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69e310f | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 | """Langfuse tracing for every model call and every graph step.
Tracing is strictly optional: with no Langfuse keys configured the tracer is a
no-op that costs nothing and never raises. This keeps "I debug agents by reading
traces, not by guessing" true in production without making local development or
CI depend on a third-party service.
"""
from __future__ import annotations
import logging
from collections.abc import Iterator
from contextlib import contextmanager
from types import TracebackType
from typing import Any, Protocol, Self
from app.core.budget import Usage
from app.core.settings import Settings, get_settings
logger = logging.getLogger(__name__)
ObservationType = str
class _Observation(Protocol):
"""The subset of a Langfuse observation this module relies on."""
def update(self, **kwargs: Any) -> Any: ...
def end(self, **kwargs: Any) -> Any: ...
class _NullSpan:
"""No-op observation used when tracing is disabled."""
def update(self, **kwargs: Any) -> None: # noqa: ARG002 - protocol shape
return None
def end(self, **kwargs: Any) -> None: # noqa: ARG002 - protocol shape
return None
def __enter__(self) -> Self:
return self
def __exit__(
self,
exc_type: type[BaseException] | None,
exc: BaseException | None,
tb: TracebackType | None,
) -> None:
return None
class Tracer:
"""Thin, failure-tolerant wrapper over the Langfuse client."""
def __init__(self, settings: Settings | None = None) -> None:
self._settings = settings or get_settings()
self._client: Any | None = None
if not self._settings.langfuse_enabled:
return
try:
from langfuse import Langfuse
self._client = Langfuse(
public_key=self._settings.langfuse_public_key,
secret_key=self._settings.langfuse_secret_key,
host=self._settings.langfuse_host,
environment=self._settings.environment,
)
except Exception:
logger.warning("Langfuse initialisation failed; continuing untraced", exc_info=True)
self._client = None
@property
def enabled(self) -> bool:
return self._client is not None
# ------------------------------------------------------------------ api ---
@contextmanager
def step(
self,
name: str,
*,
run_id: str,
as_type: ObservationType = "span",
input_data: Any = None,
metadata: dict[str, Any] | None = None,
) -> Iterator[_Observation]:
"""Trace one graph step. Yields an observation you can `.update(output=...)`."""
if self._client is None:
yield _NullSpan()
return
span: Any = None
try:
span = self._client.start_observation(
name=name,
as_type=as_type,
input=input_data,
metadata={"run_id": run_id, **(metadata or {})},
)
except Exception:
logger.debug("langfuse start_observation failed", exc_info=True)
yield _NullSpan()
return
try:
yield span
except Exception as exc:
self._safe(span.update, level="ERROR", status_message=str(exc)[:500])
self._safe(span.end)
raise
else:
self._safe(span.end)
def record_generation(
self,
name: str,
*,
run_id: str,
model: str,
input_data: Any,
output_data: Any,
usage: Usage,
cost_usd: float,
metadata: dict[str, Any] | None = None,
) -> None:
"""Record a completed model call with token spend and cost."""
if self._client is None:
return
try:
generation = self._client.start_observation(
name=name,
as_type="generation",
model=model,
input=input_data,
metadata={"run_id": run_id, **(metadata or {})},
)
except Exception:
logger.debug("langfuse generation failed", exc_info=True)
return
self._safe(
generation.update,
output=output_data,
usage_details={
"input": usage.input_tokens,
"output": usage.output_tokens,
"cache_read_input_tokens": usage.cache_read_tokens,
"cache_creation_input_tokens": usage.cache_write_tokens,
"total": usage.total_tokens,
},
cost_details={"total": cost_usd},
)
self._safe(generation.end)
def flush(self) -> None:
if self._client is None:
return
self._safe(self._client.flush)
def shutdown(self) -> None:
if self._client is None:
return
self._safe(self._client.shutdown)
self._client = None
# -------------------------------------------------------------- internal ---
@staticmethod
def _safe(fn: Any, **kwargs: Any) -> None:
try:
fn(**kwargs)
except Exception:
logger.debug("langfuse call failed", exc_info=True)
_tracer: Tracer | None = None
def get_tracer() -> Tracer:
"""Process-wide tracer singleton."""
global _tracer # noqa: PLW0603 - deliberate process-wide singleton
if _tracer is None:
_tracer = Tracer()
return _tracer
def reset_tracer() -> None:
"""Test hook."""
global _tracer # noqa: PLW0603 - deliberate process-wide singleton
if _tracer is not None:
_tracer.shutdown()
_tracer = None
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