's compressed format", () => {
+        expect(decompressPageContent(drawioCompress(MODEL_XML))).toBe(MODEL_XML)
+    })
+
+    it("handles non-URI-encoded legacy payloads", () => {
+        const legacy = deflateRawSync(Buffer.from(MODEL_XML, "utf-8")).toString(
+            "base64",
+        )
+        expect(decompressPageContent(legacy)).toBe(MODEL_XML)
+    })
+
+    it("returns null for garbage", () => {
+        expect(decompressPageContent("not base64 deflate")).toBeNull()
+    })
+})
+
+describe("parseDrawioFileContent", () => {
+    it("passes a plain-XML mxfile through unchanged", () => {
+        const r = parseDrawioFileContent(PLAIN_MXFILE)
+        expect(r).toEqual({ ok: true, xml: PLAIN_MXFILE })
+    })
+
+    it("wraps a bare mxGraphModel into a one-page mxfile", () => {
+        const r = parseDrawioFileContent(MODEL_XML)
+        expect(r.ok).toBe(true)
+        if (r.ok) {
+            expect(r.xml).toContain("<mxfile")
+            expect(r.xml).toContain('value="Hello"')
+        }
+    })
+
+    it("decompresses a compressed mxfile into plain XML pages", () => {
+        const r = parseDrawioFileContent(COMPRESSED_MXFILE)
+        expect(r.ok).toBe(true)
+        if (r.ok) {
+            expect(r.xml).toContain("<mxGraphModel")
+            expect(r.xml).toContain('value="Hello"')
+            // The compressed blob must be gone.
+            expect(r.xml).not.toContain(drawioCompress(MODEL_XML))
+        }
+    })
+
+    it("decompresses only the compressed pages of a mixed file", () => {
+        const mixed = `<mxfile><diagram id="a" name="Plain">${MODEL_XML}</diagram><diagram id="b" name="Squeezed">${drawioCompress(MODEL_XML)}</diagram></mxfile>`
+        const r = parseDrawioFileContent(mixed)
+        expect(r.ok).toBe(true)
+        if (r.ok) {
+            const doc = new DOMParser().parseFromString(r.xml, "text/xml")
+            const diagrams = Array.from(
+                doc.querySelectorAll("diagram"),
+            ) as Element[]
+            expect(diagrams).toHaveLength(2)
+            for (const d of diagrams) {
+                expect(d.querySelector("mxGraphModel")).not.toBeNull()
+            }
+        }
+    })
+
+    it("keeps empty pages as-is", () => {
+        const withEmpty = `<mxfile><diagram id="a" name="Page-1">${MODEL_XML}</diagram><diagram id="b" name="Empty"></diagram></mxfile>`
+        const r = parseDrawioFileContent(withEmpty)
+        expect(r).toEqual({ ok: true, xml: withEmpty })
+    })
+
+    it("rejects empty files", () => {
+        const r = parseDrawioFileContent("   ")
+        expect(r.ok).toBe(false)
+    })
+
+    it("rejects non-drawio content", () => {
+        const r = parseDrawioFileContent("<svg><rect/></svg>")
+        expect(r.ok).toBe(false)
+        if (!r.ok) expect(r.error).toContain("Not a draw.io file")
+    })
+
+    it("rejects a page whose content is neither XML nor compressed", () => {
+        const bad = `<mxfile><diagram id="a" name="Broken">!!! not a diagram !!!</diagram></mxfile>`
+        const r = parseDrawioFileContent(bad)
+        expect(r.ok).toBe(false)
+        if (!r.ok) expect(r.error).toContain('"Broken"')
+    })
+})