Multi-row `CREATE` followed by full-path `MERGE` causes a PostgreSQL backend segmentation fault

Docker image `apache/age:release_PG18_1.7.0`

**Reproduction**

```sql
LOAD 'age';
SET search_path = ag_catalog, public;
SELECT ag_catalog.create_graph('age_issue_case7');

SELECT *
FROM ag_catalog.cypher('age_issue_case7', $$
UNWIND [1331056905,1685130911] AS alias0
CREATE ({k0: true, k1: true, k3: false, k4: false, k5: 688047419, k11: 'Ad', k6: 'IZz', k10: -1671856916, k7: 't', k8: 644254522, k9: 'H2L3ye', id: 128, klist: [-693117962, 897437311, -1962790343]})
WITH alias0 AS alias1, [item IN range(12, 7, -1) WHERE item IS NOT NULL | toString(item)] AS alias2
WHERE ((('H0t' + 'KndeYYd') ENDS WITH 'ndeYYd') AND ((true AND true) AND true))
CREATE (n0:l0 {k1: true, k2: false, k3: false, id: 129, k6: 'Y', k7: 'C', k8: 1382373095, k9: 'Q', klist: [131362279, -1851970601, -1506840787, 2047568719]})
<-[r0:rt1 {k0: false, k1: false, k2: false, k3: true, k5: 1497504556, k11: 'ZCsD', id: 4, k10: 1255153251, k7: 'Y', k8: -900442765, k9: 'E', klist: []}]-
({k0: false, k2: false, k3: false, k4: false, k11: 'J', id: 130, k6: 'p', k10: -759664277, k7: 'V', k8: 129867760, k9: 'UsV8'})
WITH *
MERGE p0 = (n0) <-[r1:rt1 {k0: false, k1: true, k2: true, k3: false, k4: false, k5: 81415748, k11: 'B', k6: 'aYhBB0', k10: 1575911880, k7: 'F', k8: -2118834534, k9: 'yYD8Slu', id: 5, klist: [999780219]}]-
({k1: false, k2: false, k3: true, k4: false, k5: 1399012233, id: 131, k6: 'Q1wsEm', k10: 47426956, k8: -125428397, k9: 'r', klist: [-508132260, 1582656878]})
-[:rt8 {k0: true, k1: false, k2: true, k3: true, k4: false, k5: 586226905, k11: 'b', k6: 'z', k10: -760765339, k7: 'z', k8: 96686575, k9: 'x', id: 6, klist: [-1109084786]}]->
({k0: false, k1: true, k3: false, k4: false, k11: 'dTdqpT', id: 132, k10: -1589249357, k8: 390800412, klist: [172296092, 878100138, -1047680138]})
WITH alias2, r0.k9 AS alias3, round(toFloat(r0.k10)) AS alias4, n0 AS alias5, r0 AS alias6, r1 AS alias7, p0 AS alias8
WITH alias3 AS alias9, alias4, alias2 AS alias10, alias6.k11 AS alias11, alias5.k3 AS alias12, last(tail(nodes(alias8))) AS alias13, alias5 AS alias14, alias6 AS alias15, alias8
WITH *
CREATE (:l8 {k0: true, k1: false, k2: true, k3: true, k4: true, k5: -775427475, id: 133, k6: 'EkvHmp42', k10: -2013887244, k9: 'I', klist: [1515249301]})
RETURN alias14, alias15, alias8, alias11, alias13, alias4, alias12, atan(toFloat(alias14.id)) AS alias16, asin(toFloat(length(alias8))) AS alias17
ORDER BY alias11 DESC, alias4 DESC, alias12 ASC, alias16 ASC, alias17 ASC
LIMIT 15
$$) AS (c1 agtype, c2 agtype, c3 agtype, c4 agtype, c5 agtype,
c6 agtype, c7 agtype, c8 agtype, c9 agtype);
```

**Expected**

The valid query completes and leaves PostgreSQL available.

**Actual**

```text
server closed the connection unexpectedly
client backend ... was terminated by signal 11: Segmentation fault

Start by running the SQL reproduction against Docker image apache/age:release_PG18_1.7.0, using the documented CREATE and full-path MERGE query in this issue. Trace the PostgreSQL backend segmentation fault in the Apache AGE extension and add regression coverage for this query. Done means the valid query completes and PostgreSQL remains available without signal 11.

Written by the indexing model from the issue text.