diff --git a/src/manifest.ts b/src/manifest.ts
index 5f75e8c..d362c25 100644
--- a/src/manifest.ts
+++ b/src/manifest.ts
@@ -171,7 +171,11 @@ function primitiveComposition(schema: Record<string, unknown> | undefined): Reco
     return constraints;
   });
   if (mapped.some((branch) => branch === undefined)) return undefined;
-  return { [key]: mapped };
+  return {
+    ...(typeof schema.type === 'string' ? { type: schema.type } : {}),
+    ...(Array.isArray(schema.enum) ? { enum: schema.enum } : {}),
+    [key]: mapped,
+  };
 }
 
 /**
diff --git a/test/parameter-composition-root.test.ts b/test/parameter-composition-root.test.ts
new file mode 100644
index 0000000..513465f
--- /dev/null
+++ b/test/parameter-composition-root.test.ts
@@ -0,0 +1,28 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import type { OpenAPIV3 } from 'openapi-types';
+import { init } from '../vendor/forge/index.js';
+import { buildManifest } from '../src/manifest.js';
+const { compileOutputValidator } = await import(new URL('../runtime/server.mjs', import.meta.url).href) as {
+  compileOutputValidator: (schema: unknown) => (value: unknown) => boolean;
+};
+
+for (const location of ['path', 'query', 'header', 'cookie']) {
+  test(`primitive ${location} compositions retain sibling type and enum constraints`, async () => {
+    const doc = { openapi: '3.1.0', info: { title: 'Compositions', version: '1' }, components: { schemas: {} },
+      paths: { [location === 'path' ? '/x/{v}' : '/x']: { get: { operationId: 'x', parameters: [{ name: 'v', in: location, required: true, schema: {
+        type: 'integer', enum: [2, 'safe'], anyOf: [{ type: 'integer' }, { type: 'string' }],
+      } }], responses: { '200': { description: 'OK' } } } } },
+    } as unknown as OpenAPIV3.Document;
+    await init(doc);
+    const tool = buildManifest(doc).tools[0]!;
+    const arg = tool.args.find(a => a.location === location)!;
+    assert.equal(arg.schema.type, 'integer');
+    assert.deepEqual(arg.schema.enum, [2, 'safe']);
+    const validate = compileOutputValidator(JSON.parse(JSON.stringify(tool.inputSchema)));
+    const args = { v: 2 };
+    assert.equal(validate(args), true);
+    assert.equal(validate({ ...args, [arg.name]: 3 }), false);
+    assert.equal(validate({ ...args, [arg.name]: 'safe' }), false);
+  });
+}