fix(settings): reject checkpoints↔unet path overlap in extra folder paths with inline error UI

Changes:
- Backend: _validate_folder_paths() now checks checkpoints↔unet overlap
  within the same library using os.path.realpath() for symlink resolution
- Backend: set() calls _validate_folder_paths() for both folder_paths and
  extra_folder_paths before writing
- Backend: extracted _normalize_path_set() helper to eliminate duplicated
  normalization logic
- Frontend: inline error display with red border + error message below the
  conflicting input, no save triggered
- Frontend: path normalization (strip trailing slash, lowercase) in pre-check
  to reduce false negatives vs backend realpath
- Frontend: asymmetric error UX — message only on the user-edited side,
  red border on the pre-existing conflict side
- CSS: has-error styles with hardcoded rgba fallback for older browsers
- i18n: checkpointUnetOverlap + checkpointUnetOverlapInline keys added to
  all 10 locale files

locales/de.json

@@ -505,7 +505,9 @@
             "saveSuccess": "Zusätzliche Ordnerpfade aktualisiert. Neustart erforderlich, um Änderungen anzuwenden.",
             "saveError": "Fehler beim Aktualisieren der zusätzlichen Ordnerpfade: {message}",
             "validation": {
-                "duplicatePath": "Dieser Pfad ist bereits konfiguriert"
+                "duplicatePath": "Dieser Pfad ist bereits konfiguriert",
+                "checkpointUnetOverlap": "Derselbe Pfad kann nicht für Checkpoints und Diffusionsmodelle verwendet werden: {paths}",
+                "checkpointUnetOverlapInline": "Dieser Pfad wird bereits für einen anderen Modelltyp verwendet. Bitte verwenden Sie separate Ordner für Checkpoints und Diffusionsmodelle."
             }
         },
         "priorityTags": {

locales/en.json

@@ -505,7 +505,9 @@
       "saveSuccess": "Extra folder paths updated. Restart required to apply changes.",
       "saveError": "Failed to update extra folder paths: {message}",
       "validation": {
-        "duplicatePath": "This path is already configured"
+        "duplicatePath": "This path is already configured",
+        "checkpointUnetOverlap": "Cannot use the same path for both checkpoints and diffusion models: {paths}",
+        "checkpointUnetOverlapInline": "This path is also used for a different model type. Use separate folders for checkpoints and diffusion models."
       }
     },
     "priorityTags": {

locales/es.json

@@ -505,7 +505,9 @@
             "saveSuccess": "Rutas de carpetas adicionales actualizadas. Se requiere reinicio para aplicar los cambios.",
             "saveError": "Error al actualizar las rutas de carpetas adicionales: {message}",
             "validation": {
-                "duplicatePath": "Esta ruta ya está configurada"
+                "duplicatePath": "Esta ruta ya está configurada",
+                "checkpointUnetOverlap": "No se puede usar la misma ruta para checkpoints y modelos de difusión: {paths}",
+                "checkpointUnetOverlapInline": "Esta ruta ya se usa para otro tipo de modelo. Use carpetas separadas para checkpoints y modelos de difusión."
             }
         },
         "priorityTags": {

locales/fr.json

@@ -505,7 +505,9 @@
             "saveSuccess": "Chemins de dossiers supplémentaires mis à jour. Redémarrage requis pour appliquer les changements.",
             "saveError": "Échec de la mise à jour des chemins de dossiers supplémentaires: {message}",
             "validation": {
-                "duplicatePath": "Ce chemin est déjà configuré"
+                "duplicatePath": "Ce chemin est déjà configuré",
+                "checkpointUnetOverlap": "Impossible d'utiliser le même chemin pour les checkpoints et les modèles de diffusion : {paths}",
+                "checkpointUnetOverlapInline": "Ce chemin est déjà utilisé pour un autre type de modèle. Utilisez des dossiers séparés pour les checkpoints et les modèles de diffusion."
             }
         },
         "priorityTags": {

locales/he.json

@@ -505,7 +505,9 @@
             "saveSuccess": "נתיבי תיקיות נוספים עודכנו. נדרשת הפעלה מחדש כדי להחיל את השינויים.",
             "saveError": "נכשל בעדכון נתיבי תיקיות נוספים: {message}",
             "validation": {
-                "duplicatePath": "נתיב זה כבר מוגדר"
+                "duplicatePath": "נתיב זה כבר מוגדר",
+                "checkpointUnetOverlap": "לא ניתן להשתמש באותו נתיב עבור checkpoints ומודלי דיפוזיה: {paths}",
+                "checkpointUnetOverlapInline": "הנתיב הזה כבר נמצא בשימוש עבור סוג מודל אחר. יש להשתמש בתיקיות נפרדות עבור checkpoints ומודלי דיפוזיה."
             }
         },
         "priorityTags": {

locales/ja.json

@@ -505,7 +505,9 @@
             "saveSuccess": "追加フォルダーパスを更新しました。変更を適用するには再起動が必要です。",
             "saveError": "追加フォルダーパスの更新に失敗しました: {message}",
             "validation": {
-                "duplicatePath": "このパスはすでに設定されています"
+                "duplicatePath": "このパスはすでに設定されています",
+                "checkpointUnetOverlap": "checkpoints と diffusion models に同じパスは使用できません：{paths}",
+                "checkpointUnetOverlapInline": "このパスは別のモデルタイプですでに使用されています。checkpoints と diffusion models には別々のフォルダを使用してください。"
             }
         },
         "priorityTags": {

locales/ko.json

@@ -505,7 +505,9 @@
             "saveSuccess": "추가 폴다 경로가 업데이트되었습니다. 변경 사항을 적용하려면 재시작이 필요합니다.",
             "saveError": "추가 폴다 경로 업데이트 실패: {message}",
             "validation": {
-                "duplicatePath": "이 경로는 이미 구성되어 있습니다"
+                "duplicatePath": "이 경로는 이미 구성되어 있습니다",
+                "checkpointUnetOverlap": "checkpoints와 diffusion models에 동일한 경로를 사용할 수 없습니다: {paths}",
+                "checkpointUnetOverlapInline": "이 경로는 다른 모델 유형에 이미 사용 중입니다. checkpoints와 diffusion models에 별도의 폴더를 사용하세요."
             }
         },
         "priorityTags": {

locales/ru.json

@@ -505,7 +505,9 @@
             "saveSuccess": "Дополнительные пути к папкам обновлены. Требуется перезапуск для применения изменений.",
             "saveError": "Не удалось обновить дополнительные пути к папкам: {message}",
             "validation": {
-                "duplicatePath": "Этот путь уже настроен"
+                "duplicatePath": "Этот путь уже настроен",
+                "checkpointUnetOverlap": "Нельзя использовать один и тот же путь для checkpoints и diffusion models: {paths}",
+                "checkpointUnetOverlapInline": "Этот путь уже используется для другого типа модели. Используйте отдельные папки для checkpoints и diffusion models."
             }
         },
         "priorityTags": {

locales/zh-CN.json

@@ -505,7 +505,9 @@
             "saveSuccess": "额外文件夹路径已更新，需要重启才能生效。",
             "saveError": "更新额外文件夹路径失败：{message}",
             "validation": {
-                "duplicatePath": "此路径已配置"
+                "duplicatePath": "此路径已配置",
+                "checkpointUnetOverlap": "checkpoints 和 diffusion models 不能使用相同的路径：{paths}",
+                "checkpointUnetOverlapInline": "此路径已被用于另一种模型类型。请为 checkpoints 和 diffusion models 使用不同的文件夹。"
             }
         },
         "priorityTags": {

locales/zh-TW.json

@@ -505,7 +505,9 @@
             "saveSuccess": "額外資料夾路徑已更新，需要重啟才能生效。",
             "saveError": "更新額外資料夾路徑失敗：{message}",
             "validation": {
-                "duplicatePath": "此路徑已設定"
+                "duplicatePath": "此路徑已設定",
+                "checkpointUnetOverlap": "checkpoints 和 diffusion models 不能使用相同的路徑：{paths}",
+                "checkpointUnetOverlapInline": "此路徑已被用於另一種模型類型。請為 checkpoints 和 diffusion models 使用不同的資料夾。"
             }
         },
         "priorityTags": {

py/services/settings_manager.py

@@ -630,12 +630,37 @@ class SettingsManager:
 
         return False
 
+    @staticmethod
+    def _normalize_path_set(paths: Iterable[str]) -> set[str]:
+        """Normalize an iterable of paths for set-based overlap comparison.
+
+        Resolves symlinks via ``os.path.realpath`` when the path exists on disk,
+        then applies ``os.path.normcase`` + ``os.path.normpath`` for consistent
+        cross-platform comparison.  Non-string / empty entries are skipped.
+        """
+        result: set[str] = set()
+        for p in paths:
+            if not isinstance(p, str):
+                continue
+            stripped = p.strip()
+            if not stripped:
+                continue
+            if os.path.exists(stripped):
+                stripped = os.path.normpath(os.path.realpath(stripped))
+            result.add(os.path.normcase(stripped))
+        return result
+
     def _validate_folder_paths(
         self,
         library_name: str,
         folder_paths: Mapping[str, Iterable[str]],
     ) -> None:
-        """Ensure folder paths do not overlap with other libraries."""
+        """Ensure folder paths do not overlap with other libraries.
+
+        Also detects checkpoints ↔ unet path overlap within the same library
+        (including via symlink resolution), which is a configuration error since
+        these model types must use separate physical folders.
+        """
         libraries = self.settings.get("libraries", {})
         normalized_new: Dict[str, Dict[str, str]] = {}
         for key, values in folder_paths.items():
@@ -673,6 +698,22 @@ class SettingsManager:
                         f"Folder path(s) {collisions} already assigned to library '{other_name}'"
                     )
 
+        # Checkpoints ↔ unet overlap within the same library
+        ckpt_paths = folder_paths.get("checkpoints", []) or []
+        unet_paths = folder_paths.get("unet", []) or []
+        if ckpt_paths and unet_paths:
+            ckpt_real = self._normalize_path_set(ckpt_paths)
+            unet_real = self._normalize_path_set(unet_paths)
+            overlap = ckpt_real & unet_real
+            if overlap:
+                collisions = ", ".join(sorted(overlap))
+                raise ValueError(
+                    f"Path(s) {collisions} are configured for both "
+                    f"'checkpoints' and 'unet' (diffusion models). "
+                    f"These model types must use separate physical folders. "
+                    f"Please remove one of the conflicting entries."
+                )
+
     def _update_active_library_entry(
         self,
         *,
@@ -1547,8 +1588,12 @@ class SettingsManager:
             portable_switch_pending = True
             self._prepare_portable_switch(value)
         if key == "folder_paths" and isinstance(value, Mapping):
+            active_name = self.get_active_library_name()
+            self._validate_folder_paths(active_name, value)
             self._update_active_library_entry(folder_paths=value)  # type: ignore[arg-type]
         elif key == "extra_folder_paths" and isinstance(value, Mapping):
+            active_name = self.get_active_library_name()
+            self._validate_folder_paths(active_name, value)
             self._update_active_library_entry(extra_folder_paths=value)  # type: ignore[arg-type]
         elif key == "default_lora_root":
             self._update_active_library_entry(default_lora_root=str(value))

static/css/components/modal/settings-modal.css

@@ -1562,6 +1562,29 @@ input:checked + .toggle-slider:before {
     box-shadow: 0 0 0 2px rgba(var(--lora-accent-rgb, 79, 70, 229), 0.1);
 }
 
+.extra-folder-path-row .path-controls .extra-folder-path-input.has-error {
+    border-color: var(--lora-error);
+    background-color: rgba(220, 53, 69, 0.08);
+    background-color: rgba(from var(--lora-error) r g b / 0.08);
+}
+
+.extra-folder-path-row .path-controls .extra-folder-path-input.has-error:focus {
+    box-shadow: 0 0 0 2px rgba(220, 53, 69, 0.15);
+    box-shadow: 0 0 0 2px rgba(from var(--lora-error) r g b / 0.15);
+}
+
+.extra-folder-path-error {
+    color: var(--lora-error);
+    font-size: 0.8em;
+    margin-top: 4px;
+    line-height: 1.4;
+    display: none;
+}
+
+.extra-folder-path-error.visible {
+    display: block;
+}
+
 .extra-folder-path-row .path-controls .remove-path-btn {
     width: 32px;
     height: 32px;

static/js/managers/SettingsManager.js

@@ -1693,13 +1693,15 @@ export class SettingsManager {
                 <input type="text" class="extra-folder-path-input"
                        placeholder="${translate('settings.extraFolderPaths.pathPlaceholder', {}, '/path/to/models')}" value="${path}"
                        onblur="settingsManager.updateExtraFolderPaths('${modelType}')"
+                       onfocus="settingsManager.clearExtraFolderPathError(this)"
                        onkeydown="if(event.key === 'Enter') { this.blur(); }" />
                 <button type="button" class="remove-path-btn"
-                        onclick="this.parentElement.parentElement.remove(); settingsManager.updateExtraFolderPaths('${modelType}')"
+                        onclick="settingsManager.removeExtraFolderPathRow(this, '${modelType}')"
                         title="${translate('common.actions.delete', {}, 'Delete')}">
                     <i class="fas fa-times"></i>
                 </button>
             </div>
+            <div class="extra-folder-path-error"></div>
         `;
 
         container.appendChild(row);
@@ -1713,7 +1715,63 @@ export class SettingsManager {
         }
     }
 
+    clearExtraFolderPathError(input) {
+        input.classList.remove('has-error');
+        const row = input.closest('.extra-folder-path-row');
+        if (row) {
+            const errEl = row.querySelector('.extra-folder-path-error');
+            if (errEl) {
+                errEl.classList.remove('visible');
+                errEl.textContent = '';
+            }
+        }
+    }
+
+    _clearAllExtraFolderPathErrors() {
+        document.querySelectorAll('.extra-folder-path-input.has-error').forEach((input) => {
+            input.classList.remove('has-error');
+        });
+        document.querySelectorAll('.extra-folder-path-error.visible').forEach((el) => {
+            el.classList.remove('visible');
+            el.textContent = '';
+        });
+    }
+
+    _markExtraFolderPathsError(modelType, overlappingPaths, showMessage = false) {
+        const container = document.getElementById(`extraFolderPaths-${modelType}`);
+        if (!container) return;
+
+        const inputs = container.querySelectorAll('.extra-folder-path-input');
+        inputs.forEach((input) => {
+            const val = input.value.trim();
+            if (val && overlappingPaths.includes(val)) {
+                input.classList.add('has-error');
+                if (showMessage) {
+                    const row = input.closest('.extra-folder-path-row');
+                    if (row) {
+                        const errEl = row.querySelector('.extra-folder-path-error');
+                        if (errEl) {
+                            errEl.textContent = translate('settings.extraFolderPaths.validation.checkpointUnetOverlapInline', {}, 'This path is also used for a different model type. Use separate folders for checkpoints and diffusion models.');
+                            errEl.classList.add('visible');
+                        }
+                    }
+                }
+            }
+        });
+    }
+
+    removeExtraFolderPathRow(btn, modelType) {
+        const row = btn.closest('.extra-folder-path-row');
+        if (row) {
+            row.remove();
+            this.updateExtraFolderPaths(modelType);
+        }
+    }
+
     async updateExtraFolderPaths(changedModelType) {
+        // Clear previous errors
+        this._clearAllExtraFolderPathErrors();
+
         const extraFolderPaths = {};
 
         // Collect paths for all model types
@@ -1734,6 +1792,32 @@ export class SettingsManager {
             extraFolderPaths[modelType] = paths;
         });
 
+        // Client-side pre-check: checkpoints and unet must not share the same path.
+        // Normalise paths to reduce false negatives vs the backend's realpath + normcase.
+        const normalise = (p) => p.replace(/[/\\]+$/, '').toLowerCase();
+        const ckptSet = new Set((extraFolderPaths.checkpoints || []).map(normalise));
+        const unetSet = new Set((extraFolderPaths.unet || []).map(normalise));
+        const ckptOverlap = (extraFolderPaths.checkpoints || []).filter(p => p && unetSet.has(normalise(p)));
+        const unetOverlap = (extraFolderPaths.unet || []).filter(p => p && ckptSet.has(normalise(p)));
+        const hasOverlap = ckptOverlap.length > 0 || unetOverlap.length > 0;
+
+        if (hasOverlap) {
+            // Error message only on the side the user just edited.
+            // The other side gets red border only (passive conflict indicator).
+            if (changedModelType === 'checkpoints') {
+                this._markExtraFolderPathsError('checkpoints', ckptOverlap, true);
+                this._markExtraFolderPathsError('unet', unetOverlap, false);
+            } else if (changedModelType === 'unet') {
+                this._markExtraFolderPathsError('unet', unetOverlap, true);
+                this._markExtraFolderPathsError('checkpoints', ckptOverlap, false);
+            } else {
+                // Pre-existing conflict from direct config edit — mark both without messages
+                this._markExtraFolderPathsError('checkpoints', ckptOverlap, false);
+                this._markExtraFolderPathsError('unet', unetOverlap, false);
+            }
+            return;
+        }
+
         // Check if paths have actually changed
         const currentPaths = state.global.settings.extra_folder_paths || {};
         const pathsChanged = JSON.stringify(currentPaths) !== JSON.stringify(extraFolderPaths);