feat: Tier-1 Model Manager with Hot-Swapping, HF Download Engine, bug fixes, and test repairs

- Phase 4: Hugging Face Download Engine — streaming GGUF downloads with progress, cancellation, and managed-model storage
- Phase 5: Model Source Validation — source-mode compatibility, path/file validation, inline error UI with recovery guidance
- Hot-swap: stop runtime → update model_path → restart atomic command
- Model library: folder open, delete model file, local model management
- SettingsPage unified hub: local models list + HF search with 3-state action buttons
- Bug fixes: send button text restored (4 failing tests), reasoning-toggle aria-label, Rust warnings
- All 89 tests passing, cargo check clean

tauri-app/src/features/runtime/api.ts

@@ -1,6 +1,7 @@
 import { invoke } from "@tauri-apps/api/core";
 import { createDefaultRuntimeSnapshot, createRuntimeLifecycleResult } from "./runtime-utils";
 import type {
+  HuggingFaceDownloadProgress,
   ModelLibraryState,
   HuggingFaceModelResult,
   RuntimeConfig,
@@ -11,6 +12,7 @@ import type {
 } from "./types";
 
 const STORAGE_KEY = "forgelm_runtime_snapshot_v1";
+export const HUGGING_FACE_DOWNLOAD_EVENT = "hugging-face-download-progress";
 
 function canUseLocalStorage(): boolean {
   return typeof window !== "undefined" && typeof window.localStorage !== "undefined";
@@ -146,6 +148,62 @@ export async function searchHuggingFaceModels(query: string, token = ""): Promis
   });
 }
 
+export async function startHuggingFaceDownload(repo: string, fileName: string, token = ""): Promise<string> {
+  try {
+    return await invoke<string>("start_hugging_face_download_command", {
+      repo,
+      fileName,
+      token: token.trim() || null,
+    });
+  } catch (err) {
+    console.error("[api] startHuggingFaceDownload failed:", err);
+    throw err;
+  }
+}
+
+export async function cancelHuggingFaceDownload(downloadId: string): Promise<void> {
+  try {
+    return await invoke<void>("cancel_hugging_face_download_command", {
+      downloadId,
+    });
+  } catch (err) {
+    console.error("[api] cancelHuggingFaceDownload failed:", err);
+    throw err;
+  }
+}
+
 export async function getModelLibraryState(): Promise<ModelLibraryState> {
   return invoke<ModelLibraryState>("get_model_library_state_command");
 }
+
+/// Hot-swap: stop runtime → update model_path → restart.
+export async function swapModel(newModelPath: string): Promise<RuntimeSnapshot> {
+  try {
+    return await invoke<RuntimeSnapshot>("swap_model_command", { newModelPath });
+  } catch (err) {
+    console.error("[api] swapModel failed:", err);
+    throw err;
+  }
+}
+
+/// Delete a local .gguf model file from disk.
+export async function deleteModelFile(filePath: string): Promise<void> {
+  try {
+    return await invoke<void>("delete_model_file", { filePath });
+  } catch (err) {
+    console.error("[api] deleteModelFile failed:", err);
+    throw err;
+  }
+}
+
+/// Open the folder containing a model in the native file explorer.
+export async function openModelFolder(filePath: string): Promise<void> {
+  try {
+    return await invoke<void>("open_model_folder_command", { filePath });
+  } catch (err) {
+    console.error("[api] openModelFolder failed:", err);
+    throw err;
+  }
+}
+
+export type { HuggingFaceDownloadProgress };