feat(track-c-mvp): C3 data-exfil guard + C6 sandbox scaffold + Phase 2 suite

C3 (V19) data-exfil-guard.sh: destination-aware egress checkpoint built on the
  H4 detectors. cloud/artifact boundaries fail closed on any secret; audit
  boundary emits a PII-masked copy (fail closed on an unmaskable secret).
  Covers secret-to-cloud, artifact-leaks-env, and PII-in-audit.
C6 (V22) sandbox-run.sh: static policy pre-check (BLOCK on reading ~/.ssh/creds,
  network egress, fork bomb, writes outside workspace, huge-file/disk-fill) plus
  ulimit file-size/CPU backstops and the wall-clock timeout. HONEST SCOPE: this
  is not kernel isolation — the production target (docker --network=none
  --read-only --pids-limit / nsjail) is documented as TODO(C6-prod). Process cap
  is opt-in so it never breaks legitimate commands on a busy host.
phase2-track-c-tests.sh: 29 adversarial checks (C1 13, C2 6, C3 4, C6 6).
  Baselines preserved: run-casan4 35/35, adversarial 44/44.
  Running total: 35 + 44 + 25 + 29 = 133 checks.

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

AINative_OKR_CASAN5/.specify/scripts/bash/data-exfil-guard.sh

@@ -0,0 +1,80 @@
+#!/usr/bin/env bash
+set -uo pipefail
+
+# CASAN Track C-MVP — Data-exfiltration guard (C3, V19).
+#
+# Content leaving the trusted boundary must not carry secrets/PII. This guard
+# is the checkpoint for three egress destinations, each with its own policy:
+#
+#   cloud    — content about to be sent to a CLOUD model (OpenAI/Anthropic).
+#              A secret => BLOCK (fail closed); PII => masked copy emitted.
+#              Critical once Plan-03 wires a real cloud backend.
+#   audit    — content about to be written to an audit/log record.
+#              PII/secret => masked copy emitted (BLOCK if masking impossible).
+#   artifact — a generated artifact about to be persisted/shared.
+#              Any secret / env-token => BLOCK.
+#
+# It reuses security-check.sh's secret/PII detection + masking (single source of
+# truth) and applies the destination policy on top. Deterministic; no model call.
+#
+# Usage: data-exfil-guard.sh <file> <cloud|audit|artifact> [masked-output-file]
+# Exit: 0 allowed (possibly masked), 2 blocked (secret at a fail-closed boundary),
+#       64 usage.
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+# shellcheck source=casan-log.sh
+source "$SCRIPT_DIR/casan-log.sh"
+
+FILE="${1:-}"
+DEST="${2:-}"
+MASKED_OUT="${3:-}"
+
+if [[ -z "$FILE" || ! -f "$FILE" || -z "$DEST" ]]; then
+  echo "Usage: data-exfil-guard.sh <file> <cloud|audit|artifact> [masked-output-file]" >&2
+  exit 64
+fi
+case "$DEST" in cloud|audit|artifact) ;; *) echo "unknown destination: $DEST" >&2; exit 64 ;; esac
+
+SCAN_OUT="$(mktemp)"
+trap 'rm -f "$SCAN_OUT"' EXIT
+
+# Deterministic detection: security-check input-mode (semantic OFF). rc==2 means
+# a secret/critical pattern was found; on rc==0 SCAN_OUT holds the PII-masked copy.
+CASAN_SECURITY_STRICT=0 CASAN_SEMANTIC_CLASSIFY=0 \
+  bash "$SCRIPT_DIR/security-check.sh" "$FILE" "$SCAN_OUT" input >/dev/null 2>&1
+SC_RC=$?
+
+if [[ "$SC_RC" -eq 2 ]]; then
+  # A secret / private key / connection string / card was detected.
+  case "$DEST" in
+    cloud)
+      casan_log error data-exfil "DATA_EXFIL_BLOCKED destination=cloud reason=secret_would_leave_org"
+      echo "DATA_EXFIL_BLOCKED destination=cloud reason=secret_in_content" >&2
+      exit 2 ;;
+    artifact)
+      casan_log error data-exfil "DATA_EXFIL_BLOCKED destination=artifact reason=secret_or_env_token"
+      echo "DATA_EXFIL_BLOCKED destination=artifact reason=secret_or_env_token" >&2
+      exit 2 ;;
+    audit)
+      # Audit must never store a raw secret and must never lose the record; if we
+      # cannot safely mask a hard secret we fail closed rather than log it raw.
+      casan_log error data-exfil "DATA_EXFIL_BLOCKED destination=audit reason=unmaskable_secret"
+      echo "DATA_EXFIL_BLOCKED destination=audit reason=unmaskable_secret" >&2
+      exit 2 ;;
+  esac
+elif [[ "$SC_RC" -ne 0 ]]; then
+  echo "DATA_EXFIL_SCAN_ERROR destination=$DEST rc=$SC_RC" >&2
+  exit 2  # fail closed on scan error
+fi
+
+# rc==0: content is safe; SCAN_OUT is the PII-masked copy.
+if [[ -n "$MASKED_OUT" ]]; then
+  cp "$SCAN_OUT" "$MASKED_OUT"
+fi
+if ! cmp -s "$FILE" "$SCAN_OUT"; then
+  casan_log info data-exfil "DATA_EXFIL_MASKED destination=$DEST (PII redacted before egress)"
+  echo "DATA_EXFIL_MASKED destination=$DEST"
+else
+  echo "DATA_EXFIL_CLEAN destination=$DEST"
+fi
+exit 0