Clear stale sidecar/record on ThreadContext init, fix contextattribute= no-op

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: jbachorik

ddprof-lib/src/main/java/com/datadoghq/profiler/ThreadContext.java

@@ -100,6 +100,16 @@ public ThreadContext(ByteBuffer recordBuffer, ByteBuffer tlsPtrBuffer, ByteBuffe
             throw new UnsupportedOperationException(
                 "ByteBuffer context path requires little-endian platform");
         }
+        // Zero sidecar + record to prevent stale encodings from a previous profiler session.
+        // The native ProfiledThread survives across sessions, so the sidecar may hold
+        // old tag encodings and the record may hold old attrs_data.
+        for (int i = 0; i < MAX_CUSTOM_SLOTS; i++) {
+            this.sidecarBuffer.putInt(i * 4, 0);
+        }
+        this.sidecarBuffer.putLong(this.lrsSidecarOffset, 0);
+        this.recordBuffer.put(this.validOffset, (byte) 0);
+        this.recordBuffer.putShort(this.attrsDataSizeOffset, (short) 0);
+        this.tlsPtrBuffer.putLong(0, 0);
     }
 
     /**

ddprof-test/src/test/java/com/datadoghq/profiler/context/OtelContextStorageModeTest.java

@@ -63,7 +63,7 @@ public void cleanup() {
     public void testOtelStorageModeContext() throws Exception {
         Path jfrFile = Files.createTempFile("otel-ctx-otel", ".jfr");
 
-        profiler.execute(String.format("start,cpu=1ms,jfr,file=%s", jfrFile.toAbsolutePath()));
+        profiler.execute(String.format("start,cpu=1ms,attributes=tag1;tag2;tag3,jfr,file=%s", jfrFile.toAbsolutePath()));
         profilerStarted = true;
 
         long localRootSpanId = 0x1111222233334444L;
@@ -84,7 +84,7 @@ public void testOtelStorageModeContext() throws Exception {
     public void testOtelModeStartsOnAnyPlatform() throws Exception {
         Path jfrFile = Files.createTempFile("otel-ctx-any", ".jfr");
 
-        profiler.execute(String.format("start,cpu=1ms,jfr,file=%s", jfrFile.toAbsolutePath()));
+        profiler.execute(String.format("start,cpu=1ms,attributes=tag1;tag2;tag3,jfr,file=%s", jfrFile.toAbsolutePath()));
         profilerStarted = true;
 
         // Context operations should not crash
@@ -98,7 +98,7 @@ public void testOtelModeStartsOnAnyPlatform() throws Exception {
     public void testOtelModeClearContext() throws Exception {
         Path jfrFile = Files.createTempFile("otel-ctx-clear", ".jfr");
 
-        profiler.execute(String.format("start,cpu=1ms,jfr,file=%s", jfrFile.toAbsolutePath()));
+        profiler.execute(String.format("start,cpu=1ms,attributes=tag1;tag2;tag3,jfr,file=%s", jfrFile.toAbsolutePath()));
         profilerStarted = true;
 
         profiler.setContext(0xCAFEBABEL, 0xDEADBEEFL, 0L, 0x12345678L);
@@ -117,7 +117,7 @@ public void testOtelModeClearContext() throws Exception {
     public void testOtelModeCustomAttributes() throws Exception {
         Path jfrFile = Files.createTempFile("otel-ctx-attrs", ".jfr");
 
-        profiler.execute(String.format("start,cpu=1ms,contextattribute=http.route;db.system,jfr,file=%s", jfrFile.toAbsolutePath()));
+        profiler.execute(String.format("start,cpu=1ms,attributes=http.route;db.system,jfr,file=%s", jfrFile.toAbsolutePath()));
         profilerStarted = true;
 
         // Register attribute keys
@@ -146,7 +146,7 @@ public void testOtelModeCustomAttributes() throws Exception {
     public void testSetContextAttribute() throws Exception {
         Path jfrFile = Files.createTempFile("otel-ctx-attr", ".jfr");
 
-        profiler.execute(String.format("start,cpu=1ms,contextattribute=http.route,jfr,file=%s", jfrFile.toAbsolutePath()));
+        profiler.execute(String.format("start,cpu=1ms,attributes=http.route,jfr,file=%s", jfrFile.toAbsolutePath()));
         profilerStarted = true;
 
         profiler.setContext(0x456L, 0x123L, 0L, 0x789L);
@@ -163,7 +163,7 @@ public void testSetContextAttribute() throws Exception {
     public void testOtelModeAttributeOverflow() throws Exception {
         Path jfrFile = Files.createTempFile("otel-ctx-overflow", ".jfr");
 
-        profiler.execute(String.format("start,cpu=1ms,contextattribute=k0;k1;k2;k3;k4,jfr,file=%s", jfrFile.toAbsolutePath()));
+        profiler.execute(String.format("start,cpu=1ms,attributes=k0;k1;k2;k3;k4,jfr,file=%s", jfrFile.toAbsolutePath()));
         profilerStarted = true;
 
         OTelContext.getInstance().registerAttributeKeys("k0", "k1", "k2", "k3", "k4");