bench(harnessx-removal): deterministic baseline without the extra (task 1)

Equality script (design section 3) records suite outcomes, `ousast pairs --json`,
the python-vulnerable quick benchmark, one standard scan and `improve --dry-run`
from a frozen export with the harnessx extra absent and no model reachable.
Two independent records are byte-identical (determinism.json).

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

benchmarks/measurements/2026-09-30-harnessx-removal-baseline/determinism.json

@@ -0,0 +1,16 @@
+{
+ "baseline": "this directory (record run A)",
+ "candidate": "record run B: second independent record from a fresh export of the same tree, same venv; not committed",
+ "differences": [],
+ "equal": true,
+ "exclusions": [
+  "JSON keys: created_at, finished, generated_at, runtime_seconds, scan_id, started, timestamp",
+  "JSON keys ending in: _seconds, _ms",
+  "run directory names / run ids (<timestamp>-<8 hex>, benchmark.py create_benchmark_run, run.py create_scan_run) -> <RUN_ID>",
+  "trace/events.jsonl as a whole (timings); never copied",
+  "the export's absolute root path -> <ROOT>; the children's TMPDIR -> <TMP>",
+  "suite: only the outcome per test id is kept (junit durations dropped)",
+  "env.json is a provenance record (commit, freeze hash, instrument checks), not compared"
+ ],
+ "raw_bytes_identical": "all 15 files incl. env.json (diff -r empty)"
+}