Add OpenTelemetry Instrumenter with PII Filtering and Argument Tracking

[johngallagher]

Summary

• Introduces a new Observable::Instrumenter class for automated OpenTelemetry instrumentation of Ruby methods
• Supports configurable serialization depth, PII filtering, and tracking of method arguments and return values
• Adds comprehensive test coverage for instrumentation features
• Provides example usage demonstrating instrumentation of instance and class methods
• Updates gemspec with new dependencies and Ruby version requirement

Changes

Core Functionality

• Added lib/observable/instrumenter.rb implementing the Instrumenter with:
  • Extraction of caller method and class information
  • Span creation with attributes for method name, namespace, file path, line number, arguments, and return values
  • PII filtering based on configurable regex patterns
  • Serialization of arguments and return values with depth limits
  • Exception capturing and span error status setting
• Updated lib/observable.rb to expose a convenience method for creating an instrumenter instance

Configuration

• Added Observable::Configuration using dry-configurable for:
  • Transport type, app namespace, attribute namespace
  • Tracer names and formatters
  • PII filters and max serialization depth
  • Option to track return values

Example and Tests

• Added example.rb demonstrating configuration and usage of the instrumenter
• Added test/instrumenter_test.rb with tests covering:
  • Instrumenter existence and basic instrumentation
  • Capturing method names and namespaces
  • Span creation and attribute verification
  • Argument capturing and return value tracking
  • Exception recording
  • Configuration overrides

Test Support

• Added support classes for span and trace persistence and querying in test/support/persistence
• Added test/support/tracing_test_helper.rb for OpenTelemetry test setup and span access
• Updated test/test_helper.rb to configure OpenTelemetry SDK for tests

Miscellaneous

• Updated observable.gemspec to:
  • Change summary and description to reflect new instrumentation features
  • Require Ruby >= 3.0.0
  • Add runtime dependencies on opentelemetry-sdk, dry-configurable, and dry-struct
  • Add development dependencies for testing and linting

Test plan

• All new tests in test/instrumenter_test.rb pass successfully
• Manual verification of example usage outputs and span creation
• Confirmed PII filtering and argument serialization behavior
• Verified exception capturing and span error status
• Ensured configuration options apply correctly

This PR lays the foundation for robust OpenTelemetry instrumentation in Ruby applications with flexible configuration and strong test coverage.

🌿 Generated by Terry

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📎 Task: https://www.terragonlabs.com/task/ab86460c-5aff-431c-a974-508e612c6b26