fix: deterministic code-point string collation for column store + aggregation

Replace localeCompare (default-locale, non-deterministic across environments —
unsafe for a persisted sorted index) with UTF-8 byte / code-point order via a
shared compareCodePoints() helper. String ordering is now deterministic and
byte-identical to the native column store / aggregation sort, so results are the
same with or without the native accelerator. Covers the aggregate orderBy sort
and all 5 column-store comparison sites (tail buffer, merge sort, binary search).
Adds compareCodePoints unit tests.

src/indexes/columnStore/ColumnSegmentCursor.ts

@@ -14,6 +14,7 @@
 import type { SegmentHeader } from './types.js'
 import { ValueType } from './types.js'
 import type { RoaringBitmap32 } from '../../utils/roaring/index.js'
+import { compareCodePoints } from '../../utils/collation.js'
 
 /**
  * Binary search result.
@@ -100,7 +101,7 @@ export class ColumnSegmentCursor {
     while (lo < hi) {
       const mid = (lo + hi) >>> 1
       const cmp = isString
-        ? String(this.values[mid]).localeCompare(String(target))
+        ? compareCodePoints(String(this.values[mid]), String(target))
         : (this.values[mid] as number) - (target as number)
 
       if (cmp < 0) {
@@ -136,7 +137,7 @@ export class ColumnSegmentCursor {
     while (endLo < endHi) {
       const mid = (endLo + endHi) >>> 1
       const cmp = isString
-        ? String(this.values[mid]).localeCompare(String(hi))
+        ? compareCodePoints(String(this.values[mid]), String(hi))
         : (this.values[mid] as number) - (hi as number)
       if (cmp <= 0) {
         endLo = mid + 1

src/indexes/columnStore/ColumnStore.ts

@@ -30,6 +30,7 @@ import { ColumnManifest } from './ColumnManifest.js'
 import { ColumnSegmentCursor, TailBufferCursor, type CursorEntry } from './ColumnSegmentCursor.js'
 import { writeSegmentToBuffer, readSegmentFromBuffer } from './ColumnSegmentFormat.js'
 import { RoaringBitmap32 } from '../../utils/roaring/index.js'
+import { compareCodePoints } from '../../utils/collation.js'
 
 /**
  * Configuration for the ColumnStore.
@@ -554,7 +555,7 @@ export class ColumnStore implements ColumnStoreProvider {
     // Sort a copy for the cursor
     const sorted = entries.slice().sort((a, b) => {
       if (valueType === ValueType.String) {
-        return String(a.value).localeCompare(String(b.value))
+        return compareCodePoints(String(a.value), String(b.value))
       }
       return (a.value as number) - (b.value as number)
     })
@@ -615,7 +616,7 @@ export class ColumnStore implements ColumnStoreProvider {
     const compare = (a: HeapEntry, b: HeapEntry): number => {
       let cmp: number
       if (isString) {
-        cmp = String(a.value).localeCompare(String(b.value))
+        cmp = compareCodePoints(String(a.value), String(b.value))
       } else {
         cmp = (a.value as number) - (b.value as number)
       }

src/indexes/columnStore/ColumnTailBuffer.ts

@@ -12,6 +12,7 @@
  */
 
 import { ValueType, DEFAULT_FLUSH_THRESHOLD } from './types.js'
+import { compareCodePoints } from '../../utils/collation.js'
 
 /**
  * Entry in the tail buffer: a (value, entityIntId) pair.
@@ -131,7 +132,7 @@ export class ColumnTailBuffer {
     const sorted = this.entries.slice()
     if (this.valueType === ValueType.String) {
       sorted.sort((a, b) => {
-        const cmp = String(a.value).localeCompare(String(b.value))
+        const cmp = compareCodePoints(String(a.value), String(b.value))
         return cmp !== 0 ? cmp : a.entityIntId - b.entityIntId
       })
     } else {