Telemetry - Fused

Harnest provides the same logging and tracing API for ADK and LangGraph.

Signal	Use it for	Default destination
Structured logs	Searchable runtime events	JSON on stderr
Traces	Timing and causality	Disabled until configured
Audit events	Durable mutation outcomes	Configured OTEL destination
Playground traces	Local debugging	Process memory

Add logs and spans

from harnest.logging import get_logger
from harnest.tracing import span, traced

logger = get_logger("catalog").bind(component="search")


@traced("catalog.lookup", attributes={"catalog.kind": "products"})
def lookup(query: str):
    with span("catalog.rank", candidate_count=12):
        logger.info("catalog.lookup.completed", result_count=3)
        return ["one", "two", "three"]

Logs inside a span carry its trace and span IDs.

Configure OTLP

export OTEL_SERVICE_NAME=support-agent
export OTEL_EXPORTER_OTLP_ENDPOINT=http://127.0.0.1:4318
export OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf
export HARNEST_LOG_LEVEL=INFO
harnest serve support-agent

Property	Purpose
`OTEL_SERVICE_NAME`	Service identity
`OTEL_EXPORTER_OTLP_ENDPOINT`	Collector endpoint
`OTEL_EXPORTER_OTLP_PROTOCOL`	Export protocol
`HARNEST_LOG_LEVEL`	Minimum log level
`HARNEST_LOG_CONSOLE=false`	Disable JSON stderr logs

Standard per-signal endpoints, headers, timeouts, compression, resources, and sampling variables also work. Keep exporter credentials in deployment secrets. Use a Collector for translation or fan-out.

Privacy boundary

Recorded by default	Not recorded by default
Operation names and outcomes	Prompts and responses
Timing fields with a bounded set of values	Credentials and headers
Correlated failures	Raw session IDs and payloads

The playground trace inspector is bounded, process-local debug state—not an audit store. Runtime mutations emit audit signals after commit. CLI and compiler file changes are outside this runtime audit boundary.