fix: MaterializedExecutor missing window/distinct + columnar edge cases

- MaterializedExecutor.execute() now applies window functions and distinct
  (previously silently dropped — any .window() or .distinct() on fromJSON/
  fromCSV DataFrames had no effect)
- Extract window evaluation into standalone applyWindowsToRows() for reuse
  (WindowOperator delegates to it; MaterializedExecutor calls it directly)
- columnar sliceColumnarBatch: clear nullBitmap on empty slice (stale ref)
- columnar kWayMerge: guard against missing sort column index (-1)

Author: teamchong

src/client.ts

@@ -15,8 +15,9 @@ import type {
   VectorSearchParams,
   WindowSpec,
 } from "./types.js";
-import { NULL_SENTINEL, rowComparator } from "./types.js";
+import { NULL_SENTINEL, rowComparator, groupKey } from "./types.js";
 import type { Operator, RowBatch } from "./operators.js";
+import { applyWindowsToRows } from "./operators.js";
 import { rowPassesFilters, bigIntReplacer } from "./decode.js";
 import { computePartialAgg, finalizePartialAgg } from "./partial-agg.js";
 import { descriptorToCode } from "./descriptor-to-code.js";
@@ -979,11 +980,27 @@ export class MaterializedExecutor implements QueryExecutor {
       });
     }
 
+    // Apply window functions (before filters, same order as operator pipeline)
+    if (query.windows && query.windows.length > 0) {
+      applyWindowsToRows(rows, query.windows);
+    }
+
     // Apply filters (AND + OR groups)
     if (query.filters.length > 0 || (query.filterGroups && query.filterGroups.length > 0)) {
       rows = rows.filter(row => rowPassesFilters(row, query.filters, query.filterGroups));
     }
 
+    // Apply distinct
+    if (query.distinct) {
+      const seen = new Set<string>();
+      rows = rows.filter(row => {
+        const key = groupKey(row, query.distinct!);
+        if (seen.has(key)) return false;
+        seen.add(key);
+        return true;
+      });
+    }
+
     // Apply aggregation
     if (query.aggregates && query.aggregates.length > 0) {
       const partial = computePartialAgg(rows, query);

src/columnar.ts

@@ -661,7 +661,7 @@ export function columnarKWayMerge(
   const indices: number[] = new Array(batches.length).fill(0);
   const heap: MergeHeapEntry[] = [];
   for (let i = 0; i < batches.length; i++) {
-    if (batches[i].rowCount > 0) {
+    if (batches[i].rowCount > 0 && sortColIndices[i] >= 0) {
       const sci = sortColIndices[i];
       heap.push({ batchIdx: i, rowIdx: 0, value: readColumnValue(batches[i].columns[sci], 0) });
       indices[i] = 1;
@@ -796,7 +796,7 @@ export function sliceColumnarBatch(batch: ColumnarBatch, offset: number, limit?:
   const start = Math.min(offset, batch.rowCount);
   const end = limit !== undefined ? Math.min(start + limit, batch.rowCount) : batch.rowCount;
   const rowCount = end - start;
-  if (rowCount <= 0) return { columns: batch.columns.map(c => ({ ...c, rowCount: 0, data: new ArrayBuffer(0) })), rowCount: 0 };
+  if (rowCount <= 0) return { columns: batch.columns.map(c => ({ ...c, rowCount: 0, data: new ArrayBuffer(0), nullBitmap: undefined })), rowCount: 0 };
   if (start === 0 && end === batch.rowCount) return batch;
 
   const columns: ColumnarColumn[] = [];