Bedrock: audit ModelSpec.stream_response_path defaults per model family

[safayavatsal]

Context

Discovered while fixing #146 (Cohere) and #147 (Llama-3) on the Python SDK side. The SDK's event-stream parser now correctly decodes AWS Bedrock framing and extracts text via the configured stream_response_path JSONPath. But for streaming to actually yield text, the route's ModelSpec.stream_response_path must match the chunk schema emitted by that model.

Each Bedrock model family emits a different chunk shape, so a single default (currently delta.text) silently breaks the rest.

Known per-model chunk schemas

Model family	Correct stream_response_path
Anthropic Claude	delta.text
Meta Llama (3.x, 2)	generation
Cohere Command	text
Mistral (Bedrock)	outputs[0].text
AI21 Jamba	choices[0].delta.content
Amazon Titan Text	outputTokens[0].text (verify)

Ask

1. Audit existing routes/ModelSpecs for Bedrock-hosted models and confirm each carries the correct stream_response_path.
2. Set sensible per-family defaults in whatever creates ModelSpecs so new routes get the right path automatically.
3. Add a startup/validation check that flags routes pointing at a known Bedrock model family with an obviously wrong stream_response_path.

Why this is a separate ticket

The SDK change (event-stream parser rewrite, PR linked to #146/#147) is necessary but not sufficient. Even with a correct parser, a misconfigured stream_response_path produces an empty stream — now with a structured WARNING log naming the path that missed and the payload keys observed, so this audit is actionable.