fix: detect puck reappearance in waitReconnect for Android Chrome (#129)

On Android Chrome, openDevice() requires a user gesture so autoConnect()
never succeeds after a firmware update reboot. waitReconnect() would time
out and show an error even though the update had applied successfully.

Now waitReconnect() also polls navigator.usb.getDevices() after the puck
disconnects. If the device reappears there but can't be auto-opened, it
returns "appeared" instead of false. runUpdate() treats "appeared" as
success and shows "Update applied — the puck is back. Tap Connect to
reconnect." rather than the bogus 40 s timeout failure message.

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

docs/index.html

@@ -1588,11 +1588,24 @@ function updateFwGate(){
     +"drive it mounts. Every update after that happens right here.";
   for(const c of document.querySelectorAll(".fwupcard")) c.classList.toggle("gated", !ok);
 }
-// after the apply-reboot: resolved true once the panel has reconnected AND received a fresh status blob
+// after the apply-reboot: resolved once the puck is back.
+// Returns true if the panel auto-reconnected and received a fresh status blob (desktop), "appeared"
+// if the puck is visible in getDevices() but openDevice() couldn't be called without a user gesture
+// (Android Chrome), or false on timeout.
 async function waitReconnect(t0,ms){
   const deadline=Date.now()+ms;
+  // seenGone: the puck must disconnect before we can declare it "back".  It is often already gone
+  // by the time this runs (fwupRun sent the reboot command and returned), so initialise from dev.
+  let seenGone=!dev;
   while(Date.now()<deadline){
     if(dev && window._lastBlobTs>t0) return true;
+    if(!dev) seenGone=true;
+    if(seenGone && !dev){
+      try{
+        const ds=await navigator.usb.getDevices();
+        if(ds.some(x=>USB_FILTERS.some(f=>f.vendorId===x.vendorId))) return "appeared";
+      }catch(_e){}
+    }
     await dfuSleep(400);
   }
   return false;
@@ -1621,9 +1634,14 @@ async function runUpdate(title, confirmText, getImage){
     await fwupRun(image);
     modalStage("Applying on the puck",null);
     $("#updDetail").textContent="the puck goes dark ~5 s while the new firmware is written, then re-enumerates";
-    if(await waitReconnect(t0,40000)){
+    const result=await waitReconnect(t0,40000);
+    if(result===true){
       const nb=blobBuildId(lastP);
       modalDone(true,"Update applied — the puck is back and running build "+(nb||"?")+(oldBuild&&nb!==oldBuild?" (was "+oldBuild+")":""));
+    }else if(result==="appeared"){
+      // The puck re-enumerated but the browser couldn't auto-open it (requires a user gesture on
+      // Android Chrome).  The update landed — the user just needs to tap Connect.
+      modalDone(true,"Update applied — the puck is back. Tap Connect to reconnect.");
     }else{
       modalDone(false,"The update was sent and armed, but the puck didn't reconnect within 40 s. Unplug/replug it. "
         +"If it mounts as a UF2BOOT drive, drag the .uf2 onto the drive to recover — the bootloader is intact.");