feat: add reactive command support for lettuce-4.0 instrumentation

[YaoYingLong]

Adds tracing support for Lettuce 4.0 reactive Redis commands.

The new instrumentation starts spans when reactive commands are dispatched and ends them when the underlying reactive command completes, fails, or is cancelled. It also preserves the parent context for reactive callbacks so spans created inside subscribers are linked to the original caller context.

[Copilot]

Pull request overview

This PR adds tracing for Lettuce 4.0 reactive Redis commands (RxJava-based com.lambdaworks.redis API). It complements the existing async and sync instrumentation in the lettuce-4.0 javaagent module. Spans are started when a reactive command is dispatched (ReactiveCommandDispatcher.call) and ended when the underlying ObservableCommand terminates (complete / cancel / completeExceptionally). The original caller context is stashed via COMMAND_CONTEXT_KEY and restored while terminal callbacks run, so spans created inside subscriber callbacks link to the caller's context.

The implementation closely mirrors the established async instrumentation in the same module (LettuceAsyncCommandInstrumentation) and the reactive instrumentation in lettuce-5.0. The flow is internally consistent: non-response commands (e.g. SHUTDOWN) are ended early in the dispatch advice, and the terminal advice's endReactiveCommand short-circuits for those to avoid double-ending; command-level errors are extracted from the command output, and cancellation optionally records the experimental lettuce.command.cancelled attribute. The context.makeCurrent() in the terminal advice is NPE-safe because the context is only stored when COMMAND_CONTEXT_KEY is present.

Changes:

• Add LettuceReactiveCommandsInstrumentation (instrument dispatcher constructor + call) and LettuceReactiveCommandInstrumentation (instrument ObservableCommand constructor + terminal methods), registered in LettuceInstrumentationModule.
• Add InstrumentationPoints.endReactiveCommand to finalize reactive spans, mapping output/throwable errors and recording cancellation.
• Add LettuceReactiveClientTest covering subscribers, lambdas, flux publishers, blocking/async subscribers, and no-span cases.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
LettuceReactiveCommandsInstrumentation.java	New instrumentation that stores caller context on the dispatcher and starts the span on call, restoring scope and ending non-response spans on exit.
LettuceReactiveCommandInstrumentation.java	New instrumentation that saves the span context on ObservableCommand and ends the span + restores parent context on terminal methods.
InstrumentationPoints.java	Adds endReactiveCommand to end reactive spans with error/cancellation handling.
LettuceInstrumentationModule.java	Registers the two new reactive instrumentations.
LettuceReactiveClientTest.java	New test suite for reactive command tracing, mirroring the lettuce-5.0 reactive tests.

[trask]

a couple of naming suggestions

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated no new comments.

[otelbot]

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