pickBodyText serialized any non-empty object into the error body. SDK error
fields can hold class instances instead of parsed bodies - AWS SDK v3's
$response.body is an HTTP stream/response wrapper - and stringifying one
produced garbage like {"_events":...} as the body, which then replaced
error.message in the composed display string. error.message is where the SDK
puts the real deserialized exception text ("Input is too long...", schema
validation details), so the one useful string was discarded for noise.
The existing pipe-based stream sniffing only covers node-style streams; web
ReadableStreams (pipeTo/pipeThrough, no pipe) and non-stream wrapper classes
slipped through. Require Object.prototype/null prototype before serializing
a candidate body - parsed JSON bodies are plain objects by construction, so
real gateway bodies still surface.
Add a shared normalizeProviderError helper in packages/ai/src/utils/error-body.ts
and route the 8 body-blind / status-only providers through it (amazon-bedrock,
azure-openai-responses, google, google-vertex, images/openrouter,
openai-codex-responses, openai-completions, openai-responses). Non-schema 4xx/5xx
responses from proxies / gateways now show the real reason carried in the response
body alongside the HTTP status, instead of "403 status code (no body)" or
"Unknown: UnknownError".
The helper probes status (statusCode, status, $metadata.httpStatusCode,
$response.statusCode) and body (body, parsed error object, $response.body) across
the Mistral, OpenAI, Google, and Bedrock SDK shapes, truncates the body at a 4000
char cap, and preserves error.message when the SDK already folded the body in
(Anthropic / Google happy path). mistral.ts and anthropic.ts are left untouched.
Provider prefixes and the OpenRouter metadata.raw append are preserved.
closes#5763
