Preserve nested trace metadata values

Author: marcusschiesser

packages/core/src/otel.ts

@@ -349,7 +349,8 @@ function langfuseAttributes(attributes: Record<string, unknown>): {
 	const traceMetadata: Record<string, unknown> = {};
 	for (const [key, value] of Object.entries(attributes)) {
 		if (key.startsWith("langfuse.trace.metadata.")) {
-			traceMetadata[key.slice("langfuse.trace.metadata.".length)] = value;
+			traceMetadata[key.slice("langfuse.trace.metadata.".length)] =
+				parseJsonMetadataValue(value);
 		}
 	}
 
@@ -367,3 +368,7 @@ function langfuseAttributes(attributes: Record<string, unknown>): {
 		tracePublic: booleanValue(attributes["langfuse.trace.public"]),
 	};
 }
+
+function parseJsonMetadataValue(value: unknown): unknown {
+	return typeof value === "string" ? parseJsonString(value) : value;
+}

packages/perf/src/load.ts

@@ -129,7 +129,9 @@ async function generateChildObservation(
 		return;
 	}
 
-	const updateSpanLikeObservation = async (span: LangfuseSpan | LangfuseTool) => {
+	const updateSpanLikeObservation = async (
+		span: LangfuseSpan | LangfuseTool,
+	) => {
 		span.update({
 			input: {
 				step: childIndex,

tests/cli.test.ts

@@ -142,6 +142,44 @@ test("CLI default trace ids are OTEL trace ids", () => {
 	assert.match(createOtelTraceId(), /^[0-9a-f]{32}$/);
 });
 
+test("CLI trace creation preserves nested metadata values", async () => {
+	const dbPath = join(
+		mkdtempSync(join(tmpdir(), "agentpond-cli-")),
+		"cache.duckdb",
+	);
+	const resourceSpans = manualTraceResourceSpans(
+		{
+			flags: {
+				metadata: '{"details":{"tier":"pro"},"tags":["a","b"],"plain":"ok"}',
+			},
+			positionals: [],
+		},
+		"0123456789abcdef0123456789abcdef",
+		"2026-06-14T11:03:19.419Z",
+	);
+	const store = new MemoryObjectStore();
+	await store.putJson(
+		"otel/default-project/2026/06/14/11/03/batch-1.json",
+		resourceSpans,
+	);
+	const db = new AgentPondDuckDb(dbPath);
+	await db.syncFromStore({
+		store,
+		projectId: "default-project",
+		prefix: "",
+	});
+	const traces = await db.query<{ metadata_json: string }>(
+		"SELECT metadata_json FROM traces WHERE id = '0123456789abcdef0123456789abcdef'",
+	);
+	await db.close();
+
+	assert.deepEqual(JSON.parse(traces[0].metadata_json), {
+		details: { tier: "pro" },
+		tags: ["a", "b"],
+		plain: "ok",
+	});
+});
+
 test("CLI-created scores are immediately visible to score list queries", async () => {
 	const store = new MemoryObjectStore();
 	const dbPath = join(