fix(langfuse): fix latency display showing incorrect huge hours value #688
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## Problem
Langfuse UI was displaying incorrect latency values like "17751749h"
instead of the actual duration in milliseconds (e.g., "854ms").
## Root Cause
The callback handler was not preserving the original `startTime` when
updating spans/generations in `OnEnd`. This caused the `startTime` to be
reset to zero value ("0001-01-01T00:00:00Z"), which Langfuse backend
uses to calculate latency as `endTime - startTime`, resulting in a
massive time difference.
## Solution
1. Add `Duration` field (milliseconds) to `SpanEventBody` and
`GenerationEventBody` in event data model
2. Store `startTime` in callback state during `OnStart`
3. Preserve original `startTime` and calculate `duration` in `OnEnd`
## Changes
- `libs/acl/langfuse/event.go`: Add `Duration *int64` field
- `callbacks/langfuse/langfuse.go`: Track startTime and compute duration
- `callbacks/langfuse/go.mod`: Add local replace for development
Co-Authored-By: Claude Opus 4.6 <[email protected]>
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Problem
Langfuse UI was displaying incorrect latency values like "17751749h 37m 57s"
instead of the actual duration in milliseconds (e.g., "854ms").
Root Cause
The callback handler was not preserving the original
startTimewhenupdating spans/generations in
OnEnd. This caused thestartTimeto bereset to zero value (
"0001-01-01T00:00:00Z"), which Langfuse backenduses to calculate latency as
endTime - startTime, resulting in amassive time difference.
Solution
Durationfield (milliseconds) toSpanEventBodyandGenerationEventBodyin event data modelstartTimein callback state duringOnStartstartTimeand calculatedurationinOnEndChanges
libs/acl/langfuse/event.go: AddDuration *int64field (milliseconds)callbacks/langfuse/langfuse.go: Track startTime and compute durationTesting
Before fix:
Latency: 17751749h 37m 57s❌After fix:
Latency: 854ms✅Co-Authored-By: Claude Opus 4.6 [email protected]