fix(amazon-bedrock): handled stringify exceptions

Guard diagnostic JSON serialization so circular objects and BigInt values cannot escape the provider catch block. Expanded the regression coverage to undefined, BigInt, and circular thrown values.

Fixes #5539

packages/ai/CHANGELOG.md

@@ -4,7 +4,7 @@
 
 ### Fixed
 
-- Fixed Amazon Bedrock stream error handler crashing with `TypeError: undefined is not an object (evaluating 'baseMessage.includes')` when a non-`Error` value is thrown and `JSON.stringify` returns `undefined` ([#5539](https://github.com/can1357/oh-my-pi/issues/5539)).
+- Fixed Amazon Bedrock stream error handling for non-`Error` values that `JSON.stringify` cannot serialize ([#5539](https://github.com/can1357/oh-my-pi/issues/5539)).
 
 ## [16.5.2] - 2026-07-14
 

packages/ai/src/providers/amazon-bedrock.ts

@@ -510,7 +510,12 @@ export const streamBedrock: StreamFunction<"bedrock-converse-stream"> = (
 			for (const block of output.content) {
 				if (block.type === "toolCall") clearStreamingPartialJson(block);
 			}
-			const baseMessage = error instanceof Error ? error.message : (JSON.stringify(error) ?? String(error));
+			let baseMessage: string;
+			try {
+				baseMessage = error instanceof Error ? error.message : (JSON.stringify(error) ?? String(error));
+			} catch {
+				baseMessage = String(error);
+			}
 			// Enrich error with thinking block diagnostics for signature-related failures
 			let diagnostics = "";
 			if (baseMessage.includes("signature") || baseMessage.includes("thinking")) {

packages/ai/test/bedrock-inference-profile.test.ts

@@ -150,17 +150,19 @@ describe("Bedrock cross-region inference-profile geo routing", () => {
 });
 
 describe("Bedrock error handling", () => {
-	// Regression (#5539): a non-`Error` thrown inside the stream body where
-	// `JSON.stringify` returns `undefined` (e.g. `undefined`, a function, a
-	// circular object) must not crash the catch block via `baseMessage.includes(...)`.
-	// The stream must close cleanly with an error result instead of an unhandled
-	// `TypeError: undefined is not an object (evaluating 'baseMessage.includes')`.
-	test("surfaces a stream error when a non-Error value is thrown", async () => {
+	const circular: Record<string, unknown> = {};
+	circular.self = circular;
+
+	test.each([
+		["undefined", undefined],
+		["BigInt", 1n],
+		["circular object", circular],
+	])("surfaces a stream error when %s is thrown", async (_name, thrown) => {
 		const result = await streamBedrock(profileModel, userContext(), {
 			bearerToken: "test-token",
 			maxTokens: 16,
 			onPayload: () => {
-				throw undefined;
+				throw thrown;
 			},
 		}).result();