declarative config metrics delta

[SylvainJuge]

part of #1054

replaces #1058

[github-actions]

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[SylvainJuge]

[for reviewer] this (and below) a test refactor to use builder pattern to make test slightly more readable/maintainable.

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Reviewing files that changed from the base of the PR and between 4a836b2 and 89a79c8.

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• custom/src/main/resources/co/elastic/otel/config.yaml

📝 Walkthrough

Walkthrough

Configuration updates set temporality_preference: delta for the OTLP/HTTP metrics exporter, add a commented temporality_preference: delta entry for the disabled OTLP/gRPC exporter, and change the Java runtime telemetry emit_experimental_metrics/development value to an environment-driven boolean. A unit test now asserts the new temporality_preference JSON property. Smoke tests refactor container startup: the protected startTarget(...) was replaced by a public fluent TestTarget builder (testTarget(image)) with customize(...), withBaseEnvironmentVariables(...), and start(); test usages were updated accordingly.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@custom/src/main/resources/co/elastic/otel/config.yaml`:
- Around line 47-55: The temporality_preference under the otlp_http exporter is
hard-coded to "delta"; change it to read from the
OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE environment variable with a
default of "delta" (same ${VAR:-default} pattern used for endpoint and
headers_list) so users can override temporality to "cumulative" or "lowmemory";
update the temporality_preference setting in the otlp_http block accordingly.

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📥 Commits

Reviewing files that changed from the base of the PR and between 04bb692 and 212ca78.

📒 Files selected for processing (5)

• custom/src/main/resources/co/elastic/otel/config.yaml
• custom/src/test/java/co/elastic/otel/declarativeconfig/DefaultDeclarativeConfigTest.java
• smoke-tests/src/test/java/com/example/javaagent/smoketest/AppServerProvidersTest.java
• smoke-tests/src/test/java/com/example/javaagent/smoketest/SmokeTest.java
• smoke-tests/src/test/java/com/example/javaagent/smoketest/TestAppSmokeTest.java