pgsql: Track RI fast-path FK-check batches per firing cycle

Track RI fast-path FK-check batches per firing cycle

Commit 34a30786293 fixed an RI fast-path crash under nested C-level SPI
by keeping batch-callback lists per after-trigger query depth. That fix
was incomplete: the RI fast path still tracked callback registration
with one global flag. Once an outer firing cycle had registered its
callback, the flag suppressed registration for a nested cycle, leaving
the nested batch to be handled by the outer callback, too late and with
the wrong snapshot, potentially after the ResourceOwner holding its
relations had gone away.

Nor is per-depth callback registration sufficient while the cache is
keyed only by constraint OID. If nested firing checks the same
constraint, it reuses the outer entry, combining rows that must be
checked in separate firing cycles.

Key the cache by both constraint OID and query depth. Register a callback
for each depth that creates an entry, and make ri_FastPathEndBatch() flush
and release only entries belonging to the ending depth. Add
AfterTriggerCurrentQueryDepth() so ri_triggers.c can obtain the current
depth; depth -1 represents deferred firing.

Add regression coverage for nested firing through a cursor portal, whose
resources must not outlive the nested cycle, nested firing of the same
constraint at different query depths, and deferred firing at query depth
-1.

Reported-by: Noah Misch <noah(at)leadboat(dot)com>
Reported-by: Peter Geoghegan <pg(at)bowt(dot)ie>
Discussion: https://postgr.es/m/20260705222115.be.noahmisch@microsoft.com
Discussion: https://postgr.es/m/CAH2-Wz=D533JbF_ak_Pc8kP0FKse-ju8DnMxtjvY==yHsP4xgw@mail.gmail.com
Backpatch-through: 19

Branch
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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/d2a710c7e9e08e101694fe6c1f6789f18f9d3dcf

Modified Files
--------------
src/backend/commands/trigger.c | 14 ++++
src/backend/utils/adt/ri_triggers.c | 106 +++++++++++++++++++++++-------
src/include/commands/trigger.h | 1 +
src/test/regress/expected/foreign_key.out | 92 ++++++++++++++++++++++++++
src/test/regress/sql/foreign_key.sql | 78 ++++++++++++++++++++++
src/tools/pgindent/typedefs.list | 1 +
6 files changed, 269 insertions(+), 23 deletions(-)