Feature request: allow customizing serializer on BedrockAgentResolver (parity with BedrockAgentFunctionResolver)

[kimnamu]

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Use case

A Bedrock Agent action group that returns non-ASCII text (e.g. Korean 잔액은 1,000원입니다 or emoji) is \uXXXX-escaped in responseBody.body, because BedrockResponseBuilder.build() (event_handler/bedrock_agent.py:42) serializes via the default json.dumps(..., ensure_ascii=True) serializer (api_gateway.py:1625).

Unlike ApiGatewayResolver and the sibling BedrockAgentFunctionResolver — both of which expose a serializer= argument (as noted by the maintainer in #7776) — BedrockAgentResolver.__init__ hardcodes serializer=None (bedrock_agent.py:102-111) with no way to override it. So there's no supported way to emit readable non-ASCII from a Bedrock Agent resolver.

Solution/User Experience

Expose the parent's existing serializer parameter on BedrockAgentResolver (no new abstraction — the same serializer param #6394 endorsed and the sibling function resolver already accepts). Users could then pass partial(json.dumps, ensure_ascii=False).

Alternative solutions

Defaulting the builder to ensure_ascii=False would be a behavior change; exposing the existing param is additive and lower-risk.

I'd be happy to open a small PR with a regression test.

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This issue was prepared with the help of an AI agent (Claude Code) and reviewed by a human.

[boring-cyborg]

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