feat: add password protection UI and fix launch flow

- Password management UI in settings (set/change/remove password)
- Shield icon on play button for protected identities
- Interactive password popup on launch with inline error display
- Fix: re-throw password errors instead of falling to local tokens
- Fix: password popup properly cleans up on success/cancel
- Fix: expose updatePasswordShieldIcon for cross-module access

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

GUI/js/launcher.js

@@ -292,6 +292,25 @@ export async function launch() {
       }
       resetPlayButton();
 
+      if (result.usernameTaken) {
+        // Username reserved by another player
+        if (window.LauncherUI && window.LauncherUI.showError) {
+          window.LauncherUI.showError('This username is reserved by another player. Please change your player name in Identity settings.');
+        } else {
+          showNotification('This username is reserved by another player. Please change your player name.', 'error');
+        }
+        return;
+      }
+
+      if (result.passwordRequired) {
+        // UUID has a password — show interactive password dialog
+        const launchResult = await promptForPasswordAndLaunch(playerName, javaPath, gpuPreference);
+        if (launchResult && launchResult.success) {
+          if (window.electronAPI.minimizeWindow) setTimeout(() => { window.electronAPI.minimizeWindow(); }, 500);
+        }
+        return;
+      }
+
       if (result.success) {
         if (window.electronAPI.minimizeWindow) {
           setTimeout(() => {
@@ -354,6 +373,177 @@ export async function launch() {
   }
 }
 
+function promptForPasswordAndLaunch(playerName, javaPath, gpuPreference) {
+  return new Promise((resolve) => {
+    // Remove any existing password prompt
+    const existing = document.querySelector('.custom-confirm-modal');
+    if (existing) existing.remove();
+
+    const overlay = document.createElement('div');
+    overlay.className = 'custom-confirm-modal';
+    overlay.style.cssText = `
+      position: fixed;
+      top: 0;
+      left: 0;
+      right: 0;
+      bottom: 0;
+      background: rgba(0, 0, 0, 0.8);
+      backdrop-filter: blur(4px);
+      z-index: 20000;
+      display: flex;
+      align-items: center;
+      justify-content: center;
+    `;
+
+    const dialog = document.createElement('div');
+    dialog.style.cssText = `
+      background: #1f2937;
+      border-radius: 12px;
+      padding: 0;
+      min-width: 380px;
+      max-width: 420px;
+      box-shadow: 0 20px 40px rgba(0, 0, 0, 0.6);
+      border: 1px solid rgba(255, 255, 255, 0.1);
+    `;
+
+    dialog.innerHTML = `
+      <div style="padding: 20px 24px; border-bottom: 1px solid rgba(255,255,255,0.1);">
+        <div style="display: flex; align-items: center; gap: 10px; color: #f59e0b;">
+          <i class="fas fa-lock" style="font-size: 20px;"></i>
+          <h3 style="margin: 0; font-size: 1.1rem; font-weight: 600; color: #e5e7eb;">Password Required</h3>
+        </div>
+      </div>
+      <div style="padding: 20px 24px;">
+        <p style="margin: 0 0 12px 0; color: #9ca3af; font-size: 0.9rem; line-height: 1.5;">This identity is password-protected. Enter your password to continue.</p>
+        <div id="pwErrorMsg" style="display: none; margin-bottom: 12px; padding: 8px 12px; background: rgba(239,68,68,0.15); border: 1px solid rgba(239,68,68,0.3); border-radius: 6px; color: #f87171; font-size: 0.85rem;"></div>
+        <input type="password" id="launchPasswordInput" style="
+          width: 100%;
+          box-sizing: border-box;
+          padding: 10px 14px;
+          background: rgba(0,0,0,0.3);
+          border: 1px solid rgba(255,255,255,0.15);
+          border-radius: 8px;
+          color: #e5e7eb;
+          font-size: 0.95rem;
+          outline: none;
+        " placeholder="Password" autofocus />
+      </div>
+      <div style="padding: 16px 24px; display: flex; gap: 10px; justify-content: flex-end; border-top: 1px solid rgba(255,255,255,0.1);">
+        <button id="pwCancelBtn" style="
+          background: transparent;
+          color: #9ca3af;
+          border: 1px solid rgba(156,163,175,0.3);
+          padding: 9px 18px;
+          border-radius: 6px;
+          cursor: pointer;
+          font-size: 0.9rem;
+        ">Cancel</button>
+        <button id="pwConfirmBtn" style="
+          background: #f59e0b;
+          color: #000;
+          border: none;
+          padding: 9px 18px;
+          border-radius: 6px;
+          cursor: pointer;
+          font-weight: 600;
+          font-size: 0.9rem;
+        ">Login</button>
+      </div>
+    `;
+
+    overlay.appendChild(dialog);
+    document.body.appendChild(overlay);
+
+    const input = overlay.querySelector('#launchPasswordInput');
+    const confirmBtn = overlay.querySelector('#pwConfirmBtn');
+    const cancelBtn = overlay.querySelector('#pwCancelBtn');
+    const errorMsg = overlay.querySelector('#pwErrorMsg');
+
+    let busy = false;
+
+    const close = (result) => {
+      overlay.remove();
+      isDownloading = false;
+      if (window.LauncherUI) window.LauncherUI.hideProgress();
+      resetPlayButton();
+      resolve(result);
+    };
+
+    const showError = (msg) => {
+      errorMsg.textContent = msg;
+      errorMsg.style.display = 'block';
+      input.style.borderColor = 'rgba(239,68,68,0.5)';
+      input.value = '';
+      input.focus();
+    };
+
+    const tryLogin = async () => {
+      const password = input.value;
+      if (!password) {
+        showError('Please enter your password.');
+        return;
+      }
+      if (busy) return;
+      busy = true;
+
+      // Show loading state
+      confirmBtn.disabled = true;
+      confirmBtn.textContent = 'Logging in...';
+      errorMsg.style.display = 'none';
+      input.style.borderColor = 'rgba(255,255,255,0.15)';
+
+      try {
+        if (window.LauncherUI) window.LauncherUI.showProgress();
+        isDownloading = true;
+        const playBtn = document.getElementById('play-btn');
+        const playText = playBtn?.querySelector('.play-text');
+        if (playBtn) { playBtn.disabled = true; }
+        if (playText) { playText.textContent = 'LAUNCHING...'; }
+
+        const result = await window.electronAPI.launchGameWithPassword(playerName, javaPath, '', gpuPreference, password);
+
+        if (result.success) {
+          overlay.remove();
+          isDownloading = false;
+          if (window.LauncherUI) window.LauncherUI.hideProgress();
+          resetPlayButton();
+          resolve(result);
+          return;
+        }
+
+        // Wrong password
+        if (result.passwordRequired) {
+          showError(result.error || 'Incorrect password. Please try again.');
+        } else {
+          showError(result.error || 'Launch failed.');
+        }
+
+        isDownloading = false;
+        if (window.LauncherUI) window.LauncherUI.hideProgress();
+        resetPlayButton();
+      } catch (err) {
+        showError(err.message || 'An error occurred.');
+        isDownloading = false;
+        if (window.LauncherUI) window.LauncherUI.hideProgress();
+        resetPlayButton();
+      } finally {
+        busy = false;
+        confirmBtn.disabled = false;
+        confirmBtn.textContent = 'Login';
+      }
+    };
+
+    confirmBtn.addEventListener('click', tryLogin);
+    cancelBtn.addEventListener('click', () => close(null));
+    input.addEventListener('keydown', (e) => {
+      if (e.key === 'Enter') tryLogin();
+      if (e.key === 'Escape') close(null);
+    });
+
+    setTimeout(() => input.focus(), 100);
+  });
+}
+
 function showCustomConfirm(message, title, onConfirm, onCancel = null, confirmText, cancelText) {
   // Apply defaults with i18n support
   title = title || (window.i18n ? window.i18n.t('confirm.defaultTitle') : 'Confirm Action');
@@ -712,7 +902,7 @@ async function loadIdentities() {
   }
 }
 
-function renderIdentityList(mappings, currentUsername) {
+async function renderIdentityList(mappings, currentUsername) {
   const list = document.getElementById('identityList');
   if (!list) return;
 
@@ -721,13 +911,31 @@ function renderIdentityList(mappings, currentUsername) {
     return;
   }
 
-  list.innerHTML = mappings.map(m => {
+  // Check password status for all identities in parallel
+  const statusChecks = mappings.map(async m => {
+    try {
+      if (m.uuid && window.electronAPI?.checkPasswordStatus) {
+        const s = await window.electronAPI.checkPasswordStatus(m.uuid);
+        return s?.hasPassword || false;
+      }
+    } catch {}
+    return false;
+  });
+  const statuses = await Promise.all(statusChecks);
+
+  list.innerHTML = mappings.map((m, i) => {
     const safe = escapeHtml(m.username);
+    const isActive = m.username === currentUsername;
+    const hasPassword = statuses[i];
+    const pwBadge = hasPassword
+      ? '<span class="pw-badge locked"><i class="fas fa-lock"></i></span>'
+      : '<span class="pw-badge unlocked"><i class="fas fa-unlock"></i></span>';
     return `
-    <div class="identity-item ${m.username === currentUsername ? 'active' : ''}"
+    <div class="identity-item ${isActive ? 'active' : ''}"
          onclick="switchIdentity('${safe.replace(/'/g, "&#39;")}')">
         <span>${safe}</span>
-        ${m.username === currentUsername ? '<i class="fas fa-check ml-auto"></i>' : ''}
+        ${pwBadge}
+        ${isActive ? '<i class="fas fa-check" style="margin-left:4px;"></i>' : ''}
     </div>
   `;
   }).join('');
@@ -774,6 +982,9 @@ window.switchIdentity = async (username) => {
     if (settingsInput) settingsInput.value = username;
     if (window.loadCurrentUuid) window.loadCurrentUuid();
 
+    // Update password shield icon for new identity
+    if (window.updatePasswordShieldIcon) window.updatePasswordShieldIcon();
+
   } catch (error) {
     console.error('Failed to switch identity:', error);
   }