fix(providers): normalize tool schemas for JSON Schema 2020-12 compliance (Bedrock/LiteLLM)

src/api/providers/__tests__/base-provider.spec.ts

@@ -140,7 +140,29 @@ describe("BaseProvider", () => {
 			expect(result.properties.level1.properties.level2.properties.level3.additionalProperties).toBe(false)
 		})
 
-		it("should convert nullable types to non-nullable", () => {
+		it("should strip maxItems from array schemas for Bedrock compatibility", () => {
+			const schema = {
+				type: "object",
+				properties: {
+					names: {
+						type: "array",
+						items: { type: "string" },
+						maxItems: 4,
+					},
+				},
+			}
+
+			const result = provider.testConvertToolSchemaForOpenAI(schema)
+
+			// maxItems should be stripped by normalizeToolSchema for Bedrock
+			// compatibility (Bedrock doesn't support maxItems in its JSON Schema
+			// 2020-12 subset)
+			expect(result.properties.names.type).toBe("array")
+			expect(result.properties.names.items).toEqual({ type: "string" })
+			expect(result.properties.names.maxItems).toBeUndefined()
+		})
+
+		it("should convert nullable types to anyOf (JSON Schema 2020-12)", () => {
 			const schema = {
 				type: "object",
 				properties: {
@@ -150,14 +172,27 @@ describe("BaseProvider", () => {
 
 			const result = provider.testConvertToolSchemaForOpenAI(schema)
 
-			expect(result.properties.name.type).toBe("string")
+			// After normalization, type arrays are converted to anyOf for
+			// JSON Schema 2020-12 compliance. The nullable types are no longer
+			// stripped — they're properly represented as anyOf alternatives.
+			expect(result.properties.name.anyOf).toEqual([{ type: "string" }, { type: "null" }])
+			// Verify the stale type array field is gone after normalization
+			expect(result.properties.name.type).toBeUndefined()
 		})
 
-		it("should return non-object schemas unchanged", () => {
-			const schema = { type: "string" }
+		it("should flatten type arrays on non-object schemas", () => {
+			// Use type: ["string"] (single-element type array) which normalization
+			// converts to anyOf format (JSON Schema 2020-12 compliance) - proving
+			// non-object schemas are processed through normalizeToolSchema
+			const schema = { type: ["string"] }
 			const result = provider.testConvertToolSchemaForOpenAI(schema)
 
-			expect(result).toEqual(schema)
+			// The type array is normalized to anyOf format, type field is dropped
+			expect(result.type).toBeUndefined()
+			expect(result.anyOf).toBeDefined()
+			expect(result.anyOf).toContainEqual({ type: "string" })
+			// Normalization does not add additionalProperties to non-object schemas
+			expect(result.additionalProperties).toBeUndefined()
 		})
 
 		it("should return null/undefined unchanged", () => {

src/api/providers/base-provider.ts

@@ -6,6 +6,7 @@ import type { ApiHandler, ApiHandlerCreateMessageMetadata } from "../index"
 import { ApiStream } from "../transform/stream"
 import { countTokens } from "../../utils/countTokens"
 import { isMcpTool } from "../../utils/mcp-name"
+import { normalizeToolSchema } from "../../utils/json-schema"
 import { getApiRequestTimeout } from "./utils/timeout-config"
 
 /**
@@ -56,6 +57,8 @@ export abstract class BaseProvider implements ApiHandler {
 
 	/**
 	 * Converts tool schemas to be compatible with OpenAI's strict mode by:
+	 * - Normalizing for JSON Schema 2020-12 compliance (strips unsupported
+	 *   keywords like maxItems that backends like Bedrock reject)
 	 * - Ensuring all properties are in the required array (strict mode requirement)
 	 * - Converting nullable types (["type", "null"]) to non-nullable ("type")
 	 * - Adding additionalProperties: false to all object schemas (required by OpenAI Responses API)
@@ -64,11 +67,30 @@ export abstract class BaseProvider implements ApiHandler {
 	 * This matches the behavior of ensureAllRequired in openai-native.ts
 	 */
 	protected convertToolSchemaForOpenAI(schema: any): any {
-		if (!schema || typeof schema !== "object" || schema.type !== "object") {
+		if (!schema || typeof schema !== "object") {
 			return schema
 		}
 
-		const result = { ...schema }
+		// Normalize for JSON Schema 2020-12 compliance first: converts
+		// deprecated type arrays to anyOf, strips unsupported format
+		// values, and adds additionalProperties: false. Required for
+		// backends like Bedrock that enforce strict 2020-12 compliance.
+		const normalized = normalizeToolSchema(schema as Record<string, unknown>)
+
+		if (!normalized || typeof normalized !== "object") {
+			return normalized
+		}
+
+		// Check if the schema represents an object type:
+		// - Direct type: "object" (standard case)
+		// - Has "properties" (handles nullable objects that were converted to
+		//   anyOf by normalization — type is no longer "object" but properties
+		//   are preserved at the top level so strict-mode processing still applies)
+		if (normalized.type !== "object" && !normalized.properties) {
+			return normalized
+		}
+
+		const result: Record<string, any> = { ...normalized }
 
 		// OpenAI Responses API requires additionalProperties: false on all object schemas
 		// Only add if not already set to false (to avoid unnecessary mutations)

src/utils/json-schema.ts

@@ -26,8 +26,10 @@ const OPENAI_SUPPORTED_FORMATS = new Set([
 /**
  * Array-specific JSON Schema properties that must be nested inside array type variants
  * when converting to anyOf format (JSON Schema draft 2020-12).
+ * Note: maxItems and minItems are excluded from this list because AWS Bedrock
+ * does not support them in its JSON Schema 2020-12 implementation.
  */
-const ARRAY_SPECIFIC_PROPERTIES = ["items", "minItems", "maxItems", "uniqueItems"] as const
+const ARRAY_SPECIFIC_PROPERTIES = ["items", "uniqueItems"] as const
 
 /**
  * Applies array-specific properties from source to target object.
@@ -165,6 +167,9 @@ const NormalizedToolSchemaInternal: z.ZodType<Record<string, unknown>, z.ZodType
 					minItems,
 					maxItems,
 					uniqueItems,
+					minLength,
+					maxLength,
+					pattern,
 					...rest
 				} = schema
 				const result: Record<string, unknown> = { ...rest }