Add sheet-music-server example

Demo MCP App showcasing ABC notation rendering and audio playback with:
- Server-side ABC notation validation
- Built-in audio player with play/pause and loop controls
- Sheet music visualization using abcjs library

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

examples/sheet-music-server/src/mcp-app.ts

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+/**
+ * @file Sheet Music App - renders ABC notation with abcjs and provides audio playback
+ */
+import { App } from "@modelcontextprotocol/ext-apps";
+import ABCJS from "abcjs";
+import "abcjs/abcjs-audio.css";
+import "./global.css";
+import "./mcp-app.css";
+
+const log = {
+  info: console.log.bind(console, "[APP]"),
+  error: console.error.bind(console, "[APP]"),
+};
+
+// State management
+interface AppState {
+  visualObj: ABCJS.TuneObject[] | null;
+  synthControl: ABCJS.SynthObjectController | null;
+}
+
+const state: AppState = {
+  visualObj: null,
+  synthControl: null,
+};
+
+// DOM element references
+const mainEl = document.querySelector(".main") as HTMLElement;
+const statusEl = document.getElementById("status")!;
+const sheetMusicEl = document.getElementById("sheet-music")!;
+const audioControlsEl = document.getElementById("audio-controls")!;
+
+/**
+ * Updates the status display.
+ */
+function setStatus(text: string, isError = false): void {
+  statusEl.textContent = text;
+  statusEl.classList.toggle("error", isError);
+}
+
+/**
+ * Renders ABC notation to sheet music and sets up audio playback
+ */
+async function renderAbc(abcNotation: string): Promise<void> {
+  try {
+    setStatus("Rendering...");
+
+    // Clear previous content
+    sheetMusicEl.innerHTML = "";
+    audioControlsEl.innerHTML = "";
+
+    // Render the sheet music visually
+    state.visualObj = ABCJS.renderAbc(sheetMusicEl, abcNotation, {
+      responsive: "resize",
+      add_classes: true,
+    });
+
+    if (!state.visualObj || state.visualObj.length === 0) {
+      throw new Error("Failed to parse music notation");
+    }
+
+    if (!ABCJS.synth.supportsAudio()) {
+      throw new Error("Audio not supported in this browser");
+    }
+
+    // Create synth controller with UI controls
+    state.synthControl = new ABCJS.synth.SynthController();
+    state.synthControl.load(audioControlsEl, null, {
+      displayLoop: true,
+      // displayRestart: true,
+      displayPlay: true,
+      displayProgress: true,
+      // displayWarp: true,
+    });
+
+    // Connect synth to the rendered tune
+    await state.synthControl.setTune(state.visualObj[0], false, {});
+
+    setStatus("Ready to play!");
+  } catch (error) {
+    log.error("Render error:", error);
+    setStatus(`Error: ${(error as Error).message}`, true);
+    audioControlsEl.innerHTML = "";
+  }
+}
+
+// Create app instance
+const app = new App({ name: "Sheet Music App", version: "1.0.0" });
+
+// Handle tool input - receives ABC notation from the host
+app.ontoolinput = (params) => {
+  log.info("Received tool input:", params);
+
+  const abcNotation = params.arguments?.abcNotation as string | undefined;
+
+  if (abcNotation) {
+    renderAbc(abcNotation);
+  } else {
+    setStatus("No ABC notation provided", true);
+  }
+};
+
+// Error handler
+app.onerror = log.error;
+
+app.onhostcontextchanged = (params) => {
+  if (params.safeAreaInsets) {
+    mainEl.style.paddingTop = `${params.safeAreaInsets.top}px`;
+    mainEl.style.paddingRight = `${params.safeAreaInsets.right}px`;
+    mainEl.style.paddingBottom = `${params.safeAreaInsets.bottom}px`;
+    mainEl.style.paddingLeft = `${params.safeAreaInsets.left}px`;
+  }
+};
+
+// Connect to host
+app.connect().then(() => {
+  const ctx = app.getHostContext();
+  if (ctx) {
+    app.onhostcontextchanged(ctx);
+  }
+});