fix(kafka): [Queue Instrumentation 31] Write enqueued-time header as plain decimal

The sentry-task-enqueued-time Kafka header was serialized via
String.valueOf(double), which emits scientific notation (e.g.
1.776933649613E9) for epoch-seconds values. Cross-SDK consumers
(sentry-python, -ruby, -php, -dotnet) expect a plain decimal like
1776938295.692000 and could not parse the Java output, defeating the
cross-SDK alignment goal of #5283.

Route the value through DateUtils.doubleToBigDecimal(...).toString(),
the same helper already used to serialize epoch-seconds timestamps in
SentryTransaction, SentrySpan, SentryLogEvent, etc. At the pinned scale
of 6, BigDecimal.toString() produces plain decimal form for all
realistic epoch-seconds magnitudes.

Add regression assertions that reject scientific notation and pin the
plain-decimal format in SentryKafkaProducerInterceptorTest.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: adinauer

sentry-kafka/src/main/java/io/sentry/kafka/SentryKafkaProducerInterceptor.java

@@ -128,7 +128,8 @@ private void injectHeaders(final @NotNull Headers headers, final @NotNull ISpan
     headers.remove(SENTRY_ENQUEUED_TIME_HEADER);
     headers.add(
         SENTRY_ENQUEUED_TIME_HEADER,
-        String.valueOf(DateUtils.millisToSeconds(System.currentTimeMillis()))
+        DateUtils.doubleToBigDecimal(DateUtils.millisToSeconds(System.currentTimeMillis()))
+            .toString()
             .getBytes(StandardCharsets.UTF_8));
   }
 

sentry-kafka/src/test/kotlin/io/sentry/kafka/SentryKafkaProducerInterceptorTest.kt

@@ -17,6 +17,7 @@ import kotlin.test.AfterTest
 import kotlin.test.BeforeTest
 import kotlin.test.Test
 import kotlin.test.assertEquals
+import kotlin.test.assertFalse
 import kotlin.test.assertNotNull
 import kotlin.test.assertSame
 import kotlin.test.assertTrue
@@ -84,7 +85,19 @@ class SentryKafkaProducerInterceptorTest {
     val enqueuedTimeHeader =
       record.headers().lastHeader(SentryKafkaProducerInterceptor.SENTRY_ENQUEUED_TIME_HEADER)
     assertNotNull(enqueuedTimeHeader)
-    val enqueuedTime = String(enqueuedTimeHeader.value(), StandardCharsets.UTF_8).toDouble()
+    val enqueuedTimeRaw = String(enqueuedTimeHeader.value(), StandardCharsets.UTF_8)
+    // Must be written as a plain decimal so cross-SDK consumers (e.g. sentry-python) can
+    // parse it. String.valueOf(double) would emit scientific notation (e.g. 1.77E9) for
+    // epoch seconds.
+    assertFalse(
+      enqueuedTimeRaw.contains('E') || enqueuedTimeRaw.contains('e'),
+      "enqueued-time header must not use scientific notation, got: $enqueuedTimeRaw",
+    )
+    assertTrue(
+      enqueuedTimeRaw.matches(Regex("""^\d+\.\d{6}$""")),
+      "enqueued-time header must be plain epoch seconds with 6 decimals, got: $enqueuedTimeRaw",
+    )
+    val enqueuedTime = enqueuedTimeRaw.toDouble()
     assertTrue(enqueuedTime > 0)
   }