test(reader): use Arena.ofAuto() over Arena.global() in decoder tests

Arena.global() never frees; ofAuto() is GC-backed and matches the
VarBinView test in the same series.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: dfa1

reader/src/test/java/io/github/dfa1/vortex/reader/decode/AlpEncodingDecoderTest.java

@@ -69,7 +69,7 @@ void decode_nonPrimitiveDtype_throws() {
         ArrayNode node = ArrayNode.of(EncodingId.VORTEX_ALP, ByteBuffer.wrap(new ALPMetadata(0, 0, null).encode()),
                 new ArrayNode[0], new int[0]);
         DecodeContext ctx = new DecodeContext(node, new DType.Utf8(false), 1,
-                new MemorySegment[0], REGISTRY, Arena.global());
+                new MemorySegment[0], REGISTRY, Arena.ofAuto());
 
         // When / Then
         assertThatThrownBy(() -> SUT.decode(ctx)).hasMessageContaining("expected primitive dtype");
@@ -80,7 +80,7 @@ void decode_missingMetadata_defaultsToZeroExponents() {
         // Given no metadata — decoder falls back to exp_e=0, exp_f=0 (scale 1.0)
         ArrayNode enc = ArrayNode.of(EncodingId.VORTEX_PRIMITIVE, null, new ArrayNode[0], new int[]{0});
         ArrayNode node = ArrayNode.of(EncodingId.VORTEX_ALP, null, new ArrayNode[]{enc}, new int[0]);
-        DecodeContext ctx = new DecodeContext(node, F64, 2, new MemorySegment[]{leLongs(5L, 7L)}, REGISTRY, Arena.global());
+        DecodeContext ctx = new DecodeContext(node, F64, 2, new MemorySegment[]{leLongs(5L, 7L)}, REGISTRY, Arena.ofAuto());
 
         // When
         DoubleArray result = (DoubleArray) SUT.decode(ctx);
@@ -97,7 +97,7 @@ void decode_f64_broadcastNoPatches_returnsConstant() {
         ArrayNode enc = ArrayNode.of(EncodingId.VORTEX_PRIMITIVE, null, new ArrayNode[0], new int[]{0});
         byte[] meta = new ALPMetadata(2, 0, null).encode(); // exp_e=2 -> *0.01
         ArrayNode node = ArrayNode.of(EncodingId.VORTEX_ALP, ByteBuffer.wrap(meta), new ArrayNode[]{enc}, new int[0]);
-        DecodeContext ctx = new DecodeContext(node, F64, 4, new MemorySegment[]{leLongs(123L)}, REGISTRY, Arena.global());
+        DecodeContext ctx = new DecodeContext(node, F64, 4, new MemorySegment[]{leLongs(123L)}, REGISTRY, Arena.ofAuto());
 
         // When
         DoubleArray result = (DoubleArray) SUT.decode(ctx);
@@ -115,7 +115,7 @@ void decode_f32_broadcastNoPatches_returnsConstant() {
         ArrayNode enc = ArrayNode.of(EncodingId.VORTEX_PRIMITIVE, null, new ArrayNode[0], new int[]{0});
         byte[] meta = new ALPMetadata(1, 0, null).encode(); // exp_e=1 -> *0.1
         ArrayNode node = ArrayNode.of(EncodingId.VORTEX_ALP, ByteBuffer.wrap(meta), new ArrayNode[]{enc}, new int[0]);
-        DecodeContext ctx = new DecodeContext(node, F32, 3, new MemorySegment[]{leInts(25)}, REGISTRY, Arena.global());
+        DecodeContext ctx = new DecodeContext(node, F32, 3, new MemorySegment[]{leInts(25)}, REGISTRY, Arena.ofAuto());
 
         // When
         FloatArray result = (FloatArray) SUT.decode(ctx);
@@ -142,7 +142,7 @@ void decode_f64_patches_withU8Indices() {
 
         MemorySegment idxSeg = MemorySegment.ofArray(new byte[]{1}); // patch row 1
         MemorySegment[] segs = {leLongs(100L, 0L, 300L), idxSeg, leDoubles(9.0)};
-        DecodeContext ctx = new DecodeContext(node, F64, 3, segs, REGISTRY, Arena.global());
+        DecodeContext ctx = new DecodeContext(node, F64, 3, segs, REGISTRY, Arena.ofAuto());
 
         // When
         DoubleArray result = (DoubleArray) SUT.decode(ctx);
@@ -166,7 +166,7 @@ void decode_patches_nonUnsignedIndexPtype_throws() {
                 new ArrayNode[]{enc, idx, val}, new int[0]);
 
         MemorySegment[] segs = {leLongs(100L, 0L), leInts(1), leDoubles(9.0)};
-        DecodeContext ctx = new DecodeContext(node, F64, 2, segs, REGISTRY, Arena.global());
+        DecodeContext ctx = new DecodeContext(node, F64, 2, segs, REGISTRY, Arena.ofAuto());
 
         // When / Then
         assertThatThrownBy(() -> SUT.decode(ctx)).hasMessageContaining("non-unsigned patch index ptype");

reader/src/test/java/io/github/dfa1/vortex/reader/decode/DateTimePartsEncodingDecoderTest.java

@@ -48,7 +48,7 @@ private static DecodeContext ctx(ByteBuffer meta, DType dtype, long n,
         ArrayNode s = ArrayNode.of(EncodingId.VORTEX_PRIMITIVE, null, new ArrayNode[0], new int[]{1});
         ArrayNode ss = ArrayNode.of(EncodingId.VORTEX_PRIMITIVE, null, new ArrayNode[0], new int[]{2});
         ArrayNode node = ArrayNode.of(EncodingId.VORTEX_DATETIMEPARTS, meta, new ArrayNode[]{d, s, ss}, new int[0]);
-        return new DecodeContext(node, dtype, n, new MemorySegment[]{days, seconds, subseconds}, REGISTRY, Arena.global());
+        return new DecodeContext(node, dtype, n, new MemorySegment[]{days, seconds, subseconds}, REGISTRY, Arena.ofAuto());
     }
 
     @Test
@@ -62,7 +62,7 @@ void decode_missingMetadata_throws() {
         // Given a node with no metadata
         ArrayNode node = ArrayNode.of(EncodingId.VORTEX_DATETIMEPARTS, null, new ArrayNode[0], new int[0]);
         DecodeContext c = new DecodeContext(node, timestampDType(TimeUnit.Milliseconds, false), 1,
-                new MemorySegment[0], REGISTRY, Arena.global());
+                new MemorySegment[0], REGISTRY, Arena.ofAuto());
 
         // When / Then
         assertThatThrownBy(() -> SUT.decode(c)).hasMessageContaining("missing metadata");

reader/src/test/java/io/github/dfa1/vortex/reader/decode/DeltaEncodingDecoderTest.java

@@ -40,7 +40,7 @@ void decode_nullMetadata_returnsEmptyArray(PType ptype) {
         // always writes metadata)
         ArrayNode node = ArrayNode.of(EncodingId.FASTLANES_DELTA, null, new ArrayNode[0], new int[0]);
         DecodeContext ctx = new DecodeContext(node, new DType.Primitive(ptype, false), 0,
-                new MemorySegment[0], REGISTRY, Arena.global());
+                new MemorySegment[0], REGISTRY, Arena.ofAuto());
 
         // When
         Array result = SUT.decode(ctx);
@@ -65,7 +65,7 @@ void decode_constantChildren_broadcastsAcrossChunk() {
 
         // one element each → broadcast
         MemorySegment[] segs = {TestSegments.leLongs(0L), TestSegments.leLongs(0L)};
-        DecodeContext ctx = new DecodeContext(node, new DType.Primitive(ptype, false), 4, segs, REGISTRY, Arena.global());
+        DecodeContext ctx = new DecodeContext(node, new DType.Primitive(ptype, false), 4, segs, REGISTRY, Arena.ofAuto());
 
         // When
         LongArray result = (LongArray) SUT.decode(ctx);
@@ -89,15 +89,15 @@ void decode_constantBases_nonZeroOffsetAndBase() {
         ArrayNode node = ArrayNode.of(EncodingId.FASTLANES_DELTA, meta, new ArrayNode[]{bases, deltas}, new int[0]);
 
         MemorySegment[] segs = {TestSegments.leLongs(5L), TestSegments.leLongs(0L)};
-        DecodeContext ctx = new DecodeContext(node, new DType.Primitive(ptype, false), 3, segs, REGISTRY, Arena.global());
+        DecodeContext ctx = new DecodeContext(node, new DType.Primitive(ptype, false), 3, segs, REGISTRY, Arena.ofAuto());
 
         // When
         LongArray result = (LongArray) SUT.decode(ctx);
 
         // Then prefix-sum of zero deltas over base 5 stays 5 on lane 0
         assertThat(result.getLong(0)).isEqualTo(5L);
         // sanity: materialized bytes are little-endian
-        MemorySegment seg = result.materialize(Arena.global());
+        MemorySegment seg = result.materialize(Arena.ofAuto());
         assertThat(seg.get(PTypeIO.LE_LONG, 0)).isEqualTo(5L);
     }
 }

reader/src/test/java/io/github/dfa1/vortex/reader/decode/VarBinEncodingDecoderTest.java

@@ -56,7 +56,7 @@ void decode_broadcastOffsets_singleOffsetExpandsToAllRows() {
         // Given an offsets child holding a single value (as ConstantEncoding emits):
         // capacity 1 < n+1, so the decoder must broadcast-copy it. A constant offset
         // means every row spans an empty slice.
-        MemorySegment data = Arena.global().allocate(1);
+        MemorySegment data = Arena.ofAuto().allocate(1);
         MemorySegment offsets = TestSegments.leInts(0); // one element only
 
         // When

reader/src/test/java/io/github/dfa1/vortex/reader/decode/ZigZagEncodingDecoderTest.java

@@ -30,7 +30,7 @@ class ZigZagEncodingDecoderTest {
     // --- zigzag encode helpers (mirror of the decoder's (u >>> 1) ^ -(u & 1)) ---
 
     private static MemorySegment encodedBytes(byte... signed) {
-        MemorySegment seg = Arena.global().allocate(signed.length);
+        MemorySegment seg = Arena.ofAuto().allocate(signed.length);
         for (int i = 0; i < signed.length; i++) {
             seg.set(ValueLayout.JAVA_BYTE, i, (byte) ((signed[i] << 1) ^ (signed[i] >> 7)));
         }