Use Langfuse client trace upsert API (#1041)

Replace direct trace.update calls with client trace upserts so OpenAI provider is compatible with langfuse-ruby 0.1.6 behavior. Add richer warning logs that include full exception details for trace creation, trace upserts, and generation logging failures. Add tests for client-based trace upserts and detailed error logging.

app/models/provider/openai.rb

@@ -82,7 +82,7 @@ class Provider::Openai < Provider
         json_mode: json_mode
       ).auto_categorize
 
-      trace&.update(output: result.map(&:to_h))
+      upsert_langfuse_trace(trace: trace, output: result.map(&:to_h))
 
       result
     end
@@ -110,7 +110,7 @@ class Provider::Openai < Provider
         json_mode: json_mode
       ).auto_detect_merchants
 
-      trace&.update(output: result.map(&:to_h))
+      upsert_langfuse_trace(trace: trace, output: result.map(&:to_h))
 
       result
     end
@@ -147,7 +147,7 @@ class Provider::Openai < Provider
         family: family
       ).process
 
-      trace&.update(output: result.to_h)
+      upsert_langfuse_trace(trace: trace, output: result.to_h)
 
       result
     end
@@ -168,7 +168,7 @@ class Provider::Openai < Provider
         model: effective_model
       ).extract
 
-      trace&.update(output: { transaction_count: result[:transactions].size })
+      upsert_langfuse_trace(trace: trace, output: { transaction_count: result[:transactions].size })
 
       result
     end
@@ -480,7 +480,7 @@ class Provider::Openai < Provider
         environment: Rails.env
       )
     rescue => e
-      Rails.logger.warn("Langfuse trace creation failed: #{e.message}")
+      Rails.logger.warn("Langfuse trace creation failed: #{e.message}\n#{e.full_message}")
       nil
     end
 
@@ -505,16 +505,32 @@ class Provider::Openai < Provider
           output: { error: error.message, details: error.respond_to?(:details) ? error.details : nil },
           level: "ERROR"
         )
-        trace&.update(
+        upsert_langfuse_trace(
+          trace: trace,
           output: { error: error.message },
           level: "ERROR"
         )
       else
         generation&.end(output: output, usage: usage)
-        trace&.update(output: output)
+        upsert_langfuse_trace(trace: trace, output: output)
       end
     rescue => e
-      Rails.logger.warn("Langfuse logging failed: #{e.message}")
+      Rails.logger.warn("Langfuse logging failed: #{e.message}\n#{e.full_message}")
+    end
+
+    def upsert_langfuse_trace(trace:, output:, level: nil)
+      return unless langfuse_client && trace&.id
+
+      payload = {
+        id: trace.id,
+        output: output
+      }
+      payload[:level] = level if level.present?
+
+      langfuse_client.trace(**payload)
+    rescue => e
+      Rails.logger.warn("Langfuse trace upsert failed for trace_id=#{trace&.id}: #{e.message}\n#{e.full_message}")
+      nil
     end
 
     def record_llm_usage(family:, model:, operation:, usage: nil, error: nil)

test/models/provider/openai_test.rb

@@ -286,4 +286,48 @@ class Provider::OpenaiTest < ActiveSupport::TestCase
 
     assert_equal "configured model: custom-model", custom_provider.supported_models_description
   end
+
+  test "upsert_langfuse_trace uses client trace upsert" do
+    trace = Struct.new(:id).new("trace_123")
+    fake_client = mock
+
+    fake_client.expects(:trace).with(id: "trace_123", output: { ok: true }, level: "ERROR")
+    @subject.stubs(:langfuse_client).returns(fake_client)
+
+    @subject.send(:upsert_langfuse_trace, trace: trace, output: { ok: true }, level: "ERROR")
+  end
+
+  test "log_langfuse_generation upserts trace through client" do
+    trace = Struct.new(:id).new("trace_456")
+    generation = mock
+    fake_client = mock
+
+    @subject.stubs(:langfuse_client).returns(fake_client)
+    @subject.stubs(:create_langfuse_trace).returns(trace)
+
+    fake_client.expects(:trace).with(id: "trace_456", output: "hello")
+    trace.expects(:generation).returns(generation)
+    generation.expects(:end).with(output: "hello", usage: { "total_tokens" => 10 })
+
+    @subject.send(
+      :log_langfuse_generation,
+      name: "chat",
+      model: "gpt-4.1",
+      input: { prompt: "Hi" },
+      output: "hello",
+      usage: { "total_tokens" => 10 }
+    )
+  end
+
+  test "create_langfuse_trace logs full error details" do
+    fake_client = mock
+    error = StandardError.new("boom")
+
+    @subject.stubs(:langfuse_client).returns(fake_client)
+    fake_client.expects(:trace).raises(error)
+
+    Rails.logger.expects(:warn).with(regexp_matches(/Langfuse trace creation failed: boom.*test\/models\/provider\/openai_test\.rb/m))
+
+    @subject.send(:create_langfuse_trace, name: "openai.test", input: { foo: "bar" })
+  end
 end