Create Langfuse::Types module with observation types and attribute classes

[kxzk]

Overview

Define observation type constants and attributes as the foundation for Langfuse domain models.

Context

• JS SDK defines observation types in packages/tracing/src/types.ts (lines 12-22)
• Attributes are typed as LangfuseSpanAttributes, LangfuseGenerationAttributes, etc.
• Ruby equivalent should use classes/modules for type safety

Technical Implementation

Create lib/langfuse/types.rb with:

Observation Type Constants

module Langfuse
  module Types
    OBSERVATION_TYPES = %w[
      span generation event embedding
      agent tool chain retriever
      evaluator guardrail
    ].freeze

    LEVELS = %w[DEBUG DEFAULT WARNING ERROR].freeze
  end
end

Attribute Classes

Base SpanAttributes:

• input, output, metadata, level
• status_message, version, environment
• #initialize(**kwargs) for keyword arg initialization
• #to_h for hash representation

GenerationAttributes (extends SpanAttributes):

• Additional: completion_start_time, model, model_parameters
• usage_details, cost_details, prompt
• Prompt should be hash: { name:, version:, is_fallback: }

EmbeddingAttributes (extends GenerationAttributes)

TraceAttributes:

• name, user_id, session_id, version, release
• input, output, metadata, tags, public, environment
• Same initialization pattern

Aliases for Span-like Types

EventAttributes = SpanAttributes
AgentAttributes = SpanAttributes
ToolAttributes = SpanAttributes
ChainAttributes = SpanAttributes
RetrieverAttributes = SpanAttributes
EvaluatorAttributes = SpanAttributes
GuardrailAttributes = SpanAttributes

Acceptance Criteria

• Langfuse::Types::OBSERVATION_TYPES contains all 10 types
• Langfuse::Types::SpanAttributes can be instantiated with keyword args
• Langfuse::Types::GenerationAttributes extends SpanAttributes
• #to_h returns hash representation of attributes
• All attribute classes documented with YARD
• Unit tests for each attribute class

Files to Create

• lib/langfuse/types.rb - Type definitions
• spec/langfuse/types_spec.rb - Tests

Dependencies

None