feat: cross-language Q&A (Operation Sandwich) + Windows quickstart — all default-OFF

Three workstreams, full suite 2482 passed, experimental paths default-OFF.

#000055 — Windows quickstart without make
  tasks.py (pure-stdlib runner) + make.bat shim + .gitattributes;
  README Windows section rewritten. Quickstart needs only Python
  3.10+ (no make/bzip2/curl/bash). Mirrors the Makefile quickstart
  subset; drift-pinned by tests/test_tasks_runner.py.

#000001 §7 Phase 0 — deterministic cross-language guard
  arborist/qa/crosslang.py: non-English signal (¿/¡/non-ASCII) + an
  es function-word stoppack. Fail-closed to UNGROUNDED before
  retrieval/LLM (mirrors the quantifier reject-DAG) when no content
  token survives, else strips es stopwords from the retrieval query
  only. English path byte-identical by construction. Default OFF
  (crosslang_guard_enabled). Measured: the anarcocapitalismo field
  case 10.4s -> 1.6s.

#000056 — Operation Sandwich (cross-language grounding)
  arborist/qa/mt/: opus-mt es/fr/ru<->en, lazy per-pair memoised
  singleton (fixes the 88%-engine-error concurrency defect),
  manifest-pinned, [mt] extra; entity_mask wrapper. Sandwich =
  translate query in (retrieval + LLM prompt) -> English answer ->
  UNTOUCHED verifier grounds English-vs-English -> translate the
  verified answer out as display-only (banner-labelled, zero
  grounding). question_hash + verifier_policy_hash invariant; MT
  engine identity binds into RetrievalPlan, not governance. CLI
  --crosslang-translate / make XLANG_MT=1. Default OFF; entity_mask
  default OFF (measured net-negative at bench scale). Fan-out bench
  (bench/*.py): Spanish ~0% -> 71% grounded vs the real no-support
  baseline; the round-trip predictor was tried and refuted; the
  entity-mask lever failed at scale (corpus-title anchoring untried).

CLAUDE.md: cross-language bright-line convention + module map.
Pre-existing modified diagram files are intentionally excluded.

bench/es_join_patterns.py

@@ -0,0 +1,61 @@
+#!/usr/bin/env python3
+"""Join the live es+sandwich sweep against the deterministic round-trip
+buckets → does MT round-trip drift PREDICT grounding loss?
+
+  sweep JSONL (question=es, audit_mode, status)
+     ⋈ es_roundtrip.json (es → bucket CLEAN/DRIFT/COLLAPSE)
+  → crosstab bucket × audit_mode, plus the MT-engine error rate
+    (the concurrency defect the fan-out surfaced) reported separately
+    so it doesn't get conflated with the MT-quality signal.
+"""
+from __future__ import annotations
+
+import json
+import sys
+from collections import Counter, defaultdict
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+RES = ROOT / "bench" / "qa_results"
+
+
+def main() -> int:
+    sweep_path = Path(sys.argv[1]) if len(sys.argv) > 1 else max(
+        RES.glob("2026-*.jsonl"), key=lambda p: p.stat().st_mtime)
+    rt = {r["es"]: r for r in json.loads((RES / "es_roundtrip.json").read_text())}
+    rows = [json.loads(ln) for ln in sweep_path.read_text().splitlines() if ln.strip()]
+
+    err = [r for r in rows if (r.get("status") or "").startswith(("err", "error"))
+           or r.get("audit_mode") is None]
+    ok = [r for r in rows if r not in err]
+    print(f"sweep: {sweep_path.name}  rows={len(rows)}  "
+          f"engine/other ERROR={len(err)} ({len(err)/max(1,len(rows)):.0%})  "
+          f"scored={len(ok)}")
+
+    ct = defaultdict(Counter)
+    unmatched = 0
+    for r in ok:
+        b = rt.get(r["question"], {}).get("bucket")
+        if b is None:
+            unmatched += 1
+            continue
+        ct[b][r.get("audit_mode") or "?"] += 1
+    print("\nbucket × audit_mode (scored rows only):")
+    modes = ["STRICT", "HYBRID", "UNGROUNDED", "?"]
+    print(f"  {'bucket':<9} " + " ".join(f"{m:>10}" for m in modes) + "   ground%")
+    for b in ("CLEAN", "DRIFT", "COLLAPSE"):
+        c = ct.get(b, Counter())
+        tot = sum(c.values())
+        g = c["STRICT"] + c["HYBRID"]
+        print(f"  {b:<9} " + " ".join(f"{c[m]:>10}" for m in modes)
+              + f"   {g}/{tot}" + (f" ({g/tot:.0%})" if tot else ""))
+    if unmatched:
+        print(f"  ({unmatched} scored rows had no round-trip match)")
+    print("\nreading: if CLEAN grounds >> COLLAPSE, MT round-trip drift "
+          "predicts grounding loss — the lever is entity-preserving MT, "
+          "not the sandwich architecture.")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())