feat(dotnet): Add OpenTelemetry support for distributed tracing and metrics

[reachanihere]

Summary

• Add opt-in OpenTelemetry instrumentation to the .NET SDK
• ActivitySource GitHub.Copilot.SDK for distributed tracing
• Meter GitHub.Copilot.SDK for metrics
• Follows OpenTelemetry GenAI Semantic Conventions

Features

Spans

Span Name	Description
copilot.session	Root span for a session
copilot.turn	Assistant turn lifecycle
copilot.tool_execution	Tool execution
copilot.subagent	Subagent execution
copilot.hook	Hook execution
copilot.inference	LLM inference call with token usage

Metrics

• copilot.tokens.input / copilot.tokens.output - Token counters
• copilot.cost.total - Cost counter
• copilot.tool_executions - Tool execution counter
• copilot.errors - Error counter
• copilot.duration - Duration histogram

Enabling Telemetry

Telemetry is disabled by default. Enable via:

// Option 1: AppContext switch
AppContext.SetSwitch("GitHub.Copilot.EnableOpenTelemetry", true);

// Option 2: Environment variable
// GITHUB_COPILOT_ENABLE_OPEN_TELEMETRY=true

Then configure OpenTelemetry:

services.AddOpenTelemetry()
    .WithTracing(t => t.AddSource("GitHub.Copilot.SDK"))
    .WithMetrics(m => m.AddMeter("GitHub.Copilot.SDK"));

Test plan

• Unit tests for all span types (all tests passing)

• Build succeeds with no warnings

• Created a simple console app to test the instrumentation. Real OpenTelemetry spans captured from a live Copilot CLI session with telemetry enabled via AppContext.SetSwitch("GitHub.Copilot.EnableOpenTelemetry", true):

  • copilot.turn - Turn lifecycle with copilot.session.id, copilot.turn.id, gen_ai.system
  • copilot.inference - LLM call with gen_ai.operation.name, gen_ai.response.model

  Attributes follow GenAI Semantic Conventions and integrate with any OpenTelemetry-compatible backend.

  

New files

• src/Telemetry/CopilotTelemetry.cs - Main telemetry class
• src/Telemetry/OpenTelemetryConstants.cs - Span/attribute constants
• src/Telemetry/SessionTelemetryTracker.cs - Event → span conversion
• test/TelemetryTests.cs - Unit tests

Closes #181

[Copilot]

Pull request overview

This PR adds opt-in OpenTelemetry instrumentation to the .NET SDK for distributed tracing and metrics, following OpenTelemetry GenAI Semantic Conventions.

Changes:

• Adds telemetry infrastructure with ActivitySource and Meter for spans and metrics
• Implements SessionTelemetryTracker to convert session events into OpenTelemetry spans
• Integrates telemetry tracking into the CopilotSession lifecycle
• Adds comprehensive unit tests (10 tests) for telemetry functionality
• Documents the observability features in README with examples

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
dotnet/src/Telemetry/CopilotTelemetry.cs	Main telemetry class providing ActivitySource, Meter, and metric recording methods with opt-in enable/disable logic
dotnet/src/Telemetry/OpenTelemetryConstants.cs	Defines constants for span names, attribute names, and metric names following GenAI semantic conventions
dotnet/src/Telemetry/SessionTelemetryTracker.cs	Converts session events to OpenTelemetry spans, managing lifecycle of session, turn, tool, subagent, hook, and inference activities
dotnet/src/Session.cs	Integrates telemetry tracker into session, instantiating it on construction and disposing on cleanup
dotnet/src/GitHub.Copilot.SDK.csproj	Adds OpenTelemetry.Api package reference and InternalsVisibleTo for test project
dotnet/test/TelemetryTests.cs	Comprehensive unit tests covering all major span types and telemetry scenarios
dotnet/README.md	Documents how to enable and configure OpenTelemetry, lists available spans and metrics, includes example trace

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[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

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