fix: local-executor explain() used stale projections-only column set + missing filterGroups

explain() computed projectedColumns using only query.projections, not
including filter/sort/groupBy/aggregate/window/distinct/join columns.
This produced inaccurate estimatedBytes and estimatedR2Reads. Now uses
the same neededNames logic as the execute path.

Also adds filterGroups to the explain filters output (query-do already
had this) and fixes format.test.ts fixture that incorrectly showed IN
filter as non-pushable.

Author: teamchong

src/format.test.ts

@@ -126,7 +126,7 @@ describe("formatExplain", () => {
       fragments: 1,
       filters: [
         { column: "amount", op: "gt", pushable: true },
-        { column: "region", op: "in", pushable: false },
+        { column: "region", op: "in", pushable: true },
       ],
       metaCached: true,
     };
@@ -139,7 +139,7 @@ describe("formatExplain", () => {
     expect(output).toContain("name");
     expect(output).toContain("utf8");
     expect(output).toContain("amount gt  [pushable]");
-    expect(output).toContain("region in  [not pushable]");
+    expect(output).toContain("region in  [pushable]");
     expect(output).toContain("20 skipped (62.5%)");
     expect(output).toContain("128KB across 4 reads");
     expect(output).toContain("Meta: cached");

src/local-executor.ts

@@ -209,9 +209,22 @@ export class LocalExecutor implements QueryExecutor {
   async explain(query: QueryDescriptor): Promise<ExplainResult> {
     const meta = await this.getOrLoadMeta(query.table);
     const { columns } = meta;
-    const projectedColumns = query.projections.length > 0
-      ? columns.filter(c => query.projections.includes(c.name))
-      : columns;
+    const neededCols = new Set(query.projections.length > 0 ? query.projections : columns.map(c => c.name));
+    for (const f of query.filters) neededCols.add(f.column);
+    if (query.filterGroups) for (const g of query.filterGroups) for (const f of g) neededCols.add(f.column);
+    if (query.sortColumn) neededCols.add(query.sortColumn);
+    if (query.groupBy) for (const g of query.groupBy) neededCols.add(g);
+    if (query.aggregates) for (const a of query.aggregates) if (a.column !== "*") neededCols.add(a.column);
+    if (query.distinct) for (const d of query.distinct) neededCols.add(d);
+    if (query.windows) for (const w of query.windows) {
+      if (w.column) neededCols.add(w.column);
+      for (const p of w.partitionBy) neededCols.add(p);
+      for (const o of w.orderBy) neededCols.add(o.column);
+    }
+    if (query.join) neededCols.add(query.join.leftKey);
+    if (query.subqueryIn) for (const sq of query.subqueryIn) neededCols.add(sq.column);
+    if (query.vectorSearch) neededCols.add(query.vectorSearch.column);
+    const projectedColumns = columns.filter(c => neededCols.has(c.name));
 
     let pagesTotal = 0;
     let pagesSkipped = 0;
@@ -267,11 +280,10 @@ export class LocalExecutor implements QueryExecutor {
       fragments: this.datasetCache.get(query.table)?.fragmentMetas.size ?? 1,
       fragmentsScanned: this.datasetCache.get(query.table)?.fragmentMetas.size ?? 1,
       fanOut: false,
-      filters: query.filters.map(f => ({
-        column: f.column,
-        op: f.op,
-        pushable: true,
-      })),
+      filters: [
+        ...query.filters.map(f => ({ column: f.column, op: f.op, pushable: true })),
+        ...(query.filterGroups ?? []).flatMap(g => g.map(f => ({ column: f.column, op: f.op, pushable: true }))),
+      ],
       metaCached: this.metaCache.has(query.table),
     };
   }