Add --otel distributed tracing support

[mkrueger]

Summary

Adds distributed tracing to CosmosShell so requests carry a sampled W3C traceparent that external tracing systems (for example, the Cosmos DB emulator) can use to correlate shell activity. Optionally exports spans over OTLP.

This addresses the distributed-tracing request. File-based diagnostic logging (issue #122) is intentionally out of scope and will follow in a separate PR.

How it works

The Cosmos SDK only emits a traceparent with the sampled flag set (-01) when two things are true: the Azure SDK Azure.Experimental.EnableActivitySource switch is on, and a recorded (sampled) Activity is in scope. This PR wires both up:

• Sets AppContext switch Azure.Experimental.EnableActivitySource before any CosmosClient is created.
• Registers an OpenTelemetry TracerProvider with AlwaysOnSampler, listening to the Azure.Cosmos.Operation and CosmosDBShell activity sources, so activities are recorded.
• Wraps each shell command in a CosmosDBShell root activity, so every command is one trace.
• Sets CosmosClientTelemetryOptions.DisableDistributedTracing = false explicitly.

CLI

New --otel [endpoint] option (optional value, mirroring --mcp):

• --otel — enable tracing (always emits a sampled traceparent). Spans are exported only if an OTLP endpoint is configured (see below); otherwise tracing is local-only with no export.
• --otel <endpoint> — also export spans to that explicit OTLP endpoint.
• When --otel is given without an endpoint, the endpoint falls back to the standard OTEL_EXPORTER_OTLP_ENDPOINT environment variable; if that is also unset, no spans are exported.

A malformed endpoint (from --otel <endpoint> or OTEL_EXPORTER_OTLP_ENDPOINT) now produces a clean error and a non-zero exit code instead of an unhandled exception.

Changes

• --otel option + plumbing in Program.cs; help-Otel and otel-error-invalid-endpoint in en.ftl.
• New Core/TracingBootstrap.cs (provider lifecycle + per-command activity source).
• ShellInterpreter: enable SDK tracing, per-command root activity.
• OpenTelemetry + OTLP exporter packages (1.15.3, the patched version clearing advisory NU1902).
• README, docs/navigation.md, and Runtime/TracingBootstrapTests.cs.

Validation

• Main project build: 0 warnings, 0 errors.
• Full test suite: 1293 passed, 0 failed, 74 skipped (pre-existing emulator-dependent skips).

Out of scope

File logging / issue #122, OTEL metrics & logs signals, Azure Monitor / App Insights exporters, Direct-mode traceparent specifics.

[Copilot]

Pull request overview

Adds optional OpenTelemetry-based distributed tracing to CosmosDBShell via a new --otel [endpoint] startup option, enabling sampled W3C traceparent propagation on Cosmos SDK requests and (optionally) OTLP span export.

Changes:

• Adds --otel [endpoint] CLI option, wiring initialization/disposal of tracing in Program.cs and help text in en.ftl.
• Introduces TracingBootstrap to configure an OpenTelemetry TracerProvider and create per-command root activities.
• Updates docs/README and adds unit tests covering tracing bootstrap behavior.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
README.md	Documents the new --otel option in the feature list and options table.
docs/navigation.md	Adds --otel and OTEL_EXPORTER_OTLP_ENDPOINT to navigation docs + examples.
Directory.Packages.props	Pins OpenTelemetry + OTLP exporter package versions.
CosmosDBShell/Program.cs	Parses --otel [endpoint], initializes/disposes tracing, and adds the option to help output.
CosmosDBShell/lang/en.ftl	Adds localized help text for --otel.
CosmosDBShell/CosmosDBShell.csproj	Adds package references for OpenTelemetry and the OTLP exporter.
CosmosDBShell/Azure.Data.Cosmos.Shell.Core/TracingBootstrap.cs	New tracing bootstrapper (provider lifecycle + ActivitySource root activities).
CosmosDBShell/Azure.Data.Cosmos.Shell.Core/ShellInterpreter.cs	Wraps each executed command in a tracing activity; enables Cosmos SDK distributed tracing option.
CosmosDBShell.Tests/Runtime/TracingBootstrapTests.cs	Adds tests verifying activity creation/recording and the Azure SDK switch.