fix(update): resolve template path when updating to a different base model (#1059)

Version-tab updates reused the current version's folder, so updating a LoRA
to a version with a different base model (e.g. Illustrious -> Anima) ignored
the download path template and landed in the old version's directory.

When the target version's base model differs from the current local version
and a path template is configured, re-resolve the template under the same
model root. The backend keeps an explicitly provided root when
use_save_dir_as_root is set, so regular downloads still use the default root.

static/js/api/baseModelApi.js

@@ -1233,7 +1233,7 @@ export class BaseModelApiClient {
         }
     }
 
-    async downloadModel(modelId, versionId, modelRoot, relativePath, useDefaultPaths = false, downloadId, source = null, fileParams = null) {
+    async downloadModel(modelId, versionId, modelRoot, relativePath, useDefaultPaths = false, downloadId, source = null, fileParams = null, useSaveDirAsRoot = false) {
         try {
             const response = await fetch(DOWNLOAD_ENDPOINTS.download, {
                 method: 'POST',
@@ -1244,6 +1244,7 @@ export class BaseModelApiClient {
                     model_root: modelRoot,
                     relative_path: relativePath,
                     use_default_paths: useDefaultPaths,
+                    use_save_dir_as_root: useSaveDirAsRoot,
                     download_id: downloadId,
                     ...(source ? { source } : {}),
                     ...(fileParams ? { file_params: fileParams } : {})

static/js/components/shared/ModelVersionsTab.js

@@ -1307,15 +1307,41 @@ export function initVersionsTab({
         });
     }
 
-    async function resolveDownloadPathFromCurrentVersion() {
+    function getCurrentInLibraryVersion() {
         if (!normalizedCurrentVersionId || !controller.record?.versions) {
             return null;
         }
-
-        const currentVersion = controller.record.versions.find(
+        return controller.record.versions.find(
             v => v.versionId === normalizedCurrentVersionId && v.isInLibrary && v.filePath
-        );
-        if (!currentVersion?.filePath) {
+        ) || null;
+    }
+
+    function getDownloadPathTemplate() {
+        try {
+            const singularType = modelType.replace(/s$/, '');
+            const templates = state.global?.settings?.download_path_templates;
+            return (templates && templates[singularType]) || '';
+        } catch (error) {
+            return '';
+        }
+    }
+
+    function shouldResolveTemplatePath(targetVersion, pathInfo) {
+        if (!getDownloadPathTemplate() || !pathInfo?.modelRoot) {
+            return false;
+        }
+        const currentVersion = getCurrentInLibraryVersion();
+        const currentBase = normalizeBaseModelName(currentVersion?.baseModel);
+        const targetBase = normalizeBaseModelName(targetVersion?.baseModel);
+        if (!currentBase || !targetBase || currentBase === targetBase) {
+            return false;
+        }
+        return true;
+    }
+
+    async function resolveDownloadPathFromCurrentVersion() {
+        const currentVersion = getCurrentInLibraryVersion();
+        if (!currentVersion) {
             return null;
         }
 
@@ -1372,10 +1398,13 @@ export function initVersionsTab({
 
         try {
             const pathInfo = await resolveDownloadPathFromCurrentVersion();
+            const resolveTemplatePath = shouldResolveTemplatePath(version, pathInfo);
             const success = await downloadManager.downloadVersionWithDefaults(modelType, modelId, versionId, {
                 versionName: version.name || `#${version.versionId}`,
                 modelRoot: pathInfo?.modelRoot || '',
-                targetFolder: pathInfo?.targetFolder || '',
+                targetFolder: resolveTemplatePath ? '' : (pathInfo?.targetFolder || ''),
+                useDefaultPaths: resolveTemplatePath ? true : null,
+                useSaveDirAsRoot: resolveTemplatePath,
             });
 
             if (success) {

static/js/managers/DownloadManager.js

@@ -912,6 +912,7 @@ export class DownloadManager {
         modelRoot = '',
         targetFolder = '',
         useDefaultPaths = false,
+        useSaveDirAsRoot = false,
         source = null,
         fileParams = null,
         closeModal = false,
@@ -923,7 +924,7 @@ export class DownloadManager {
         }
 
         const displayName = versionName || `#${versionId}`;
-        const retryParams = { modelId, versionId, versionName, modelRoot, targetFolder, useDefaultPaths, source, fileParams, closeModal: false };
+        const retryParams = { modelId, versionId, versionName, modelRoot, targetFolder, useDefaultPaths, useSaveDirAsRoot, source, fileParams, closeModal: false };
         let ws = null;
         let updateProgress = () => { };
         let cancelled = false;
@@ -995,7 +996,8 @@ export class DownloadManager {
                 useDefaultPaths,
                 downloadId,
                 source,
-                fileParams
+                fileParams,
+                useSaveDirAsRoot
             );
 
             if (cancelled) {
@@ -1809,7 +1811,9 @@ export class DownloadManager {
         versionName = '', 
         source = null,
         modelRoot = '',
-        targetFolder = ''
+        targetFolder = '',
+        useDefaultPaths = null,
+        useSaveDirAsRoot = false
     } = {}) {
         console.warn('[download] downloadVersionWithDefaults: NO fileParams will be sent — backend will always use primary file. '
             + 'modelType=%s, modelId=%s, versionId=%s, versionName="%s"',
@@ -1824,14 +1828,14 @@ export class DownloadManager {
         this.modelId = modelId ? modelId.toString() : null;
         this.source = source;
 
-        const useDefaultPaths = !modelRoot;
         return this.executeDownloadWithProgress({
             modelId,
             versionId,
             versionName,
             modelRoot: modelRoot || '',
             targetFolder: targetFolder || '',
-            useDefaultPaths,
+            useDefaultPaths: useDefaultPaths ?? !modelRoot,
+            useSaveDirAsRoot,
             source,
             closeModal: false,
         });