refactor(demo): use stock OtlpHttpSpanExporter, drop custom JSON marshaler

[sunilp]

Summary

Drops the custom JamjetOtlpJsonSpanExporter (~100 LOC) + OtlpJsonMarshaler (~80 LOC) in favor of the stock OtlpHttpSpanExporter from io.opentelemetry:opentelemetry-exporter-otlp — which Koog already pulls in transitively via agents-features-opentelemetry-jvm:0.8.0.

Mirrors jamjet-runtime-java PR #6 (Spring AI demo simplification).

Why now

The custom marshaler was needed because:

1. Published Koog 0.8.0 doesn't ship a JSON OTLP exporter.
2. The Java OTel SDK's OtlpHttpSpanExporter defaults to OTLP/protobuf, and JamJet's intake was JSON-only.

Both constraints fall away with jamjet-cloud PR #16, which added OTLP/protobuf intake at /v1/otlp/v1/traces (deployed to api.jamjet.dev 2026-05-08). So we drop the custom marshaler and just use the stock exporter at its default protobuf encoding.

What's left in JamjetCloudExporter.kt

The new file is wiring only:

@JvmOverloads
public fun OpenTelemetryConfig.addJamjetCloudExporter(
    apiKey: String? = null,
    apiUrl: String = "https://api.jamjet.dev",
    timeout: Duration = Duration.ofSeconds(10),
) {
    val key = apiKey ?: System.getenv("JAMJET_API_KEY")
        ?: error("JAMJET_API_KEY is missing. ...")

    addSpanExporter(
        OtlpHttpSpanExporter.builder()
            .setEndpoint("$apiUrl/v1/otlp/v1/traces")
            .addHeader("Authorization", "Bearer $key")
            .setTimeout(timeout)
            .build()
    )
}

Same public API (addJamjetCloudExporter(apiKey, apiUrl, timeout)). No HTTP client, no Jackson, no companion classes.

Verified

• mvnw clean compile clean (release 21)
• mvnw spring-boot:run boots in 1.0s; OpenAI client + Engram autoconfig + Koog OpenTelemetry feature all wire up cleanly; PreflightCheck fails at the Engram health check as expected without docker
• Confirmed via mvn dependency:tree that opentelemetry-exporter-otlp:1.49.0 is already on the classpath transitively — no new dep declared

Net diff

+94 / −246 (the rewrite of JamjetCloudExporter.kt accounts for most of it).

File	Change
cloud/JamjetCloudExporter.kt	Drop JamjetOtlpJsonSpanExporter + OtlpJsonMarshaler; keep only addJamjetCloudExporter extension built around OtlpHttpSpanExporter
pom.xml	Description + dep comment update only — no dep changes
README.md	"OTLP/JSON" → "OTLP/HTTP-protobuf" mentions; ~50 LOC claim instead of 150
MemoryAgent.kt	Comment update

Followups

• Open the upstream Koog YouTrack issue contributing addJamjetCloudExporter as ai.koog.agents.features.opentelemetry.integration.jamjet.addJamjetCloudExporter (mirrors addDatadogExporter). Draft text saved at /tmp/koog_youtrack_issue.md in the working session.
• Demo end-to-end against real OPENAI + JAMJET keys + Engram via docker, confirm trace appears at cloud.jamjet.dev/dashboard/graph tagged service.name=kotlin-koog-engram-demo (CI doesn't have OpenAI access, so this is manual)

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 9d96ad37-99ea-4113-b4bd-a556b8451e1b

📥 Commits

Reviewing files that changed from the base of the PR and between 6fdf4d2 and 2a847cb.

📒 Files selected for processing (4)

• examples/kotlin-koog-engram-cloud-demo/README.md
• examples/kotlin-koog-engram-cloud-demo/pom.xml
• examples/kotlin-koog-engram-cloud-demo/src/main/kotlin/dev/jamjet/demo/koogengram/MemoryAgent.kt
• examples/kotlin-koog-engram-cloud-demo/src/main/kotlin/dev/jamjet/demo/koogengram/cloud/JamjetCloudExporter.kt

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/kotlin-koog-stock-otlp

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