fix(library): validate saved library paths

src/main/library-path-config.ts

@@ -19,10 +19,10 @@ function isPlainObject(value: unknown): value is Record<string, unknown> {
 }
 
 /**
- * Normalize an administrator-supplied DLC_DIR and accept it only when it
- * already names a directory. Invalid overrides must not shadow config.json.
+ * Normalize a configured library path and accept it only when it already
+ * names a directory.
  */
-export function normalizeExplicitLibraryPath(rawPath?: string): string | undefined {
+export function normalizeExistingLibraryDirectory(rawPath?: string): string | undefined {
     const candidate = (rawPath || '').trim();
     if (!candidate) return undefined;
 
@@ -33,6 +33,22 @@ export function normalizeExplicitLibraryPath(rawPath?: string): string | undefin
     }
 }
 
+/**
+ * Apply the prepared library-path contract to the Python child environment.
+ * Starting from a copy of process.env means an invalid or stale parent value
+ * must be removed explicitly when config.json owns the path.
+ */
+export function applyLibraryPathToPythonEnvironment(
+    environment: Record<string, string>,
+    preparation: LibraryPathPreparation,
+): void {
+    if (preparation.environmentDlcDir) {
+        environment.DLC_DIR = preparation.environmentDlcDir;
+    } else {
+        delete environment.DLC_DIR;
+    }
+}
+
 /**
  * Prepare the library path contract for the Python backend.
  *
@@ -46,7 +62,7 @@ export function prepareLibraryPathForPython(
     resolvedDlcDir: string,
     explicitDlcDir?: string,
 ): LibraryPathPreparation {
-    const override = normalizeExplicitLibraryPath(explicitDlcDir);
+    const override = normalizeExistingLibraryDirectory(explicitDlcDir);
     if (override) {
         return {
             status: 'explicit-override',
@@ -76,7 +92,13 @@ export function prepareLibraryPathForPython(
 
         const configured = config.dlc_dir;
         if (typeof configured === 'string' && configured.trim()) {
-            return { status: 'configured' };
+            if (normalizeExistingLibraryDirectory(configured)) {
+                return { status: 'configured' };
+            }
+            return {
+                status: 'invalid-config',
+                error: 'config.json dlc_dir is not an existing directory',
+            };
         }
         if (configured !== undefined && configured !== null && configured !== '') {
             return {

src/main/python.ts

@@ -11,7 +11,11 @@ import * as net from 'net';
 import * as os from 'os';
 import { getActiveSoundfontPath, getDesktopConfig } from './soundfont-manager';
 import { isDebugEnabled } from './debug-log';
-import { normalizeExplicitLibraryPath, prepareLibraryPathForPython } from './library-path-config';
+import {
+    applyLibraryPathToPythonEnvironment,
+    normalizeExistingLibraryDirectory,
+    prepareLibraryPathForPython,
+} from './library-path-config';
 
 let pythonProcess: ChildProcess | null = null;
 // A backend that is being *gracefully* stopped (SIGTERM sent, async SIGKILL
@@ -424,7 +428,7 @@ function getPluginsDir(): string {
     return pluginsDir;
 }
 
-function getDLCDir(explicitDlcDir = normalizeExplicitLibraryPath(process.env.DLC_DIR)): string {
+function getDLCDir(explicitDlcDir = normalizeExistingLibraryDirectory(process.env.DLC_DIR)): string {
     if (explicitDlcDir) return explicitDlcDir;
 
     // Read from shared config
@@ -497,7 +501,7 @@ export async function startPython(): Promise<void> {
     }
     serverPort = await findPort(PREFERRED_PORT);
     const configDir = getConfigDir();
-    const explicitDlcDir = normalizeExplicitLibraryPath(process.env.DLC_DIR);
+    const explicitDlcDir = normalizeExistingLibraryDirectory(process.env.DLC_DIR);
     const dlcDir = getDLCDir(explicitDlcDir);
     // Ensure the resolved library folder exists before the server starts. The
     // Python side only seeds starter content (and scans) when DLC_DIR.is_dir()
@@ -582,13 +586,9 @@ export async function startPython(): Promise<void> {
             : path.join(__dirname, '..', '..', 'resources', 'bin') + path.delimiter
         ) + (process.env.PATH || ''),
     };
-    if (libraryPath.environmentDlcDir) {
-        pythonEnv.DLC_DIR = libraryPath.environmentDlcDir;
-    } else {
-        // `...process.env` may carry an empty/invalid value. Do not let it
-        // shadow config.json in the normal dynamic-settings path.
-        delete pythonEnv.DLC_DIR;
-    }
+    // `...process.env` may carry an empty/invalid value. Do not let it shadow
+    // config.json in the normal dynamic-settings path.
+    applyLibraryPathToPythonEnvironment(pythonEnv, libraryPath);
 
     // Debug mode: raise the Slopsmith server's log level and tee its
     // structured logs to a file. lib/logging_setup.py reads LOG_LEVEL and