feat: plan 16 P1 (SEC-08/09/19/20/21) — fail-open/DoS/authz hardening

- SEC-08 pii-mask: fail-closed on missing rules / broken regex (no unmasked leak)
- SEC-09: input-size cap + fail-closed reads (security-check/drift-detect/context-compress); non-UTF8 no longer crashes
- SEC-19: control-plane store POSIX flock + atomic tmp+rename write
- SEC-20: new toolchain-verify.sh (missing/PATH-shadowed/in-workspace binary -> refuse); wired into harness-preflight
- SEC-21: model-call timeout 180->60s configurable + per-run call budget
- SEC-11 realized by SEC-17 prod profile (no code)
- 5 fail-able test suites wired into ci-harness-gate.sh; test-integrity manifest regenerated

Verify: SEC+integrity gate 16/0, run-casan4 0-FAIL, adversarial 44/44, no regressions.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

AINative_OKR_CASAN5/.specify/scripts/bash/security-check.sh

@@ -36,6 +36,15 @@ if [[ ! -f "$INPUT_FILE" ]]; then
   exit 1
 fi
 
+# SEC-09 (M-10): cap input size — the regex/normalize/decode passes are superlinear,
+# so an oversized input is a DoS vector. Fail CLOSED (block) rather than churn on it.
+CASAN_MAX_INPUT_BYTES="${CASAN_MAX_INPUT_BYTES:-2097152}"  # 2 MiB default
+INPUT_BYTES="$(wc -c < "$INPUT_FILE" 2>/dev/null | tr -d ' ')"
+if [[ -n "$INPUT_BYTES" && "$INPUT_BYTES" -gt "$CASAN_MAX_INPUT_BYTES" ]]; then
+  echo "SECURITY_BLOCKED: input exceeds cap ($INPUT_BYTES > $CASAN_MAX_INPUT_BYTES bytes)" >&2
+  exit 1
+fi
+
 timestamp() {
   date -u +"%Y-%m-%dT%H:%M:%SZ"
 }