test: native_chunk_length_bound's fetch check is an arm, and names its own failure (#1339)

test/check_ledger.tsv

@@ -2279,7 +2279,7 @@ native_chunk_length_bound	native_chunk_length_bound	an index fetch of a chunk wh
 native_chunk_length_bound	native_chunk_length_bound	backend survived the sequential refusal	15;16;17;18;19	never	-
 native_chunk_length_bound	native_chunk_length_bound	backend survived the truncated-length fetch	15;16;17;18;19	never	-
 native_chunk_length_bound	native_chunk_length_bound	premise: a point lookup uses the index, not a sequential columnar scan	15;16;17;18;19	never	-
-native_chunk_length_bound	native_chunk_length_bound	premise: that fetch returns the row	15;16;17;18;19	never	-
+native_chunk_length_bound	native_chunk_length_bound	that fetch returns the row	15;16;17;18;19	2026-10-16	the index fetch treated a flushed row as not live, so the lookup returned no row (mutation, #1339)
 native_delete_visibility_paths	native_delete_visibility_paths	a DELETE whose qual deletes another row of the table succeeds and leaves heap's rows (#1394)	15;16;17;18;19	2026-10-14	PgColumnarUpsertDeleteVector without the command advance (main before #1394's fix)
 native_delete_visibility_paths	native_delete_visibility_paths	a deleted row is invisible via the index	15;16;17;18;19	never	-
 native_delete_visibility_paths	native_delete_visibility_paths	a live row is visible via the index	15;16;17;18;19	never	-

test/check_ledger_budget.txt

@@ -2933,4 +2933,14 @@ suites_not_covered 219
 #     never         2678 - 2 = 2676
 #     dated          941 + 2 = 943
 #     2676 + 943 == 3619
-checks_never_observed_red 2676
+#
+# #1339, native_chunk_length_bound's "that fetch returns the row" was a premise a
+# product change reddens (jdatcmd): 2676 -> 2675. It becomes an arm, its row renamed
+# with its history, dated by the index fetch treating a flushed row as not live. The
+# plan premise beside it stays a premise. No row is added or removed.
+#
+#     ledger rows   3619 + 0 = 3619
+#     never         2676 - 1 = 2675
+#     dated          943 + 1 = 944
+#     2675 + 944 == 3619
+checks_never_observed_red 2675

test/native_chunk_length_bound.sh

@@ -49,7 +49,10 @@ fetch_val() {
 	env PATH="$PGC_BINDIR:$PATH" psql -h 127.0.0.1 -p "$PGC_PORT" -U postgres -d "$PGC_DB" \
 		-Atq -c "$1" 2>&1 | grep -v '^SET$' | tail -1
 }
-check "premise: that fetch returns the row" \
+# An arm, not a premise (#1339, #1236): an index fetch that treats a flushed row as
+# not live returns no row here. The plan premise above stays a premise: with the
+# scans off, the planner, not this repository, chooses the index.
+check "that fetch returns the row" \
 	"$(fetch_val "${FETCH} SELECT t FROM clb WHERE id = 1;")" "v1"
 
 q "UPDATE pgcolumnar.column_chunk SET page_length = page_length + 4294967296

test/pytest/test_native_chunk_length_bound.py

@@ -53,8 +53,14 @@ def test_native_chunk_length_bound(pgc_conn, expect):
         cur.execute("SET enable_bitmapscan=off")
         cur.execute("SET pgcolumnar.enable_custom_scan=off")
         cur.execute("SELECT t FROM clb WHERE id = 1")
-        got = cur.fetchone()[0]
-    expect.text(got, "v1", "premise: that fetch returns the row")
+        # A missing row is this check's failure, by name (#1339): fetchone()[0] on
+        # no row raised TypeError, and the run never said which check it was.
+        row = cur.fetchone()
+        got = row[0] if row else "<no row>"
+    # An arm, not a premise (#1339, #1236): an index fetch that treats a flushed row
+    # as not live returns no row here. The plan premise above stays a premise: with
+    # the scans off, the planner, not this repository, chooses the index.
+    expect.text(got, "v1", "that fetch returns the row")
 
     with pgc_conn.cursor() as cur:
         cur.execute(