▚▚ fix(sdk/python): send the SigV4-signed payload bytes to Bedrock

[breken-ai]

Calling the Python SDK with a bedrock/... model fails on every request: AWS returns a SigV4 signature mismatch, because the payload hash the SDK signs is computed over different bytes than the ones httpx actually sends.

Root cause

call_provider in sdk/python/src/safety_agent/providers/__init__.py signs the Bedrock request over json.dumps(request_body) (default ", " / ": " separators) and puts that hash in x-amz-content-sha256 and the canonical request. It then posts the request with json=request_body. httpx >= 0.28 serialises json= with compact (",", ":") separators, so the body on the wire no longer matches the signed payload. pyproject.toml only requires httpx>=0.27.0 and no lockfile is committed, so a fresh uv sync installs 0.28.x and every Bedrock call is rejected.

Fix

• sdk/python/src/safety_agent/providers/__init__.py: build a request_kwargs dict that is {"json": request_body} for every provider and {"content": payload.encode("utf-8")} for bedrock, where payload is the exact string that was signed. The three client.post(...) sites use **request_kwargs instead of json=request_body. Behaviour for all non-bedrock providers is unchanged.

Tests

• sdk/python/tests/test_bedrock_provider.py (new): mocks httpx.AsyncClient, calls call_provider("bedrock/..."), rebuilds the request with httpx.Request(...) from the kwargs that were passed to post, and asserts sha256(request.content) equals the x-amz-content-sha256 header. Fails on main (hash mismatch), passes with the fix.
• uv run pytest in sdk/python: 153 passed.

Not changed

• The signing itself (BedrockProvider.get_signed_headers) is untouched; it was correct for the string it was given.
• Not verified against a live Bedrock endpoint (no AWS credentials available; the Python CI job does not receive AWS_BEDROCK_API_KEY either, which is why this never surfaced in CI).

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▚▚ Shipped by breken — self-healing software. This one's on us. breken.ai

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Note

Low Risk
Targeted HTTP transport change for Bedrock only; non-Bedrock providers still use json= and signing logic is unchanged.

Overview
Fixes Bedrock SigV4 failures caused by a mismatch between the payload bytes signed for AWS and the body httpx actually sends when using json=request_body (compact JSON in httpx 0.28+ vs the string from json.dumps used for signing).

call_provider now builds shared request_kwargs: default {"json": request_body} for other providers, and for bedrock {"content": payload.encode("utf-8")} where payload is the exact string passed into signing. All three client.post paths use **request_kwargs instead of hard-coded json=.

Adds test_bedrock_provider.py with a mocked httpx call that asserts x-amz-content-sha256 matches sha256 of the wire body rebuilt from the post kwargs.

^{Reviewed by Cursor Bugbot for commit 27776c4. Configure here.}

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