Python bridge should disallow NaN/Infinity in JSON responses

[bbopen]

Summary

json.dumps in python_bridge.py allows NaN/Infinity by default, producing invalid JSON tokens (NaN, Infinity). Node’s JSON.parse rejects these and triggers protocol errors, killing the bridge.

Failure mode

• Python function returns float('nan') or float('inf') (or includes these values in a list/dict).
• json.dumps serializes them to NaN/Infinity.
• Node side fails to parse and treats it as a protocol error.

Evidence

• runtime/python_bridge.py encode_response() uses json.dumps(out) without allow_nan=False.

Proposed fix

• Use json.dumps(..., allow_nan=False) and surface a clear error when NaN/Infinity is encountered.
• Optionally sanitize to strings if a safe mode is configured.

Acceptance criteria

• NaN/Infinity in responses produce a clear, explicit error payload instead of invalid JSON.
• Node side does not receive malformed JSON for these values.
• Add tests with functions returning NaN/Infinity.