feat: Add Lisp Validator skill with 3-phase deterministic gate

- Implements structural (O(n) paren balance), syntactic (reader with *read-eval* nil),
  and semantic (whitelist AST walk) validation.
- Exposes :validate-lisp cognitive tool for Probabilistic Engine self-correction.
- Replaces validate-lisp-syntax stub in harness/skills.org with delegation.
- Adds mandatory validation rule to Probabilistic Engine system prompt.
- Refactors org-skill-policy.org with 6 concrete invariants (Transparency, Autonomy,
  Zero-Bloat, Modularity, Mentorship, Sustainability) and explicit override hierarchy.
- Adds Harness Boundary Contract to harness/manifest.org.

tests/lisp-validator-tests.lisp

@@ -0,0 +1,70 @@
+(defpackage :opencortex-lisp-validator-tests
+  (:use :cl :fiveam :opencortex)
+  (:export #:lisp-validator-suite))
+
+(in-package :opencortex-lisp-validator-tests)
+
+(def-suite lisp-validator-suite
+  :description "Tests for the Lisp Validator structural, syntactic, and semantic gates.")
+
+(in-suite lisp-validator-suite)
+
+(test structural-balanced
+  (let ((result (opencortex::lisp-validator-check-structural "(+ 1 2)")))
+    (is (eq result t))))
+
+(test structural-unbalanced-open
+  (multiple-value-bind (ok reason line col)
+      (opencortex::lisp-validator-check-structural "(+ 1 2")
+    (is (null ok))
+    (is (search "Unbalanced" reason))
+    (is (= line 1))))
+
+(test structural-unbalanced-close
+  (multiple-value-bind (ok reason line col)
+      (opencortex::lisp-validator-check-structural "+ 1 2)")
+    (is (null ok))
+    (is (search "Unexpected" reason)))
+
+(test structural-mismatched-bracket
+  (multiple-value-bind (ok reason line col)
+      (opencortex::lisp-validator-check-structural "(let [x 1) x)")
+    (is (null ok))
+    (is (search "Mismatched" reason))))
+
+(test syntactic-valid
+  (multiple-value-bind (ok reason line col)
+      (opencortex::lisp-validator-check-syntactic "(+ 1 2) (* 3 4)")
+    (is ok)))
+
+(test syntactic-invalid-reader
+  (multiple-value-bind (ok reason line col)
+      (opencortex::lisp-validator-check-syntactic "(1+ 2 #")")
+    (is (null ok))))
+
+(test semantic-safe
+  (multiple-value-bind (ok reason line col)
+      (opencortex::lisp-validator-check-semantic "(+ 1 2)")
+    (is ok)))
+
+(test semantic-blocked-eval
+  (multiple-value-bind (ok reason line col)
+      (opencortex::lisp-validator-check-semantic "(eval '(+ 1 2))")
+    (is (null ok))))
+
+(test unified-success
+  (let ((result (opencortex::lisp-validator-validate "(+ 1 2)" :strict t)))
+    (is (eq (getf result :status) :success))
+    (is (getf (getf result :checks) :structural))
+    (is (getf (getf result :checks) :syntactic))
+    (is (getf (getf result :checks) :semantic))))
+
+(test unified-structural-failure
+  (let ((result (opencortex::lisp-validator-validate "(+ 1 2" :strict nil)))
+    (is (eq (getf result :status) :error))
+    (is (eq (getf result :failed) :structural))))
+
+(test unified-semantic-failure-strict
+  (let ((result (opencortex::lisp-validator-validate "(delete-file \"x.txt\")" :strict t)))
+    (is (eq (getf result :status) :error))
+    (is (eq (getf result :failed) :semantic))))