fix(otel): fix double-serialization of span attributes

[simonvdk-mistral]

Problem

gen_ai.input.messages, gen_ai.output.messages, and gen_ai.tool.definitions span attributes were double-serialized. Each message/definition was individually json.dumps()-ed into a list[str], which the OTEL exporter then serialized again on export, producing escaped JSON:

"[\"{\\\"role\\\": \\\"user\"\\, ...

A minor related issue: gen_ai.tool.call.result was unconditionally json.dumps()-ed without checking if the value was already a string.

Fix

Per the OTEL GenAI semantic conventions, these attributes are typed any and should be recorded as a single JSON string when structured attributes are not supported on spans (which is the case for the Python OTEL SDK today).

• Formatting helpers (serialize_* -> format_*) now return dict instead of str
• Callers in otel.py collect into list[dict], then do a single json.dumps() per attribute
• gen_ai.tool.call.result now has an isinstance(str) guard matching tool.call.arguments
• Renamed serialization.py -> formatting.py to reflect that these functions format, not serialize

References

• OTEL GenAI input messages JSON schema
• OTEL GenAI span examples

[louis-sanna-dev]

🔭