Add Step-03 example agent: add observability using tracing feature and LangFuse

[denis-domanskii]

Motivation and Context

Third step of the code agent example.

Breaking Changes

---

Type of the changes

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Tests improvement
• Refactoring

Checklist

• The pull request has a description of the proposed change
• I read the Contributing Guidelines before opening the pull request
• The pull request uses develop as the base branch
• Tests for the changes have been added
• All new and existing tests passed

Additional steps for pull requests adding a new feature

• An issue describing the proposed change exists
• The pull request includes a link to the issue
• The change was discussed and approved in the issue
• Docs have been added / updated

[github-actions]

Qodana for JVM

17217 new problems were found

Inspection name	Severity	Problems
Unused import directive	🔶 Warning	16213
Check Kotlin and Java source code coverage	🔶 Warning	991
Missing KDoc for public API declaration	🔶 Warning	11
If-Null return/break/... foldable to '?:'	◽️ Notice	2

@@ Code coverage @@
+ 72% total lines covered
15552 lines analyzed, 11219 lines covered
# Calculated according to the filters of your coverage tool

☁️ View the detailed Qodana report

Contact Qodana team

Contact us at [email protected]

• Or via our issue tracker: https://jb.gg/qodana-issue
• Or share your feedback: https://jb.gg/qodana-discussions

[github-actions]

Qodana for JVM

1162 new problems were found

Inspection name	Severity	Problems
Check Kotlin and Java source code coverage	🔶 Warning	1151
Missing KDoc for public API declaration	🔶 Warning	11

@@ Code coverage @@
+ 72% total lines covered
16731 lines analyzed, 12147 lines covered
# Calculated according to the filters of your coverage tool

☁️ View the detailed Qodana report

Contact Qodana team

Contact us at [email protected]

• Or via our issue tracker: https://jb.gg/qodana-issue
• Or share your feedback: https://jb.gg/qodana-discussions

[BLannoo]

Not much to say about this, the difference with step 02 seems just this right:

install(OpenTelemetry) {
        setVerbose(true) // Send full strings instead of HIDDEN placeholders
        addLangfuseExporter(
            traceAttributes = listOf(
                CustomAttribute("langfuse.session.id", System.getenv("LANGFUSE_SESSION_ID") ?: ""),
            )
        )
    }

And the README.md which seems correctly updated

And in this version the agent has the tagging issue, but this is fixed in develop. So just merging develop into it like I did in branch https://github.com/JetBrains/koog/tree/codeagent/step-03-observability-bruno should be all you need.