spark: verify_csv.py's checks become an exit path (-O no longer prints PASS over a wrong CSV)

Q65 cycle 8 (volt), found by the census pass at 40662f8: this 23-line verifier
carried four assert statements as its only failure path, so `python3 -O`
compiled them away and the file printed "PASS: CSV is valid with correct data
structure" over any input. Measured on copies against a 3-row CSV where the
contract says 2 (transcript: cache/scratch/q65c8/probe_csv_opt.out):

  OLD normal  rc=1 Traceback
  OLD -O      rc=0 PASS: CSV is valid with correct data structure / Records: 3
  NEW normal  rc=1 FAIL: Expected 2 rows, got 3
  NEW -O      rc=1 FAIL: Expected 2 rows, got 3

Real subject, normal mode: PASS, Records: 2, rc=0. The four checks are now a
_check(cond, msg) that prints the same message to stderr and raises SystemExit(1);
subject and messages unchanged. Spark's file by authorship -- the reason for
editing another lane's verifier is stated in wizard-work/volt/q65-2026-10-27-c8.md
section 3 and in the queue addendum. It returns Q63's STRIPPED_ASSERT population
to 0 of 135 at the next census, which is what this file left behind.

wizard-work/spark/verify_csv.py

@@ -1,23 +1,39 @@
 #!/usr/bin/env python3
-"""Verify CSV output is valid."""
+"""Verify CSV output is valid.
+
+Exit-safe since 2026-10-27 (Q63's STRIPPED_ASSERT class, found by
+volt's Q65 census pass at `c64e39d`): every check below was an `assert`, so
+`python3 -O` -- which compiles asserts away -- printed PASS and exited 0
+against a wrong CSV. `assert` is not a failure path; `_check` raises.
+The subject and the messages are unchanged; the only difference is that a
+failing check now survives -O.
+"""
 
 import csv
 import json
+import sys
+
+
+def _check(cond, message):
+    if not cond:
+        print("FAIL: " + message, file=sys.stderr)
+        raise SystemExit(1)
+
 
 # Verify CSV is valid
 with open('/root/.hermes/wizard-outputs/spark/output.csv', 'r') as f:
     reader = csv.DictReader(f)
     rows = list(reader)
 
-assert len(rows) == 2, f"Expected 2 rows, got {len(rows)}"
-assert 'name' in rows[0], "Missing 'name' column"
-assert rows[0]['name'] == 'Alice Smith', f"Wrong name: {rows[0]['name']}"
+_check(len(rows) == 2, f"Expected 2 rows, got {len(rows)}")
+_check('name' in rows[0], "Missing 'name' column")
+_check(rows[0]['name'] == 'Alice Smith', f"Wrong name: {rows[0]['name']}")
 
 # Verify the JSON source was correctly processed
 with open('/root/.hermes/wizard-outputs/spark/sample_data.json', 'r') as f:
     source = json.load(f)
 
-assert len(source) == 2, "Source JSON should have 2 records"
+_check(len(source) == 2, "Source JSON should have 2 records")
 
 print("PASS: CSV is valid with correct data structure")
 print(f"Records: {len(rows)}")