diff --git a/Examples/cs/cspidcontroller/cs_pid_controller.bngl b/Examples/cs/cspidcontroller/cs_pid_controller.bngl
index 23847ab9..38906937 100644
--- a/Examples/cs/cspidcontroller/cs_pid_controller.bngl
+++ b/Examples/cs/cspidcontroller/cs_pid_controller.bngl
@@ -78,8 +78,7 @@ begin functions
                    P_term() + I_term() + D_term(),0)
     
     # Disturbance function (step at t=disturb_time)
-    # Hack: use a very steep sigmoid to approximate step function
-    Disturb_rate() = disturb_mag / (1 + exp(-10*(t - disturb_time)))
+    Disturb_rate() = if(t > disturb_time, disturb_mag, 0)
 end functions
 
 begin reaction rules
diff --git a/scripts/generate-manifest.js b/scripts/generate-manifest.js
index a9f81c6f..720f5574 100644
--- a/scripts/generate-manifest.js
+++ b/scripts/generate-manifest.js
@@ -1,6 +1,6 @@
 const fs = require('fs');
 const path = require('path');
-const { listModelFiles } = require('./utils');
+const { listModelFiles, listModelFilesAsync } = require('./utils');
 
 const SEARCH_ROOTS = ['Published', 'Examples', 'Tutorials'];
 
@@ -143,31 +143,38 @@ function buildEntry(root, metadata, metadataFile, modelFile, isCollection) {
   };
 }
 
-function main() {
+async function main() {
   const { root, output } = parseArgs(process.argv.slice(2));
   const metadataFiles = SEARCH_ROOTS.flatMap(searchRoot => listMetadataFiles(path.join(root, searchRoot)));
-  const manifestEntries = [];
 
-  for (const metadataFile of metadataFiles) {
-    const metadata = parseMetadataYaml(fs.readFileSync(metadataFile, 'utf8'));
-    const modelFiles = listModelFiles(path.dirname(metadataFile));
-    if (modelFiles.length === 0) continue;
+  const entryPromises = metadataFiles.map(async (metadataFile) => {
+    const content = await fs.promises.readFile(metadataFile, 'utf8');
+    const metadata = parseMetadataYaml(content);
+    const modelFiles = await listModelFilesAsync(path.dirname(metadataFile));
+
+    if (modelFiles.length === 0) return [];
 
     const isCollection = modelFiles.length > 1 || Boolean(metadata.collection);
-    for (const modelFile of modelFiles) {
-      manifestEntries.push(buildEntry(root, metadata, metadataFile, modelFile, isCollection));
-    }
-  }
+    return modelFiles.map(modelFile =>
+      buildEntry(root, metadata, metadataFile, modelFile, isCollection)
+    );
+  });
+
+  const manifestEntries = (await Promise.all(entryPromises)).flat();
 
   manifestEntries.sort((left, right) => left.id.localeCompare(right.id));
-  fs.writeFileSync(output, JSON.stringify(manifestEntries, null, 2));
+  await fs.promises.writeFile(output, JSON.stringify(manifestEntries, null, 2));
   console.log(`Generated ${manifestEntries.length} manifest entries at ${output}`);
 }
 
 if (require.main === module) {
-  main();
+  main().catch((err) => {
+    console.error(err);
+    process.exit(1);
+  });
 }
 
 module.exports = {
   buildEntry,
+  parseMetadataYaml,
 };
\ No newline at end of file
diff --git a/scripts/generate-manifest.test.js b/scripts/generate-manifest.test.js
index eeef5520..2cc080a1 100644
--- a/scripts/generate-manifest.test.js
+++ b/scripts/generate-manifest.test.js
@@ -1,7 +1,7 @@
 const test = require('node:test');
 const assert = require('node:assert');
 const path = require('path');
-const { buildEntry } = require('./generate-manifest.js');
+const { buildEntry, parseMetadataYaml } = require('./generate-manifest.js');
 
 test('buildEntry', async (t) => {
   await t.test('handles a single model with full metadata', () => {
@@ -94,3 +94,109 @@ test('buildEntry', async (t) => {
     assert.strictEqual(entry.visible, false);
   });
 });
+
+test('parseMetadataYaml', async (t) => {
+  await t.test('parses basic key-value pairs', () => {
+    const yaml = `
+id: my-model
+name: "My Model"
+description: A test model
+featured: true
+count: 42
+    `;
+    const result = parseMetadataYaml(yaml);
+    assert.deepStrictEqual(result, {
+      id: 'my-model',
+      name: 'My Model',
+      description: 'A test model',
+      featured: true,
+      count: 42
+    });
+  });
+
+  await t.test('ignores empty lines and comments', () => {
+    const yaml = `
+# This is a comment
+id: model-1
+
+# Another comment
+
+name: test
+    `;
+    const result = parseMetadataYaml(yaml);
+    assert.deepStrictEqual(result, {
+      id: 'model-1',
+      name: 'test'
+    });
+  });
+
+  await t.test('parses list arrays (tags)', () => {
+    const yaml = `
+id: model-tags
+tags:
+  - biology
+  - physics
+  - chemistry
+    `;
+    const result = parseMetadataYaml(yaml);
+    assert.deepStrictEqual(result, {
+      id: 'model-tags',
+      tags: ['biology', 'physics', 'chemistry']
+    });
+  });
+
+  await t.test('parses nested objects', () => {
+    const yaml = `
+id: nested-model
+compatibility:
+  bng2_compatible: true
+  simulation_methods: [ode, ssa]
+source:
+  origin: published
+  original_repository: "http://example.com"
+    `;
+    const result = parseMetadataYaml(yaml);
+    assert.deepStrictEqual(result, {
+      id: 'nested-model',
+      compatibility: {
+        bng2_compatible: true,
+        simulation_methods: ['ode', 'ssa']
+      },
+      source: {
+        origin: 'published',
+        original_repository: 'http://example.com'
+      }
+    });
+  });
+
+  await t.test('parses deeply nested objects', () => {
+    const yaml = `
+a:
+  b:
+    c:
+      d: value
+    `;
+    const result = parseMetadataYaml(yaml);
+    assert.deepStrictEqual(result, {
+      a: {
+        b: {
+          c: {
+            d: 'value'
+          }
+        }
+      }
+    });
+  });
+
+  await t.test('handles empty tags array', () => {
+    const yaml = `
+id: empty-tags
+tags:
+    `;
+    const result = parseMetadataYaml(yaml);
+    assert.deepStrictEqual(result, {
+      id: 'empty-tags',
+      tags: []
+    });
+  });
+});
diff --git a/scripts/utils.js b/scripts/utils.js
index d0f4c2ce..e64c34a9 100644
--- a/scripts/utils.js
+++ b/scripts/utils.js
@@ -7,6 +7,15 @@ function listModelFiles(dir) {
     .sort();
 }
 
+async function listModelFilesAsync(dir) {
+  const entries = await fs.promises.readdir(dir, { withFileTypes: true });
+  return entries
+    .filter((entry) => entry.isFile() && entry.name.endsWith('.bngl'))
+    .map((entry) => entry.name)
+    .sort();
+}
+
 module.exports = {
-  listModelFiles
+  listModelFiles,
+  listModelFilesAsync
 };
diff --git a/scripts/utils.test.js b/scripts/utils.test.js
new file mode 100644
index 00000000..8f6fc911
--- /dev/null
+++ b/scripts/utils.test.js
@@ -0,0 +1,52 @@
+const test = require('node:test');
+const assert = require('node:assert');
+const fs = require('fs');
+const os = require('os');
+const path = require('path');
+const { listModelFiles } = require('./utils.js');
+
+test('utils.js', async (t) => {
+  let tmpDir;
+
+  t.beforeEach(() => {
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'bionetgen-utils-test-'));
+  });
+
+  t.afterEach(() => {
+    if (tmpDir) {
+      fs.rmSync(tmpDir, { recursive: true, force: true });
+    }
+  });
+
+  await t.test('listModelFiles returns only .bngl files in alphabetical order', () => {
+    fs.writeFileSync(path.join(tmpDir, 'model2.bngl'), 'content');
+    fs.writeFileSync(path.join(tmpDir, 'model1.bngl'), 'content');
+    fs.writeFileSync(path.join(tmpDir, 'model3.bngl'), 'content');
+
+    const files = listModelFiles(tmpDir);
+    assert.deepStrictEqual(files, ['model1.bngl', 'model2.bngl', 'model3.bngl']);
+  });
+
+  await t.test('listModelFiles ignores directories even if named with .bngl extension', () => {
+    fs.writeFileSync(path.join(tmpDir, 'model1.bngl'), 'content');
+    fs.mkdirSync(path.join(tmpDir, 'dir.bngl'));
+    fs.mkdirSync(path.join(tmpDir, 'other-dir'));
+
+    const files = listModelFiles(tmpDir);
+    assert.deepStrictEqual(files, ['model1.bngl']);
+  });
+
+  await t.test('listModelFiles ignores files with other extensions', () => {
+    fs.writeFileSync(path.join(tmpDir, 'model1.bngl'), 'content');
+    fs.writeFileSync(path.join(tmpDir, 'data.txt'), 'content');
+    fs.writeFileSync(path.join(tmpDir, 'model2.xml'), 'content');
+
+    const files = listModelFiles(tmpDir);
+    assert.deepStrictEqual(files, ['model1.bngl']);
+  });
+
+  await t.test('listModelFiles returns empty array for empty directory', () => {
+    const files = listModelFiles(tmpDir);
+    assert.deepStrictEqual(files, []);
+  });
+});
diff --git a/scripts/validate-metadata.js b/scripts/validate-metadata.js
index 6cb8645c..355f7e87 100644
--- a/scripts/validate-metadata.js
+++ b/scripts/validate-metadata.js
@@ -93,7 +93,7 @@ function parseMetadataYaml(content) {
     const trimmed = rawLine.trim();
 
     if (trimmed.startsWith('- ')) {
-      const currentPath = stack.map((entry) => entry.key).join('.');
+      const currentPath = stack.length > 0 ? stack[stack.length - 1].path : '';
       const listValue = parseScalar(trimmed.slice(2));
       if (currentPath === 'tags') {
         result.tags = Array.isArray(result.tags) ? result.tags : [];
@@ -111,10 +111,10 @@ function parseMetadataYaml(content) {
 
     const key = trimmed.slice(0, separator).trim();
     const rawValue = trimmed.slice(separator + 1);
-    const dottedPath = [...stack.map((entry) => entry.key), key].join('.');
+    const dottedPath = stack.length > 0 ? stack[stack.length - 1].path + '.' + key : key;
 
     if (!rawValue.trim()) {
-      stack.push({ key, indent });
+      stack.push({ key, indent, path: dottedPath });
       if (dottedPath === 'tags') {
         result.tags = Array.isArray(result.tags) ? result.tags : [];
       }
@@ -275,4 +275,5 @@ module.exports = {
   parseScalar,
   validateMetadataFile,
   parseMetadataYaml,
+  listMetadataFiles,
 };
\ No newline at end of file
diff --git a/scripts/validate-metadata.test.js b/scripts/validate-metadata.test.js
index f161308d..f63a422b 100644
--- a/scripts/validate-metadata.test.js
+++ b/scripts/validate-metadata.test.js
@@ -1,6 +1,6 @@
 const test = require('node:test');
 const assert = require('node:assert');
-const { parseMetadataYaml } = require('./validate-metadata.js');
+const { parseMetadataYaml, listMetadataFiles } = require('./validate-metadata.js');
 
 test('parseMetadataYaml', async (t) => {
   await t.test('parses basic key-value pairs', () => {
@@ -107,3 +107,11 @@ tags:
     });
   });
 });
+
+test('listMetadataFiles', async (t) => {
+  await t.test('returns empty array for non-existent directory', () => {
+    const nonExistentPath = '/path/that/does/not/exist/for/sure/12345';
+    const result = listMetadataFiles(nonExistentPath);
+    assert.deepStrictEqual(result, []);
+  });
+});
diff --git a/tests/validate-metadata.test.js b/tests/validate-metadata.test.js
index 748d276e..f0aaa47a 100644
--- a/tests/validate-metadata.test.js
+++ b/tests/validate-metadata.test.js
@@ -57,6 +57,91 @@ test('valid metadata file passes validation without errors', () => {
   });
 });
 
+test('invalid enum values for expectEnum fields add errors', () => {
+  withTempDir((tempDir) => {
+    const metadataFile = path.join(tempDir, 'metadata.yaml');
+
+    // Test with wrong types (e.g. number, boolean, null instead of string)
+    const invalidTypeYaml = `
+id: "test-model"
+name: "Test Model"
+description: "A test model"
+tags: []
+category: 123
+compatibility:
+  bng2_compatible: true
+  uses_compartments: false
+  uses_energy: false
+  uses_functions: true
+  nfsim_compatible: false
+  simulation_methods: [ode]
+source:
+  origin: true
+  original_repository: "repo"
+playground:
+  visible: true
+  gallery_category: "Test"
+  featured: false
+  difficulty: null
+collection:
+  type: 456
+  parent_model: "test-model"
+  variant_key: "test"
+  count: 2
+`;
+    fs.writeFileSync(metadataFile, invalidTypeYaml);
+    fs.writeFileSync(path.join(tempDir, 'README.md'), '# Test Model');
+    fs.writeFileSync(path.join(tempDir, 'model1.bngl'), '');
+    fs.writeFileSync(path.join(tempDir, 'model2.bngl'), '');
+
+    let errors = [];
+    validateMetadataFile(metadataFile, errors);
+
+    assert.ok(errors.some(e => e.includes('invalid category (123)')), 'Should report invalid category type');
+    assert.ok(errors.some(e => e.includes('invalid source.origin (true)')), 'Should report invalid origin type');
+    assert.ok(errors.some(e => e.includes('invalid playground.difficulty (null)')), 'Should report invalid difficulty type');
+    assert.ok(errors.some(e => e.includes('invalid collection.type (456)')), 'Should report invalid collection type');
+
+    // Test with string values not in the allowed sets
+    const invalidStringYaml = `
+id: "test-model"
+name: "Test Model"
+description: "A test model"
+tags: []
+category: "not-a-real-category"
+compatibility:
+  bng2_compatible: true
+  uses_compartments: false
+  uses_energy: false
+  uses_functions: true
+  nfsim_compatible: false
+  simulation_methods: [ode]
+source:
+  origin: "fake-origin"
+  original_repository: "repo"
+playground:
+  visible: true
+  gallery_category: "Test"
+  featured: false
+  difficulty: "extremely-hard"
+collection:
+  type: "unknown-collection-type"
+  parent_model: "test-model"
+  variant_key: "test"
+  count: 2
+`;
+    fs.writeFileSync(metadataFile, invalidStringYaml);
+
+    errors = [];
+    validateMetadataFile(metadataFile, errors);
+
+    assert.ok(errors.some(e => e.includes('invalid category ("not-a-real-category")')), 'Should report invalid category string');
+    assert.ok(errors.some(e => e.includes('invalid source.origin ("fake-origin")')), 'Should report invalid origin string');
+    assert.ok(errors.some(e => e.includes('invalid playground.difficulty ("extremely-hard")')), 'Should report invalid difficulty string');
+    assert.ok(errors.some(e => e.includes('invalid collection.type ("unknown-collection-type")')), 'Should report invalid collection type string');
+  });
+});
+
 test('missing README.md adds error', () => {
   withTempDir((tempDir) => {
     const metadataFile = path.join(tempDir, 'metadata.yaml');