feat: plan 16 P2 batch 1 (SEC-13 SSRF, SEC-27 log-escape, SEC-28 path-traversal)

- SEC-13 (M-09): SSRF allowlist on provider-usage-fetch (always block non-http(s)
  schemes; enforced mode blocks internal/link-local IPs + non-allowlisted hosts,
  dev keeps loopback mocks); dashboard refuses non-loopback bind in enforced mode.
- SEC-27 (X-02): casan-log strips ESC/CSI + CR/LF (terminal-escape + fake-log-line
  injection) while keeping tab and visible text.
- SEC-28 (X-04): new path-guard.sh — realpath resolve + reject symlink/.. escapes
  outside the allowed root.

Verify: SEC-13 6/0, SEC-27 3/0, SEC-28 4/0, adversarial 44/44, run-casan4 0-FAIL.

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

AINative_OKR_CASAN5/.specify/scripts/bash/path-guard.sh

@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+set -uo pipefail
+
+# CASAN Plan-16 SEC-28 (X-04) — path-traversal / symlink guard.
+#
+# A tool that takes a file path as input/output can be pointed at an arbitrary
+# location via `..` or a symlink (e.g. a symlink named "input.txt" -> /etc/passwd),
+# reading or writing outside the workspace. This resolves the REAL path (following
+# every symlink) and refuses anything that escapes the allowed root.
+#
+# Usage:  path-guard.sh <path> [allowed-root]     (default root: repo workspace)
+# Exit:   0 inside the root, 1 outside / unresolvable.
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_ROOT="$(cd "$SCRIPT_DIR/../../.." && pwd)"
+
+TARGET="${1:-}"
+ROOT="${2:-$PROJECT_ROOT}"
+if [[ -z "$TARGET" ]]; then
+  echo "Usage: path-guard.sh <path> [allowed-root]" >&2
+  exit 64
+fi
+
+python3 - "$TARGET" "$ROOT" <<'PY'
+import os
+import sys
+
+target, root = sys.argv[1], sys.argv[2]
+# realpath resolves symlinks in every existing path component and normalizes "..";
+# for a not-yet-created leaf it resolves the existing parent chain.
+real_target = os.path.realpath(target)
+real_root = os.path.realpath(root)
+
+if real_target == real_root or real_target.startswith(real_root + os.sep):
+    print(f"PATH_OK {real_target}")
+    sys.exit(0)
+sys.stderr.write(f"PATH_ESCAPES_ROOT target={target} real={real_target} root={real_root}\n")
+sys.exit(1)
+PY