fix(library): apply saved path without restart

tests/library-path-config.test.js

@@ -0,0 +1,92 @@
+'use strict';
+
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const os = require('node:os');
+const path = require('node:path');
+const { loadTs, ROOT } = require('./_load-ts');
+
+const {
+    prepareLibraryPathForPython,
+} = loadTs('src/main/library-path-config.ts');
+
+function tmpConfigDir() {
+    return fs.mkdtempSync(path.join(os.tmpdir(), 'feedback-library-path-'));
+}
+
+test('normal desktop startup bootstraps the fallback into config instead of DLC_DIR', () => {
+    const configDir = tmpConfigDir();
+    const result = prepareLibraryPathForPython(configDir, 'C:\\Music\\fee[dB]ack');
+
+    assert.deepEqual(result, { status: 'bootstrapped' });
+    assert.deepEqual(
+        JSON.parse(fs.readFileSync(path.join(configDir, 'config.json'), 'utf8')),
+        { dlc_dir: 'C:\\Music\\fee[dB]ack' },
+    );
+    assert.equal(result.environmentDlcDir, undefined);
+});
+
+test('bootstrap merges the fallback into an existing config without losing settings', () => {
+    const configDir = tmpConfigDir();
+    const configFile = path.join(configDir, 'config.json');
+    fs.writeFileSync(configFile, JSON.stringify({ master_difficulty: 75 }));
+
+    const result = prepareLibraryPathForPython(configDir, 'D:\\Songs');
+
+    assert.equal(result.status, 'bootstrapped');
+    assert.deepEqual(
+        JSON.parse(fs.readFileSync(configFile, 'utf8')),
+        { master_difficulty: 75, dlc_dir: 'D:\\Songs' },
+    );
+});
+
+test('an existing saved library stays config-owned and can change between scans', () => {
+    const configDir = tmpConfigDir();
+    const configFile = path.join(configDir, 'config.json');
+    fs.writeFileSync(configFile, JSON.stringify({ dlc_dir: 'D:\\Saved Songs' }));
+
+    const result = prepareLibraryPathForPython(configDir, 'C:\\Default Songs');
+
+    assert.deepEqual(result, { status: 'configured' });
+    assert.deepEqual(
+        JSON.parse(fs.readFileSync(configFile, 'utf8')),
+        { dlc_dir: 'D:\\Saved Songs' },
+    );
+    assert.equal(result.environmentDlcDir, undefined);
+});
+
+test('an explicit valid DLC_DIR remains an environment override', () => {
+    const configDir = tmpConfigDir();
+    const result = prepareLibraryPathForPython(
+        configDir,
+        'C:\\Default Songs',
+        ' D:\\Managed Songs ',
+    );
+
+    assert.deepEqual(result, {
+        status: 'explicit-override',
+        environmentDlcDir: 'D:\\Managed Songs',
+    });
+    assert.equal(fs.existsSync(path.join(configDir, 'config.json')), false);
+});
+
+test('a corrupt config is never overwritten during bootstrap', () => {
+    const configDir = tmpConfigDir();
+    const configFile = path.join(configDir, 'config.json');
+    fs.writeFileSync(configFile, '{broken');
+
+    const result = prepareLibraryPathForPython(configDir, 'C:\\Default Songs');
+
+    assert.equal(result.status, 'invalid-config');
+    assert.match(result.error, /JSON/);
+    assert.equal(fs.readFileSync(configFile, 'utf8'), '{broken');
+});
+
+test('python startup does not pin its resolved fallback as DLC_DIR', () => {
+    const source = fs.readFileSync(path.join(ROOT, 'src', 'main', 'python.ts'), 'utf8');
+
+    assert.match(source, /prepareLibraryPathForPython\(configDir, dlcDir, explicitDlcDir\)/);
+    assert.doesNotMatch(source, /DLC_DIR:\s*dlcDir/);
+    assert.match(source, /delete pythonEnv\.DLC_DIR/);
+});