Bedrock validation errors serialize Http2Stream instead of the AWS exception message

[ashwin-pc]

Summary

When Bedrock returns a parsed ValidationException, pi-web only displays an opaque payload containing Node Http2Stream internals (_readableState, _writableState, allowHalfOpen, etc.) instead of the useful AWS SDK exception message.

This made a Fable account/region configuration error look like an unexplained model/session 400.

Reproduction

1. Use an Amazon Bedrock model in an account/region where the request is rejected at validation time. In this case Claude Fable 5 returned a data-retention configuration error.
2. Send any prompt through pi-web.
3. Observe the assistant error:

Validation error: 400: {"_events":...,"_readableState":...,"_writableState":...,"allowHalfOpen":true,...}

Actual underlying SDK exception

Instrumenting the Bedrock adapter's catch block showed that the AWS SDK had already parsed the response correctly:

ValidationException: The model returned the following errors:
data retention mode 'default' is not available for this model

The exception had:

name: ValidationException
$metadata.httpStatusCode: 400
message: The model returned the following errors: ...
$response.body: Http2Stream

Root cause

formatBedrockError() calls normalizeProviderError(error). The normalization/formatting path prefers or serializes $response.body when status/body are present, even though that body is an already-consumed Node HTTP/2 stream and error.message contains the parsed service error.

Relevant installed adapter:

@earendil-works/pi-ai/dist/api/bedrock-converse-stream.js

Expected behavior

Prefer the parsed AWS service exception message:

Validation error: The model returned the following errors: data retention mode 'default' is not available for this model

Only fall back to reading/formatting a raw response body when there is no meaningful parsed exception message. Never JSON-stringify a Node stream as the user-facing response body.

Impact

• Hides the actionable Bedrock remediation.
• Makes account/region configuration failures look like corrupt sessions or invalid model IDs.
• Complicates diagnosis of 400/403 provider failures.

Environment

• pi-web current main
• Amazon Bedrock Converse Stream provider
• Reproduced with a fresh session, zero token usage, and Claude Fable 5