gates: close the audit findings — enforce the gates the docs claimed

An adversarial audit found the enforcement story ahead of the code: gates
that were documented as hard gates were advisory, manual, or absent, and
several human-facing claims outran the machine record. This makes the
claims true.

High findings

- Differential fuzz was documentation, not enforcement: verdict hardcoded
  fuzz_iters=0 and diff-test hardcoded the gate to Skipped, while the case
  studies claimed 10k-iteration fuzz on the same wins. Fuzz is now a real
  pipeline gate (strict FUZZ-RESULT contract, executed count recorded), and
  it is inherently baseline-vs-candidate, so it runs on the accept path and
  reports Skipped in the standalone `just gates` flow. New hard rule: a
  machine `accepted` verdict is impossible unless the fuzz gate actually
  passed — otherwise it caps at needs-human-review.
- The agent's system prompt claimed FP/concurrency/unsafe patches were
  "routed to human review automatically". No such mechanism existed. Added
  a conservative lexical risk classifier (crates/verdict/src/risk.rs) that
  forces needs-human-review on any would-be accept carrying those signals;
  fp-tolerance equivalence always signals.
- The local verdict path ran agent-influenced code unsandboxed. It now runs
  under scripts/no-net.sh (network namespace) and fails closed. Upstream
  test suites are hash-verified against corpora/<t>/TESTSUITE.sha256 when
  present (scripts/pin-testsuite.sh generates them).

Also fixed, found while fixing the above

- The pipeline script's `set -e` was inert (brace group as the left operand
  of `&&`), so a failing candidate build did not abort the run and verdict
  could bench a stale binary. Now a scoped subshell whose status is branched
  on at top level.
- A wrapper that exits before exec'ing (no-net.sh refusing, bad wrapper path)
  stranded RUNNING.lock and left read_verdict polling forever. Failure
  accounting now lives outside the wrapper.
- harnessd's patch allowlist ignored git rename/copy headers and --no-prefix
  diffs; the rename-escape case is now a committed regression test.
- The workspace did not compile on Windows (ungated Unix APIs). cfg-gated;
  71 portable tests now run on both platforms.
- pin-check regenerated the corpus manifest instead of verifying it; it is
  now verify-only, with a deliberate `just pin-corpus` to re-pin.
- Max RSS is captured per run on Unix; PMU counters are opt-in diagnostics
  (compare --perf-stat), never part of the accept decision.

Docs now match the code, including what is NOT yet enforced: no target ships
a TESTSUITE.sha256 pin, no target declares [build].tsan, and matmul is not
wired to the fp-tolerance gate — each is stated as mechanized-but-inert
rather than done. Corrected the stale "33 ledger rows" (34), the playbook's
class-3 cJSON win (rejected), adversarial-review.md's sanitizer-separation
claim (five accepted rows carry sanitizers_clean=false), the unsupported
"40,000 requests" figure, and the blanket "historical rows record
fuzz_iters=0" (8 of 10; phase0-tokei-002/-003 record 4,332).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

corpora/cjson/gen-corpus.sh

@@ -4,8 +4,16 @@
 # with escapes and unicode, ints, floats (the strtod/sprintf hot path),
 # booleans, nulls. No randomness — byte-identical on every machine, so
 # the MANIFEST.sha256 pin is reproducible. Run from repo root:
-#   sh corpora/cjson/gen-corpus.sh
+#   sh corpora/cjson/gen-corpus.sh [--check|--pin]
+# Default/--check: regenerate and verify against MANIFEST.sha256 (never
+# rewrites it). --pin: deliberately rewrite the manifest.
 set -eu
+mode="check"
+case "${1:-}" in
+    "" | --check) ;;
+    --pin) mode="pin" ;;
+    *) echo "usage: gen-corpus.sh [--check|--pin]" >&2; exit 2 ;;
+esac
 DIR="$(cd "$(dirname "$0")" && pwd)"
 OUT="$DIR/input/big.json"
 mkdir -p "$DIR/input"
@@ -57,6 +65,14 @@ with open(sys.argv[1], "w") as f:
 PY
 
 echo "wrote $OUT ($(wc -c < "$OUT") bytes)"
-# Pin the corpus and regenerate the manifest.
-( cd "$DIR/input" && find . -type f -print0 | sort -z | xargs -0 sha256sum ) > "$DIR/MANIFEST.sha256"
-echo "manifest: $DIR/MANIFEST.sha256"
+if [ "$mode" = "pin" ]; then
+    ( cd "$DIR/input" && find . -type f -print0 | sort -z | xargs -0 sha256sum ) > "$DIR/MANIFEST.sha256"
+    echo "re-pinned $DIR/MANIFEST.sha256 — a deliberate human action (corpora/README.md);"
+    echo "commit the new manifest with justification."
+else
+    if [ ! -f "$DIR/MANIFEST.sha256" ]; then
+        echo "no MANIFEST.sha256 — pin the corpus with: sh corpora/cjson/gen-corpus.sh --pin" >&2
+        exit 1
+    fi
+    ( cd "$DIR/input" && sha256sum -c ../MANIFEST.sha256 )
+fi