feat(pi-family): quietBoot — hide the shared rootfs' branded boot chatter

The generic arm64 image prints another product's banner/motd/login line
during boot, before guestSetup can re-brand the guest. Boards with
quietBoot show a neutral '[Velxio] Booting <label> (Linux guest)...'
progress line (dots every 4 s) while boot detection and the prompt-gated
upload still run underneath; the shell is revealed (already re-branded)
right before the auto-run command, so the user's first visible output is
their own program.

frontend/src/lib/proBoardRegistry.ts

@@ -71,6 +71,12 @@ export interface ProBoardDef {
    *  this line executed, so a single click on Run boots, uploads and
    *  starts the user's script (piFamily boards only). */
   autoRun?: string;
+  /** Suppress the guest's boot chatter in the terminal (piFamily boards
+   *  only): the shared rootfs prints another product's banner/motd during
+   *  boot, before guestSetup can re-brand it. With quietBoot the terminal
+   *  shows a neutral Velxio boot-progress line instead and reveals the
+   *  shell right before the auto-run command executes. */
+  quietBoot?: boolean;
   /** Canvas renderer. Receives the placed board's props; return a React node.
    *  When omitted, the canvas renders `<tag id=... style=absolute@x,y>`. */
   render?: (props: { id: string; x: number; y: number; running: boolean }) => React.ReactNode;

frontend/src/simulation/RaspberryPi3Bridge.ts

@@ -75,6 +75,15 @@ export class RaspberryPi3Bridge {
   private socket: WebSocket | null = null;
   private _connected = false;
   private _booted = false;
+  /** quietBoot (ProBoardDef): while true, guest serial output is withheld
+   * from onSerialData (boot detection still runs) and a neutral Velxio
+   * progress line + dots show instead. The run path calls setQuiet(false)
+   * to reveal the shell right before the script starts. */
+  quietBootDefault = false;
+  /** Board label for the quiet-boot progress line. */
+  quietBootLabel = '';
+  private _quiet = false;
+  private _quietTimer: ReturnType<typeof setInterval> | null = null;
   /** Rolling, escape-stripped tail of recent guest output, used to detect the
    * boot-complete marker and shell prompts for flow-controlled sends. */
   private _serialTail = '';
@@ -110,6 +119,12 @@ export class RaspberryPi3Bridge {
       this.onConnected?.();
       // Tell the backend which Pi family member to boot.
       this._send({ type: 'start_pi', data: { board: this.boardKind } });
+      if (this.quietBootDefault) {
+        this._quiet = true;
+        const label = this.quietBootLabel || this.boardKind;
+        this._emitLocal(`[Velxio] Booting ${label} (Linux guest)`);
+        this._quietTimer = setInterval(() => this._emitLocal('.', false), 4000);
+      }
     };
 
     socket.onmessage = (event: MessageEvent) => {
@@ -123,7 +138,9 @@ export class RaspberryPi3Bridge {
       switch (msg.type) {
         case 'serial_output': {
           const text = (msg.data.data as string) ?? '';
-          if (this.onSerialData) {
+          // quietBoot: keep observing (boot marker + prompt waiters drive
+          // guestSetup and the upload) but withhold the branded chatter.
+          if (!this._quiet && this.onSerialData) {
             for (const ch of text) this.onSerialData(ch);
           }
           this._observeSerial(text);
@@ -183,11 +200,37 @@ export class RaspberryPi3Bridge {
   private _resetBootState(): void {
     this._booted = false;
     this._serialTail = '';
+    this._quiet = false;
+    if (this._quietTimer) {
+      clearInterval(this._quietTimer);
+      this._quietTimer = null;
+    }
     const waiters = this._promptWaiters;
     this._promptWaiters = [];
     for (const w of waiters) w();
   }
 
+  /** Feed locally-generated status text to the serial consumers. */
+  private _emitLocal(text: string, newline = true): void {
+    if (!this.onSerialData) return;
+    const chunk = newline ? `\r\n${text}` : text;
+    for (const ch of chunk) this.onSerialData(ch);
+  }
+
+  /** Reveal (or re-hide) the guest's serial stream. Turning quiet off ends
+   * the progress dots and prints a ready line. */
+  setQuiet(on: boolean): void {
+    if (this._quiet === on) return;
+    this._quiet = on;
+    if (!on) {
+      if (this._quietTimer) {
+        clearInterval(this._quietTimer);
+        this._quietTimer = null;
+      }
+      this._emitLocal(' ready.\r\n');
+    }
+  }
+
   /** Send a byte to the Pi's ttyAMA0 (user serial) */
   sendSerialByte(byte: number): void {
     this._send({ type: 'serial_input', data: { bytes: [byte] } });

frontend/src/store/useSimulatorStore.ts

@@ -777,8 +777,14 @@ export async function piSyncAndRunScript(boardId: string, boardKind: string): Pr
     .getState()
     .getGroupFiles(groupId)
     .map((f) => ({ path: `${home}/${f.name}`, content: f.content }));
-  const { uploadFilesToPi } = await import('../utils/piUpload');
-  await uploadFilesToPi(bridge, files);
+  try {
+    const { uploadFilesToPi } = await import('../utils/piUpload');
+    await uploadFilesToPi(bridge, files);
+  } finally {
+    // Reveal the shell (ends quietBoot) right before the script starts, so
+    // the user's first visible output is their own program.
+    bridge.setQuiet(false);
+  }
   const cmd = proDef?.autoRun ?? `python3 ${home}/script.py`;
   bridge.sendSerialText(cmd.endsWith('\n') ? cmd : cmd + '\n');
 }
@@ -1259,6 +1265,11 @@ export const useSimulatorStore = create<SimulatorState>((set, get) => {
 
       if (isPiBoardKind(boardKind)) {
         const bridge = new RaspberryPi3Bridge(id, boardKind);
+        const piDef = getProBoard(boardKind);
+        if (piDef?.quietBoot) {
+          bridge.quietBootDefault = true;
+          bridge.quietBootLabel = piDef.label;
+        }
         bridge.onSerialData = (ch: string) => {
           serialCallback(ch);
           // Cross-board routing now handled by Interconnect (see bind below).