refactor(reader): UnknownArray carries the typed EncodingId

String encodingId predated the sealed EncodingId — a closed enum
could not represent an unknown id, so the raw string was the only
option. Now the component is typed: a Custom, or a WellKnown whose
decoder is not registered.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: dfa1

reader/src/main/java/io/github/dfa1/vortex/reader/ReadRegistry.java

@@ -99,7 +99,6 @@ public MemorySegment decodeAsSegment(DecodeContext ctx) {
     }
 
     private static UnknownArray decodeUnknown(DecodeContext ctx, ArrayNode node) {
-        String rawId = node.encodingId().id();
         MemorySegment[] bufs = new MemorySegment[node.bufferIndices().length];
         for (int i = 0; i < bufs.length; i++) {
             bufs[i] = ctx.buffer(i);
@@ -113,7 +112,7 @@ private static UnknownArray decodeUnknown(DecodeContext ctx, ArrayNode node) {
             children[i] = decodeUnknown(childCtx, childNode);
         }
         return new UnknownArray(
-                rawId, ctx.dtype(), ctx.rowCount(),
+                node.encodingId(), ctx.dtype(), ctx.rowCount(),
                 node.metadata(), bufs, children);
     }
 

reader/src/main/java/io/github/dfa1/vortex/reader/array/UnknownArray.java

@@ -1,6 +1,7 @@
 package io.github.dfa1.vortex.reader.array;
 
 import io.github.dfa1.vortex.core.model.DType;
+import io.github.dfa1.vortex.core.model.EncodingId;
 import io.github.dfa1.vortex.core.error.VortexException;
 
 import java.lang.foreign.MemorySegment;
@@ -15,15 +16,15 @@
 /// Constructed by `Registry` when `allowUnknown()` is set and an encoding id is not
 /// in the registry. Data access beyond `buffer(i)` and `child(i)` is not supported.
 ///
-/// @param encodingId the unrecognized encoding id string
+/// @param encodingId the unrecognized encoding id — a [EncodingId.Custom], or a [EncodingId.WellKnown] with no registered decoder
 /// @param dtype      logical type of the array
 /// @param length     number of logical rows
 /// @param metadata   raw encoding metadata bytes, or `null`
 /// @param buffers    raw data buffers owned by this node
 /// @param children   decoded child arrays (also wrapped as unknown)
 @SuppressWarnings("java:S6218") // internal data carrier; record components are arrays of immutable primitives or refs that flow through pipelines without ever being compared.
 public record UnknownArray(
-        String encodingId,
+        EncodingId encodingId,
         DType dtype,
         long length,
         MemorySegment metadata,

reader/src/test/java/io/github/dfa1/vortex/reader/ReadRegistryTest.java

@@ -64,7 +64,7 @@ void decodeKnownEncodingWithoutDecoderReturnsUnknownArrayWhenAllowed() {
 
         // Then
         assertThat(result).isInstanceOf(UnknownArray.class);
-        assertThat(((UnknownArray) result).encodingId()).isEqualTo("vortex.primitive");
+        assertThat(((UnknownArray) result).encodingId()).isEqualTo(EncodingId.VORTEX_PRIMITIVE);
     }
 
     @Test
@@ -85,7 +85,7 @@ void decodeUnknownEncodingReturnsUnknownArrayWhenAllowed() {
         // Then
         assertThat(result).isInstanceOf(UnknownArray.class);
         UnknownArray unknown = (UnknownArray) result;
-        assertThat(unknown.encodingId()).isEqualTo("some.unknown");
+        assertThat(unknown.encodingId()).isEqualTo(new EncodingId.Custom("some.unknown"));
         assertThat(unknown.dtype()).isEqualTo(DTypes.I32);
         assertThat(unknown.length()).isEqualTo(5L);
         assertThat(unknown.metadata()).isEqualTo(metadata);
@@ -114,7 +114,7 @@ void decodeUnknownEncodingWrapsChildrenAsUnknown() {
         UnknownArray unknown = (UnknownArray) result;
         assertThat(unknown.children()).hasSize(1);
         assertThat(unknown.children()[0]).isInstanceOf(UnknownArray.class);
-        assertThat(((UnknownArray) unknown.children()[0]).encodingId()).isEqualTo("vortex.primitive");
+        assertThat(((UnknownArray) unknown.children()[0]).encodingId()).isEqualTo(EncodingId.VORTEX_PRIMITIVE);
         assertThat(sut.isAllowUnknown()).isTrue();
     }
 

reader/src/test/java/io/github/dfa1/vortex/reader/VortexReaderTest.java

@@ -40,7 +40,7 @@ public EncodingId encodingId() {
                 public Array decode(DecodeContext ctx) {
                     // Generic zero-length stand-in: scan chunk row count comes from the
                     // layout, so the leaf array's contents are irrelevant to this test.
-                    return new UnknownArray("stub", ctx.dtype(), 0, null,
+                    return new UnknownArray(EncodingId.parse("stub"), ctx.dtype(), 0, null,
                             new MemorySegment[0], new Array[0]);
                 }
             });
@@ -198,7 +198,7 @@ void scan_withNoDecoders_allowUnknown_returnsUnknownArray(String name) throws UR
                 for (Array column : chunk.columns().values()) {
                     assertThat(column).isInstanceOf(UnknownArray.class);
                     UnknownArray foreign = (UnknownArray) column;
-                    assertThat(foreign.encodingId()).describedAs(name).startsWith("vortex.");
+                    assertThat(foreign.encodingId().id()).describedAs(name).startsWith("vortex.");
                 }
             }
         }

reader/src/test/java/io/github/dfa1/vortex/reader/array/ArrayLimitedTest.java

@@ -1,6 +1,7 @@
 package io.github.dfa1.vortex.reader.array;
 
 import io.github.dfa1.vortex.core.model.DType;
+import io.github.dfa1.vortex.core.model.EncodingId;
 import io.github.dfa1.vortex.core.error.VortexException;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
@@ -321,7 +322,7 @@ class Unsupported {
         @Test
         void unknownArrayThrows() {
             // Given
-            UnknownArray sut = new UnknownArray("vortex.mystery", I64, 3, null,
+            UnknownArray sut = new UnknownArray(EncodingId.parse("vortex.mystery"), I64, 3, null,
                     new MemorySegment[0], new Array[0]);
 
             // When / Then

reader/src/test/java/io/github/dfa1/vortex/reader/array/ArrayMaterializeTest.java

@@ -1,6 +1,7 @@
 package io.github.dfa1.vortex.reader.array;
 
 import io.github.dfa1.vortex.core.model.DType;
+import io.github.dfa1.vortex.core.model.EncodingId;
 import io.github.dfa1.vortex.core.error.VortexException;
 import io.github.dfa1.vortex.core.io.PTypeIO;
 import org.junit.jupiter.api.Nested;
@@ -303,7 +304,7 @@ void bytePartsDecimalThrows() {
         @Test
         void unknownArrayThrows() {
             // Given an undecoded foreign encoding
-            UnknownArray sut = new UnknownArray("vortex.mystery", I64, 3, null,
+            UnknownArray sut = new UnknownArray(EncodingId.parse("vortex.mystery"), I64, 3, null,
                     new MemorySegment[0], new Array[0]);
 
             // When / Then