[SinitsynAndrey]

Description

The regression appeared after FastAPI 0.142 added opentelemetry-api as a dependency. As a result, applications can have the root opentelemetry namespace installed without installing opentelemetry.semconv.

HAS_OPENTELEMETRY was set when importing only the opentelemetry namespace succeeded. Importing the MQTT broker then eagerly loaded TelemetryMiddleware, which requires opentelemetry.semconv, and failed with ModuleNotFoundError.

The compatibility check now requires opentelemetry.semconv. MQTT remains importable when only the OpenTelemetry API is installed, while faststream[otel] continues to enable telemetry. A regression test covers this isolated-import case.

Type of change

• Bug fix (a non-breaking change that resolves an issue)

Checklist

• My code adheres to the style guidelines of this project (just lint shows no errors)
• I have conducted a self-review of my own code
• I have made the necessary changes to the documentation
• My changes do not generate any new warnings
• I have added tests to validate the effectiveness of my fix or the functionality of my new feature
• Both new and existing unit tests pass successfully on my local environment by running just test-coverage
• I have ensured that static analysis tests are passing by running just static-analysis
• I have included code examples to illustrate the modifications

[CLAassistant]

All committers have signed the CLA.