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>

justfile

@@ -23,10 +23,15 @@ compare baseline candidate:
     cargo run -p bench-runner -- --config config/accept.toml compare \
         --baseline "{{baseline}}" --candidate "{{candidate}}"
 
-# Verify a target corpus against its pinned manifest
-# (wired through diff-test CLI once it exists; manual check for now)
+# Verify a target corpus against its pinned manifest (never rewrites it)
 pin-check target:
-    cd corpora/{{target}} && sh gen-corpus.sh
+    cd corpora/{{target}} && sh gen-corpus.sh --check
+
+# Deliberately re-pin a target corpus manifest — a trust-layer change;
+# review and commit the new MANIFEST.sha256 with justification
+pin-corpus target:
+    @echo "WARNING: rewriting corpora/{{target}}/MANIFEST.sha256 — deliberate human action (corpora/README.md)"
+    cd corpora/{{target}} && sh gen-corpus.sh --pin
 
 # Automated calibration: N A/A sessions (<5% false-positive required) +
 # N injected-slowdown sessions (>=95% detection required), JSON evidence
@@ -34,8 +39,10 @@ calibrate cmd out sessions="20":
     cargo run -p bench-runner -- --config config/accept.toml calibrate \
         --cmd "{{cmd}}" --sessions {{sessions}} --out "{{out}}"
 
-# Equivalence gates for a target: corpus pin (refuses on mismatch) ->
-# upstream tests -> golden replay. Fuzz/sanitizers stay per-attempt.
+# Equivalence gates for a target: corpus + test-suite pins (refuse on
+# mismatch) -> upstream tests -> golden replay. Differential fuzz needs a
+# pristine baseline to differ against, so it reports Skipped here and runs
+# for real on the accept path; sanitizers likewise run in verdict.
 gates target:
     cargo run -p diff-test -- {{target}}