Migrate from legacy ingestion API to OTLP endpoint

- Replace custom Exporter with OpenTelemetry OTLP exporter
- Update endpoint from /api/public/ingestion to /api/public/otel/v1/traces
- Migrate attribute namespace (langfuse.type → langfuse.observation.type, etc.)
- Remove obsolete IngestionClient and custom Exporter classes
- Update all tests to match new OTLP endpoint and attribute format
- Add opentelemetry-exporter-otlp gem dependency

This fixes the issue where nested spans weren't appearing in Langfuse UI.
The OTLP endpoint properly handles out-of-order spans using OpenTelemetry's
standard parent-child relationships via span_id and parent_span_id.

Author: NoahFisher

.claude/settings.local.json

@@ -9,7 +9,8 @@
       "Bash(mkdir:*)",
       "WebSearch",
       "Read(//Users/noah/dev/simplepractice/simplepractice/**)",
-      "WebFetch(domain:github.com)"
+      "WebFetch(domain:github.com)",
+      "WebFetch(domain:langfuse.com)"
     ],
     "deny": [],
     "ask": []

Gemfile.lock

@@ -7,6 +7,7 @@ PATH
       mustache (~> 1.1)
       opentelemetry-api (~> 1.2)
       opentelemetry-common (~> 0.21)
+      opentelemetry-exporter-otlp (~> 0.28)
       opentelemetry-sdk (~> 1.4)
 
 GEM
@@ -29,6 +30,14 @@ GEM
       net-http (>= 0.5.0)
     faraday-retry (2.3.2)
       faraday (~> 2.0)
+    google-protobuf (4.33.0-arm64-darwin)
+      bigdecimal
+      rake (>= 13)
+    google-protobuf (4.33.0-x86_64-linux-gnu)
+      bigdecimal
+      rake (>= 13)
+    googleapis-common-protos-types (1.22.0)
+      google-protobuf (~> 4.26)
     hashdiff (1.2.1)
     json (2.15.1)
     language_server-protocol (3.17.0.5)
@@ -40,6 +49,13 @@ GEM
     opentelemetry-api (1.7.0)
     opentelemetry-common (0.23.0)
       opentelemetry-api (~> 1.0)
+    opentelemetry-exporter-otlp (0.31.0)
+      google-protobuf (>= 3.18)
+      googleapis-common-protos-types (~> 1.3)
+      opentelemetry-api (~> 1.1)
+      opentelemetry-common (~> 0.20)
+      opentelemetry-sdk (~> 1.2)
+      opentelemetry-semantic_conventions
     opentelemetry-registry (0.4.0)
       opentelemetry-api (~> 1.1)
     opentelemetry-sdk (1.10.0)

langfuse.gemspec

@@ -37,6 +37,7 @@ Gem::Specification.new do |spec|
   # Runtime dependencies - OpenTelemetry (for tracing)
   spec.add_dependency "opentelemetry-api", "~> 1.2"
   spec.add_dependency "opentelemetry-common", "~> 0.21"
+  spec.add_dependency "opentelemetry-exporter-otlp", "~> 0.28"
   spec.add_dependency "opentelemetry-sdk", "~> 1.4"
 
   # Development dependencies are specified in Gemfile

lib/langfuse.rb

@@ -29,8 +29,6 @@ class UnauthorizedError < ApiError; end
 require_relative "langfuse/config"
 require_relative "langfuse/prompt_cache"
 require_relative "langfuse/api_client"
-require_relative "langfuse/ingestion_client"
-require_relative "langfuse/exporter"
 require_relative "langfuse/otel_setup"
 require_relative "langfuse/tracer"
 require_relative "langfuse/trace"