diff --git a/src/utils/schema-sanitizer.ts b/src/utils/schema-sanitizer.ts
index 5a2d798e..0639f14e 100644
--- a/src/utils/schema-sanitizer.ts
+++ b/src/utils/schema-sanitizer.ts
@@ -216,6 +216,7 @@ export function sanitizeSchemaForOpenAICompat(schema: unknown): Record<string, u
 
   const schemaWithoutEnum = { ...record };
   delete schemaWithoutEnum.enum;
+  delete schemaWithoutEnum.const;
 
   if (Array.isArray(record.enum)) {
     const filteredEnum = record.enum.filter((value) => schemaAllowsValue(schemaWithoutEnum, value));
diff --git a/tests/unit/utils/schema-sanitizer.test.ts b/tests/unit/utils/schema-sanitizer.test.ts
new file mode 100644
index 00000000..baf3290b
--- /dev/null
+++ b/tests/unit/utils/schema-sanitizer.test.ts
@@ -0,0 +1,85 @@
+import { describe, expect, it } from 'bun:test';
+
+import { normalizeSchemaForOpenAI } from '../../../src/utils/schema-sanitizer';
+
+describe('normalizeSchemaForOpenAI', () => {
+  it('strips incompatible keywords and enforces strict object schemas', () => {
+    const result = normalizeSchemaForOpenAI({
+      type: 'object',
+      properties: {
+        query: { type: 'string', pattern: '^[a-z]+$', minLength: 3 },
+        limit: { type: 'integer', minimum: 1 },
+      },
+      required: ['query', 'missing'],
+      additionalProperties: true,
+      default: { query: 'docs' },
+    });
+
+    expect(result).toEqual({
+      type: 'object',
+      properties: {
+        query: { type: 'string' },
+        limit: { type: 'integer' },
+      },
+      required: ['query'],
+      additionalProperties: false,
+    });
+  });
+
+  it('drops enum and const values that no longer match the schema type', () => {
+    const result = normalizeSchemaForOpenAI({
+      type: 'string',
+      enum: ['ok', 1, null],
+      const: 1,
+    });
+
+    expect(result).toEqual({
+      type: 'string',
+      enum: ['ok'],
+    });
+  });
+
+  it('normalizes nested combinators and arrays recursively', () => {
+    const result = normalizeSchemaForOpenAI({
+      anyOf: [
+        {
+          type: 'object',
+          properties: {
+            image: {
+              type: 'array',
+              items: {
+                type: 'object',
+                properties: {
+                  url: { type: 'string', format: 'uri' },
+                },
+              },
+            },
+          },
+        },
+      ],
+    });
+
+    expect(result).toEqual({
+      anyOf: [
+        {
+          type: 'object',
+          properties: {
+            image: {
+              type: 'array',
+              items: {
+                type: 'object',
+                properties: {
+                  url: { type: 'string' },
+                },
+                required: [],
+                additionalProperties: false,
+              },
+            },
+          },
+          required: [],
+          additionalProperties: false,
+        },
+      ],
+    });
+  });
+});