Degrade chunkArray on unsealed sources to the general trait path

`array_chunk` with a constant length precisely enumerates the chunks
for sealed CATs: each chunk is a known slice of the source. With
real unsealed extras the source has an unknown number of trailing
entries that could form additional partial or full chunks — the
precise enumeration would lie about the chunk count.

Fall back to `traitChunkArray`, which yields the general
`non-empty-list<array{...source-shape...}>` form. Less precise but
correct.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ondrejmirtes

src/Type/Constant/ConstantArrayType.php

@@ -1436,6 +1436,15 @@ private static function isListAfterUnset(array $newKeyTypes, array $newOptionalK
 
 	public function chunkArray(Type $lengthType, TrinaryLogic $preserveKeys): Type
 	{
+		// With real unsealed extras, we can't precisely enumerate the
+		// chunks — the source has an unknown number of extras that
+		// could form additional partial or full chunks. Fall back to
+		// the general `list<chunk<sourceValues>>` shape produced by
+		// the trait, which is correct (just less precise).
+		if ($this->isUnsealed()->yes()) {
+			return $this->traitChunkArray($lengthType, $preserveKeys);
+		}
+
 		$biggerOne = IntegerRangeType::fromInterval(1, null);
 		$finiteTypes = $lengthType->getFiniteTypes();
 		if ($biggerOne->isSuperTypeOf($lengthType)->yes() && count($finiteTypes) < self::CHUNK_FINITE_TYPES_LIMIT) {

tests/PHPStan/Analyser/nsrt/unsealed-derivations.php

@@ -476,6 +476,26 @@ public function sliceBeyondExplicit(array $arr): void
 
 }
 
+class ChunkArray
+{
+
+	/**
+	 * @param array{a: 1, b: 2, c: 3, d: 4, ...<int, string>} $arr
+	 */
+	public function chunkPreservingKeys(array $arr): void
+	{
+		// With real unsealed extras the precise chunk count is unknown,
+		// so the type falls back to a general "non-empty list of chunks
+		// shaped like the source". Each chunk is described by the
+		// source's own shape (preserveKeys=true).
+		assertType(
+			'non-empty-list<array{a: 1, b: 2, c: 3, d: 4, ...<int, string>}>',
+			array_chunk($arr, 2, true),
+		);
+	}
+
+}
+
 class CountNarrowing
 {