diff --git a/packages/agent-runtime/src/__tests__/prompts-schema-handling.test.ts b/packages/agent-runtime/src/__tests__/prompts-schema-handling.test.ts
index c6fe9dd058..9fd64c73fc 100644
--- a/packages/agent-runtime/src/__tests__/prompts-schema-handling.test.ts
+++ b/packages/agent-runtime/src/__tests__/prompts-schema-handling.test.ts
@@ -202,7 +202,7 @@ describe('Schema handling error recovery', () => {
       expect(description).toContain('content')
     })
 
-    test('buildToolDescription preserves MCP params when schema is represented as allOf', () => {
+    test('buildToolDescription preserves MCP params from converted schema', () => {
       const mcpSchema = convertJsonSchemaToZod({
         type: 'object',
         properties: {
@@ -221,8 +221,8 @@ describe('Schema handling error recovery', () => {
 
       expect(description).toContain('greet__greet')
       expect(description).toContain('Params: {')
-      expect(description).toContain('allOf')
       expect(description).toContain('name')
+      expect(description).toContain('cb_easp')
       expect(description).not.toContain('Params: None')
     })
 
diff --git a/packages/agent-runtime/src/templates/prompts.ts b/packages/agent-runtime/src/templates/prompts.ts
index d4e96faa03..459736941d 100644
--- a/packages/agent-runtime/src/templates/prompts.ts
+++ b/packages/agent-runtime/src/templates/prompts.ts
@@ -16,7 +16,11 @@ function ensureJsonSchemaCompatible(schema: z.ZodType): z.ZodType {
     return schema
   } catch {
     const fallback = z.object({}).passthrough()
-    return schema.description ? fallback.describe(schema.description) : fallback
+    try {
+      return schema.description ? fallback.describe(schema.description) : fallback
+    } catch {
+      return fallback
+    }
   }
 }
 
diff --git a/packages/agent-runtime/src/tools/prompts.ts b/packages/agent-runtime/src/tools/prompts.ts
index 9465a3c456..25ecfccdda 100644
--- a/packages/agent-runtime/src/tools/prompts.ts
+++ b/packages/agent-runtime/src/tools/prompts.ts
@@ -43,7 +43,11 @@ function ensureJsonSchemaCompatible(schema: z.ZodType): z.ZodType {
     return schema
   } catch {
     const fallback = z.object({}).passthrough()
-    return schema.description ? fallback.describe(schema.description) : fallback
+    try {
+      return schema.description ? fallback.describe(schema.description) : fallback
+    } catch {
+      return fallback
+    }
   }
 }