Add OpenTelemetry logging backend

[alexander-yevsyukov]

Summary

The OpenTelemetry logging backend — the OTel half of the branch split. The config
sync and version bump live in #142 (update-config → master). The original 9 OTel
commits are preserved here.

Base: this PR is stacked on update-config (not master).

Contents

• otel-backend (KMP) — maps Spine LogData to OTel log records: severity
  mapping, attribute mapping (incl. repeated values and the tag. namespace),
  log-site code.* attributes, event-name routing, and span correlation.
• otel-backend-bootstrap (JVM) — OtelLogging install helpers (OTLP/HTTP and
  from-environment) returning an AutoCloseable.
• OpenTelemetryKotlin dependency declaration (opentelemetry-kotlin 0.4.0).
• Docs: docs/otel-backend.md, the module README, and a README backends entry.

Verification

./gradlew build dokkaGenerate is green; otel-backend:jvmTest and
otel-backend-bootstrap:test pass. The dependency report includes the OTel deps.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds an OpenTelemetry (OTel) logging backend to Spine Logging, mapping LogData to OTel log records (including severity, attributes, log-site code.*, tags, and span correlation) and providing a small JVM bootstrap module for turnkey OTLP/HTTP wiring.

Changes:

• Introduces otel-backend (KMP module, JVM target) with LogData → Logger.emit(...) mapping and a log-based events API (logEvent / EVENT_NAME).
• Adds otel-backend-bootstrap (JVM module) to install an OTLP/HTTP pipeline and manage SDK lifecycle via AutoCloseable.
• Updates build/publishing wiring, docs, and aligns existing backends on a shared logger-name convention ($ → .).

Reviewed changes

Copilot reviewed 29 out of 31 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
settings.gradle.kts	Renames root project and includes the new OTel backend modules.
README.md	Updates project status messaging and documents the OTel backend entry.
logging/src/commonMain/kotlin/io/spine/logging/backend/BackendFactory.kt	Adds shared loggerName() helper for consistent backend logger naming.
docs/otel-backend.md	New guide describing setup, mapping, and events for the OTel backend.
docs/dependencies/pom.xml	Refreshes dependency report to include OTel Kotlin artifacts and related deps.
buildSrc/src/main/kotlin/io/spine/dependency/lib/OpenTelemetryKotlin.kt	Adds centralized dependency coordinates for opentelemetry-kotlin (0.4.0).
build.gradle.kts	Adds otel-backend-bootstrap to published modules list.
backends/otel-backend/src/jvmTest/kotlin/io/spine/logging/backend/otel/OtelLoggerBackendSpec.kt	Adds JVM tests covering mapping behavior, events, and span correlation.
backends/otel-backend/src/jvmTest/kotlin/io/spine/logging/backend/otel/given/StubMetadata.kt	Test fixture for mutable Metadata.
backends/otel-backend/src/jvmTest/kotlin/io/spine/logging/backend/otel/given/StubLogSite.kt	Test fixture for LogSite.
backends/otel-backend/src/jvmTest/kotlin/io/spine/logging/backend/otel/given/StubLogData.kt	Test fixture for mutable LogData.
backends/otel-backend/src/jvmTest/kotlin/io/spine/logging/backend/otel/given/RecordingLogRecordProcessor.kt	Test processor to capture emitted OTel log records.
backends/otel-backend/src/jvmTest/kotlin/io/spine/logging/backend/otel/given/NoOpSpanProcessor.kt	Test span processor to enable valid span contexts for correlation tests.
backends/otel-backend/src/jvmMain/kotlin/io/spine/logging/backend/otel/OtelBackendFactory.kt	JVM BackendFactory registered via @AutoService / KSP.
backends/otel-backend/src/commonMain/kotlin/io/spine/logging/backend/otel/SeverityMapping.kt	Implements Level → SeverityNumber threshold mapping.
backends/otel-backend/src/commonMain/kotlin/io/spine/logging/backend/otel/OtelLoggerBackend.kt	Implements the core LoggerBackend mapping and error handling.
backends/otel-backend/src/commonMain/kotlin/io/spine/logging/backend/otel/OtelEvents.kt	Adds EVENT_NAME metadata key and WithLogging.logEvent(...) helper.
backends/otel-backend/src/commonMain/kotlin/io/spine/logging/backend/otel/OtelBackendSettings.kt	Adds injectable global OpenTelemetry instance holder (defaults to noop).
backends/otel-backend/src/commonMain/kotlin/io/spine/logging/backend/otel/AttributeMapping.kt	Implements metadata/tags/log-site → OTel attributes mapping.
backends/otel-backend/README.md	Module README linking to the full OTel backend guide.
backends/otel-backend/build.gradle.kts	Configures KMP module deps, publishing, and JVM test task setup (JUnit Platform).
backends/otel-backend-bootstrap/src/test/kotlin/io/spine/logging/backend/otel/bootstrap/OtelLoggingSpec.kt	Adds tests for endpoint resolution and install/shutdown path.
backends/otel-backend-bootstrap/src/main/kotlin/io/spine/logging/backend/otel/bootstrap/OtelLogging.kt	Adds OTLP/HTTP bootstrap installer with shutdown handling and warning-on-failure.
backends/otel-backend-bootstrap/build.gradle.kts	Configures bootstrap module dependencies (SDK + exporters + coroutines).
backends/log4j2-backend/src/main/kotlin/io/spine/logging/backend/log4j2/Log4j2BackendFactory.kt	Switches to shared BackendFactory.loggerName() convention.
backends/jul-backend/src/main/kotlin/io/spine/logging/backend/jul/JulBackendFactory.kt	Switches to shared BackendFactory.loggerName() convention.
backends/jul-backend/src/main/kotlin/io/spine/logging/backend/jul/JulBackend.kt	Updates KDoc to reflect logger-name derivation now handled in the factory.
backends/jul-backend/src/main/kotlin/io/spine/logging/backend/jul/AbstractJulBackend.kt	Removes redundant $ → . conversion (now done by factories).
.agents/tasks/otel-backend-report.md	Adds internal research/spec document for the OTel backend work.
.agents/tasks/otel-backend-implementation.md	Adds internal implementation plan / execution log for the OTel backend work.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 4c59160d53

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[codecov]

Codecov Report

❌ Patch coverage is 88.98305% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 17.67%. Comparing base (8bd4485) to head (f2f6cff).

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #143      +/-   ##
============================================
+ Coverage     14.20%   17.67%   +3.46%     
- Complexity      120      149      +29     
============================================
  Files           102      109       +7     
  Lines          2443     2558     +115     
  Branches        379      404      +25     
============================================
+ Hits            347      452     +105     
- Misses         2065     2068       +3     
- Partials         31       38       +7     

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.