fix(otel): configurable baggage, pass-through + service spans, typed guardrails - #29263

Summary

Follow-up to #28909 (typed semconv-aligned OpenTelemetry V2 instrumentation). This branch carries that work plus fixes for four problems found in it. All changes stay gated behind LITELLM_OTEL_V2.

1. Baggage allowlists are configurable (not hard-coded)

baggage_promoted_keys / baggage_metadata_keys previously had no env or config wiring. They are now configurable two ways:

• Env vars (comma-separated): LITELLM_OTEL_BAGGAGE_PROMOTED_KEYS, LITELLM_OTEL_BAGGAGE_METADATA_KEYS. A NoDecode + field_validator(mode="before") lets a plain a,b,c string parse into a list (pydantic-settings would otherwise demand JSON).
• config.yaml: callback_settings.otel.baggage_promoted_keys (a YAML list). These reach the config because the OpenTelemetryV2 constructor now builds OpenTelemetryV2Config(**kwargs) from the settings passed through.

2. Pass-through LLM-call span no longer missing

Pass-through endpoints dispatch their logging from a detached asyncio.create_task whose copied OTel context may no longer carry the server span, so the LLM-call span was dropped / orphaned. Fix:

• The pass-through endpoint now threads the proxy server span as litellm_parent_otel_span in request metadata (matching what normal proxy routes already do).
• _emit_llm_call falls back to that explicitly-threaded parent span when the ambient context has no recordable span. The normal path (ambient server span present) is unchanged.

3. Service spans no longer always missing

litellm/_service_logger.py only dispatched to loggers that were instances of the legacy OpenTelemetry. The V2 OpenTelemetryV2 is a plain CustomLogger, so it never matched and Redis/Postgres service spans were always dropped. The dispatch now resolves both the legacy and V2 OTel loggers (via a lazily-imported, SDK-optional helper), whether registered as an instance or as the "otel" string.

4. Guardrail span data is typed and provider-agnostic

GuardrailSpanData.from_logging_entry was untyped (Mapping[str, object]) and read ad-hoc bare keys (name/status/mode) that match no single schema. It now:

• Takes the typed StandardLoggingGuardrailInformation and reads only its canonical, provider-agnostic keys.
• Normalizes guardrail_mode (a GuardrailEventHooks enum, a list of them, or a GuardrailMode) to a stable string — e.g. "pre_call", not "GuardrailEventHooks.pre_call", and joins multiple modes.
• Surfaces the additional provider-agnostic fields guardrail_id, policy_template, detection_method as span attributes.

Tests

• New tests/test_litellm/integrations/otel/test_otel_v2_config_fixes.py — baggage env/config wiring, pass-through threaded-parent fallback (and ambient-wins precedence), guardrail mode normalization + typed metadata mapping.
• Extended tests/test_litellm/test_service_logger.py — V2 logger is recognized by the service-span dispatch (instance, "otel" string, unrelated-callback no-op) and an end-to-end service span is emitted.
• Full tests/test_litellm/integrations/otel/ suite passes; ruff / mypy / black clean on the changed files.

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