Skip to content

Trace reasoning messages in Langfuse #4

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
bezbac merged 1 commit into from
Jul 2, 2026
Merged

Trace reasoning messages in Langfuse #4

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
14 changes: 7 additions & 7 deletions src/index.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,7 @@ type SessionNextEvent =
properties: {
sessionID: string;
timestamp: number;
assistantMessageID: string;
reasoningID: string;
text: string;
};
Expand Down Expand Up @@ -165,6 +166,7 @@ const eventHook = (event: OpencodeEvent, shutdown?: () => Promise<void>) =>

if (event.type === "message.part.updated") {
langfuse.rememberAssistantPart(event.properties.part);
langfuse.traceReasoningPart(event.properties.part);
}

if (event.type === "session.next.step.started") {
Expand Down Expand Up @@ -200,15 +202,13 @@ const eventHook = (event: OpencodeEvent, shutdown?: () => Promise<void>) =>
}

if (event.type === "session.next.reasoning.ended") {
langfuse.traceEvent({
id: event.id,
langfuse.traceReasoning({
reasoningID: event.properties.reasoningID,
sessionID: event.properties.sessionID,
name: "opencode.generation.reasoning",
timestamp: event.properties.timestamp,
output: { text: event.properties.text },
metadata: {
reasoningID: event.properties.reasoningID,
},
text: event.properties.text,
messageID: event.properties.assistantMessageID,
source: "session.next.reasoning.ended",
});
}

Expand Down
178 changes: 177 additions & 1 deletion src/langfuse.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,9 @@ export class LangfuseClient {
this.traceState.assistantParts.clear();
this.traceState.abortedSessions.clear();
this.traceState.tracedEventIds.clear();
this.traceState.tracedReasoningIds.clear();
this.traceState.pendingReasoningPartsByMessageId.clear();
this.traceState.generationSpansByMessageId.clear();
this.traceState.generationParentSpans.clear();
this.traceState.turnObservationsByMessageId.clear();
this.traceState.latestTurnObservationsBySession.clear();
Expand Down Expand Up @@ -103,14 +106,15 @@ export class LangfuseClient {
input?: unknown;
output?: unknown;
metadata?: unknown;
parentSpan?: ApiSpan;
}) {
if (this.traceState.tracedEventIds.has(input.id)) {
return;
}

this.traceState.tracedEventIds.add(input.id);

this.withObservationParent(input.sessionID, () => {
const startEvent = () => {
const span = this.traceState.tracer.startSpan(input.name, {
attributes: {
"langfuse.observation.type": "event",
Expand All @@ -127,6 +131,98 @@ export class LangfuseClient {
});

span.end(new Date(input.timestamp));
};

if (input.parentSpan) {
context.with(
trace.setSpan(context.active(), input.parentSpan),
startEvent,
);
return;
}

this.withObservationParent(input.sessionID, startEvent);
}

traceReasoning(input: {
reasoningID: string;
sessionID: string;
timestamp: number;
text: string;
messageID?: string;
source: string;
parentSpan?: ApiSpan;
}) {
if (!input.text.trim()) {
return;
}

const reasoningTraceKey = `${input.sessionID}:${input.reasoningID}`;

if (this.traceState.tracedReasoningIds.has(reasoningTraceKey)) {
return;
}

this.traceState.tracedReasoningIds.add(reasoningTraceKey);

const parentSpan =
input.parentSpan ??
(input.messageID
? this.traceState.generationSpansByMessageId.get(input.messageID)
: undefined);

const generationParentSpan =
parentSpan ??
this.traceState.activeGenerationSteps.get(input.sessionID)?.span ??
this.traceState.generationParentSpans.get(input.sessionID);

this.traceEvent({
id: `reasoning:${reasoningTraceKey}`,
sessionID: input.sessionID,
name: "opencode.generation.reasoning",
timestamp: input.timestamp,
output: { text: input.text },
metadata: {
reasoningID: input.reasoningID,
messageID: input.messageID,
source: input.source,
},
parentSpan: generationParentSpan,
});
}

traceReasoningPart(part: MessagePart) {
const completed = getCompletedReasoningTimestamp(part);

if (!isCompletedReasoningPart(part) || completed === undefined) {
return;
}

const generationSpan =
this.traceState.generationSpansByMessageId.get(part.messageID) ??
this.traceState.activeGenerationSteps.get(part.sessionID)?.span ??
this.traceState.generationParentSpans.get(part.sessionID);

if (!generationSpan) {
const pending =
this.traceState.pendingReasoningPartsByMessageId.get(part.messageID) ??
new Map<string, CompletedReasoningPart>();
pending.set(part.id, part);
this.traceState.pendingReasoningPartsByMessageId.set(
part.messageID,
pending,
);
return;
}

this.traceReasoning({
reasoningID: part.id,
sessionID: part.sessionID,
timestamp: completed,
text: part.text,
messageID: part.messageID,
source: "message.part.updated",
parentSpan: generationSpan,
});
}

Expand Down Expand Up @@ -415,6 +511,12 @@ export class LangfuseClient {
}),
);

this.traceState.generationSpansByMessageId.set(
input.messageID,
step.span,
);
this.flushPendingReasoning(input.messageID, step.span);

step.span.end(new Date(input.completed));
this.traceState.activeGenerationSteps.delete(input.sessionID);

Expand Down Expand Up @@ -458,10 +560,37 @@ export class LangfuseClient {
});

this.traceState.generationParentSpans.set(input.sessionID, span);
this.traceState.generationSpansByMessageId.set(input.messageID, span);
this.flushPendingReasoning(input.messageID, span);
span.end(new Date(input.completed));
});
}

private flushPendingReasoning(messageID: string, parentSpan: ApiSpan) {
const pending =
this.traceState.pendingReasoningPartsByMessageId.get(messageID) ??
new Map<string, CompletedReasoningPart>();
this.traceState.pendingReasoningPartsByMessageId.delete(messageID);

for (const part of pending.values()) {
const completed = getCompletedReasoningTimestamp(part);

if (completed === undefined) {
continue;
}

this.traceReasoning({
reasoningID: part.id,
sessionID: part.sessionID,
timestamp: completed,
text: part.text,
messageID: part.messageID,
source: "message.part.updated",
parentSpan,
});
}
}

traceFailedGenerationStep(input: {
id: string;
sessionID: string;
Expand Down Expand Up @@ -736,6 +865,12 @@ export type LangfuseTraceState = {
tracedMessageIds: Set<string>;
tracedGenerationIds: Set<string>;
tracedEventIds: Set<string>;
tracedReasoningIds: Set<string>;
pendingReasoningPartsByMessageId: Map<
string,
Map<string, CompletedReasoningPart>
>;
generationSpansByMessageId: Map<string, ApiSpan>;
assistantParts: Map<string, Map<string, MessagePart>>;
turnObservationsByMessageId: Map<string, TurnObservation>;
latestTurnObservationsBySession: Map<string, TurnObservation>;
Expand All @@ -749,6 +884,41 @@ export type MessagePart = Extract<
{ type: "message.part.updated" }
>["properties"]["part"];

type CompletedReasoningPart = MessagePart & {
id: string;
sessionID: string;
text: string;
messageID: string;
time: { completed?: number; end?: number };
};

function isCompletedReasoningPart(
part: MessagePart,
): part is CompletedReasoningPart {
return (
part.type === "reasoning" &&
typeof part.id === "string" &&
typeof part.sessionID === "string" &&
typeof part.messageID === "string" &&
typeof part.text === "string" &&
typeof getCompletedReasoningTimestamp(part) === "number"
);
}

function getCompletedReasoningTimestamp(part: MessagePart) {
const time = (part as { time?: { completed?: unknown; end?: unknown } }).time;

if (typeof time?.completed === "number") {
return time.completed;
}

if (typeof time?.end === "number") {
return time.end;
}

return undefined;
}

export type FormattedMessagePart =
| { type: string; text: string }
| { type: string; filename?: string; url?: string }
Expand Down Expand Up @@ -851,6 +1021,12 @@ export const createLangfuseClient = (input: {
tracedMessageIds: new Set<string>(),
tracedGenerationIds: new Set<string>(),
tracedEventIds: new Set<string>(),
tracedReasoningIds: new Set<string>(),
pendingReasoningPartsByMessageId: new Map<
string,
Map<string, CompletedReasoningPart>
>(),
generationSpansByMessageId: new Map<string, ApiSpan>(),
assistantParts: new Map<string, Map<string, MessagePart>>(),
turnObservationsByMessageId: new Map<string, TurnObservation>(),
latestTurnObservationsBySession: new Map<string, TurnObservation>(),
Expand Down