Add homepage quick join flow

app/static/js/play/app.js

@@ -87,6 +87,7 @@ export class PlayApp {
     this.displayBoardSize = 640;
     this.squareSize = 80;
     this.dpr = Math.max(1, window.devicePixelRatio || 1);
+    this.urlJoinConsumed = false;
 
     this.loadPieceImages();
     this.installControls();
@@ -127,6 +128,7 @@ export class PlayApp {
 
   installSocket() {
     this.socket = createWSClient({
+      onServerReady: () => this.consumeJoinCodeFromUrl(),
       onGameStarted: handleGameStarted,
       onP2Connected: handleP2Connected,
       onGameCreated: handleCodeGameCreated,
@@ -170,16 +172,7 @@ export class PlayApp {
     });
 
     this.joinBtn.addEventListener("click", () => {
-      const code = this.joinInput.value.trim().toUpperCase();
-      if (!code) {
-        this.showModal("Join game", "Enter a game code first.", [
-          { label: "OK" },
-        ]);
-        return;
-      }
-      this.gameCode = code;
-      this.socket.emit("join_code_game", { code });
-      this.setLobbyStatus("Joining game...");
+      this.joinCode(this.joinInput.value);
     });
 
     this.copyCodeBtn.addEventListener("click", async () => {
@@ -358,6 +351,40 @@ export class PlayApp {
     });
   }
 
+  joinCode(rawCode) {
+    const code = String(rawCode || "").trim().toUpperCase();
+    if (!code) {
+      this.showModal("Join game", "Enter a game code first.", [
+        { label: "OK" },
+      ]);
+      return false;
+    }
+
+    this.gameCode = code;
+    this.joinInput.value = code;
+    this.socket.emit("join_code_game", { code });
+    this.setLobbyStatus("Joining game...");
+    return true;
+  }
+
+  consumeJoinCodeFromUrl() {
+    if (this.urlJoinConsumed) {
+      return;
+    }
+
+    const url = new URL(window.location.href);
+    const code = url.searchParams.get("code");
+    if (!code) {
+      return;
+    }
+
+    this.urlJoinConsumed = true;
+    url.searchParams.delete("code");
+    const nextUrl = `${url.pathname}${url.search}${url.hash}`;
+    window.history.replaceState({}, "", nextUrl);
+    this.joinCode(code);
+  }
+
   onCodeCreated(data) {
     this.gameCode = data.code;
     this.codeEl.textContent = data.code;