Port projections to pytest, all 75 names (#432)

CHANGELOG.md

@@ -18,6 +18,81 @@ true until the next version shipped.
 
 ### Added
 
+- `test/pytest/test_projections.py`: the multiple-projections DDL, catalog and read
+  path, ported from `test/projections.sh` (#432). All 75 of its check names, one for
+  one.
+
+  A projection is a second copy of some columns, and every property is about the copy
+  staying honest: it holds the rows the base holds, it loses the rows the base loses, it
+  survives a vacuum that renumbers every row underneath it, and the planner reads it only
+  when it can answer the whole query from it. A wrong projection is a WRONG ANSWER rather
+  than a slow one, because nothing downstream re-checks.
+
+  THE PORT IS STRICTLY STRONGER IN ONE PLACE, and it is worth saying which way. The
+  original's `expect_fail` helper runs the statement and passes when it errors AT ALL, so
+  a misspelt table name satisfies every one of its eight refusal arms. The port asserts
+  the SQLSTATE, and every code was measured against this build rather than guessed --
+  42710, 42703, 22023, 42701, 22023, 42809, 22023, 42704, 42704. The names are the bash
+  suite's; the assertions are not.
+
+  Three other mechanism changes assert the same property by a stronger means: the
+  `EXPLAIN` grep becomes a typed JSON field and reads the projection NAME rather than its
+  presence; `pgc_set_hash` becomes `expect.row_set`, order-blind by declaration rather
+  than by construction; and the second MVCC session becomes a second connection rather
+  than a background `psql` on a fifo polled for a token, which removes the wait rather
+  than shortening it.
+
+  Mutation proof, each asserting it applied before its result was believed: removing the
+  #875 projection-writer reset reddens both directions of the latch (`got 105 want 116`
+  on the mid-transaction add, and the orphan storage the mid-transaction drop leaves);
+  forcing the planner to refuse every projection reddens the covering query and the
+  post-vacuum planner arm with `got None want 'pc'`, which is what proves the port reads
+  the name rather than the presence. Restored, byte-identical: 75 checks, 0 fail.
+
+- `test/pytest/test_sorted_pathkeys.py`: the ordered-scan surface, ported from
+  `test/sorted_pathkeys.sh` (#432). All 110 of its check names, one for one.
+
+  The bash suite pins one decision: when a columnar scan may hand the planner
+  PATHKEYS, the promise that its rows already arrive in a stated order. The planner
+  then drops the Sort above the scan, and nothing downstream re-checks. So a wrong
+  promise is not a slow plan, it is WRONG ROWS.
+
+  The port keeps the original's three shapes rather than reorganising by feature: a
+  CLAIM arm (the Sort goes), a REFUSAL arm (something made the claim untrue and the
+  Sort comes back), and an ANSWER arm (the rows themselves, against a heap table
+  built from the same data). The ANSWER arm is not a duplicate of the CLAIM arm --
+  dropping the Sort is only correct if the rows arrive sorted anyway, and a plan
+  check alone cannot say whether they did.
+
+  THE ONE ARM THAT NEEDED MORE THAN A PORT is `pgcolumnar.parallel_copy`, which
+  prepares one transaction per worker. `max_prepared_transactions` cannot be raised
+  without restarting the postmaster, and the default is 0, so asking for fewer
+  workers does not help. `pgc_cluster` now sets it where it writes
+  `postgresql.conf`, at the value `lib.sh` gives this suite through
+  `PGC_EXTRA_CONF`. Refusing the arm instead was measured and rejected: it loses
+  three names outright (`cannot_run` records under the REASON CODE, #1040 phase 0b)
+  AND turns the `pytest (cluster tests)` job red, because an unrunnable check exits
+  67 and the job runs pytest under `set -euo pipefail`. That half exits 0 today with
+  zero unrun, so this file would have been the first to break it.
+
+- `test_docs_cover_the_corpus.py` now refuses a NUMBERED SECTION WITH NO BODY.
+
+  The arm above it asks whether each test file is NAMED by a numbered heading. A
+  heading with no body is still a heading, so a section inserted into the gap between
+  another heading and its body leaves both files named and one of them documented
+  under the wrong title -- every existing arm green. `## 37. test_iceberg_fdw.py`
+  reached `main` sitting directly above `## 38.`, with the Iceberg body attached to
+  the userinfo heading. Fixed here, and the section order now matches the bodies.
+
+### Fixed
+
+- `compare_to_bash.py`'s corpus arm called a WRAPPED name fabricated. A name too long
+  for one line is written as adjacent literals, and Python joins them at parse time,
+  so the joined name is text the file contains but not text `in src` can find. The
+  arm exists to catch a reader that CONSTRUCTS a name, so it now collapses the file's
+  own concatenation and keeps exactly that guarantee: an f-string name still yields a
+  `{}` template, which the collapse does not rescue. Both directions are asserted.
+
 - `orphan-scan` is armed in the matrix runner, so a ledger row naming a deleted
   check is refused rather than reported (#983, #1015).