fix(apiserver): page tokens keep 63-bit job IDs exact (bug-1903 partial)

findPageTokenIndex decoded the token's unique_job_id into a float64;
array element IDs set bit 62, where float64 spacing is 1024, so paging
skipped rows or restarted at row 0 -- an endless loop for callers that
page until the token is empty (control/query of arrays over 1000
elements). Decode with UseNumber and keep integers as int64.

Found by the job-array-one-based-index feature validation.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/frontend/apiserver/store/query.go

@@ -2,6 +2,7 @@ package store
 
 import (
 	"apiserver/utils"
+	"bytes"
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
@@ -378,10 +379,23 @@ func findPageTokenIndex(rows []utils.OrderMap, pageToken string, orders []utils.
 	if err != nil {
 		return 0
 	}
+	// bug-1903: decode numbers exactly; a float64 cannot hold a 63-bit
+	// unique_job_id (array element IDs set bit 62).
 	var tokenData map[string]interface{}
-	if err := json.Unmarshal(jsonBytes, &tokenData); err != nil {
+	dec := json.NewDecoder(bytes.NewReader(jsonBytes))
+	dec.UseNumber()
+	if err := dec.Decode(&tokenData); err != nil {
 		return 0
 	}
+	for k, v := range tokenData {
+		if num, ok := v.(json.Number); ok {
+			if i, err := num.Int64(); err == nil {
+				tokenData[k] = i
+			} else if f, err := num.Float64(); err == nil {
+				tokenData[k] = f
+			}
+		}
+	}
 
 	for i, row := range rows {
 		match := true

src/frontend/apiserver/store/query_test.go

@@ -204,3 +204,42 @@ func TestExecuteQuery_Predicates_SetAfterBuildQueryOptions(t *testing.T) {
 		t.Fatalf("field selection after predicates: row = %v, want only job_id", got[0].Data)
 	}
 }
+
+// bug-1903: the page token carried unique_job_id through JSON into a
+// float64. Array element IDs set tag bit 62, where float64 spacing is
+// 1024, so the token no longer named the page's last row: pages skipped
+// rows or restarted at row 0 (an endless loop for callers that page until
+// the token is empty, e.g. control of a >1000-element array).
+func TestPaginateRowsArrayElementIDsRoundTripPageToken(t *testing.T) {
+	const n = 2500
+	base := int64(1)<<62 | int64(1700000000)<<20 | int64(32768)
+	rows := make([]utils.OrderMap, n)
+	for k := 1; k <= n; k++ {
+		rows[k-1] = utils.OrderMap{Data: map[string]interface{}{"unique_job_id": base + int64(k)}}
+	}
+	orders := []utils.SortOrder{{Column: "unique_job_id", Ascending: true}}
+
+	var got []int64
+	token := ""
+	for page := 0; ; page++ {
+		if page > 10 {
+			t.Fatalf("paging did not terminate after %d pages (%d rows seen)", page, len(got))
+		}
+		res, next := PaginateRows(rows, 1000, token, orders)
+		for _, r := range res {
+			got = append(got, r.Data["unique_job_id"].(int64)-base)
+		}
+		if next == "" {
+			break
+		}
+		token = next
+	}
+	if len(got) != n {
+		t.Fatalf("got %d rows, want %d", len(got), n)
+	}
+	for i, k := range got {
+		if k != int64(i+1) {
+			t.Fatalf("row %d is element %d, want %d", i, k, i+1)
+		}
+	}
+}