feat(ai): add requestMetadata support to BedrockOptions for cost allocation tagging (#2511)

Add an optional requestMetadata field to BedrockOptions that forwards
key-value pairs to the Bedrock Converse API ConverseStreamCommand. Tags
appear in AWS Cost Explorer split cost allocation data, enabling callers
to attribute inference costs to specific applications or contexts.

Changes:
- Add requestMetadata?: Record<string, string> to BedrockOptions with
  JSDoc documenting AWS constraints (max 50 pairs, key 64 chars, value
  256 chars, no aws: prefix)
- Pass requestMetadata to commandInput via conditional spread to avoid
  sending undefined when omitted
- Export BedrockOptions from package root (consistent with other
  provider option types)
- Add E2E tests: metadata forwarded to SDK payload, and omitted when
  not provided

closes #2510

packages/ai/src/index.ts

@@ -4,6 +4,7 @@ export { Type } from "@sinclair/typebox";
 export * from "./api-registry.js";
 export * from "./env-api-keys.js";
 export * from "./models.js";
+export type { BedrockOptions } from "./providers/amazon-bedrock.js";
 export type { AnthropicOptions } from "./providers/anthropic.js";
 export type { AzureOpenAIResponsesOptions } from "./providers/azure-openai-responses.js";
 export type { GoogleOptions } from "./providers/google.js";

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

@@ -55,6 +55,11 @@ export interface BedrockOptions extends StreamOptions {
 	thinkingBudgets?: ThinkingBudgets;
 	/* Only supported by Claude 4.x models, see https://docs.aws.amazon.com/bedrock/latest/userguide/claude-messages-extended-thinking.html#claude-messages-extended-thinking-tool-use-interleaved */
 	interleavedThinking?: boolean;
+	/** Key-value pairs attached to the inference request for cost allocation tagging.
+	 * Keys: max 64 chars, no `aws:` prefix. Values: max 256 chars. Max 50 pairs.
+	 * Tags appear in AWS Cost Explorer split cost allocation data.
+	 * @see https://docs.aws.amazon.com/bedrock/latest/APIReference/API_runtime_ConverseStream.html */
+	requestMetadata?: Record<string, string>;
 }
 
 type Block = (TextContent | ThinkingContent | ToolCall) & { index?: number; partialJson?: string };
@@ -153,6 +158,7 @@ export const streamBedrock: StreamFunction<"bedrock-converse-stream", BedrockOpt
 				inferenceConfig: { maxTokens: options.maxTokens, temperature: options.temperature },
 				toolConfig: convertToolConfig(context.tools, options.toolChoice),
 				additionalModelRequestFields: buildAdditionalModelRequestFields(model, options),
+				...(options.requestMetadata !== undefined && { requestMetadata: options.requestMetadata }),
 			};
 			const nextCommandInput = await options?.onPayload?.(commandInput, model);
 			if (nextCommandInput !== undefined) {