initial commit: @arbiter/core authorization engine with js-rigor hardening

Zanzibar-style authorization graph engine (direct/chain/TTU/defeasible/
binary modes, condensed snapshots, value relations) with 39 rigor test
campaigns. Includes fixes for snapshot binary writer/reader format
mismatch (snapshot-of-snapshot corruption), possibility write-boundary
validation, empty-graph snapshot serialization, relation lookup cache
direction collision, config-redefinition cache invalidation, binary
threshold semantics, defeasible compiled routing, and comparator
reason whitelisting.

src/ast/nodes/EvidenceBodyNode.js

@@ -0,0 +1,82 @@
+import { BaseNode } from './BaseNode.js';
+
+/**
+ * AST node for evidence body containing statements
+ * Represents: { statement1; statement2; ... }
+ */
+export class EvidenceBodyNode extends BaseNode {
+  constructor(location = null) {
+    super('EvidenceBody', location);
+    this.statements = [];
+  }
+
+  /**
+   * Add a statement to the evidence body
+   * @param {BaseNode} statement - Statement to add
+   */
+  addStatement(statement) {
+    this.statements.push(statement);
+    this.addChild(statement);
+  }
+
+  /**
+   * Get all statements of a specific type
+   * @param {string} type - Statement type to filter by
+   * @returns {BaseNode[]} Filtered statements
+   */
+  getStatementsOfType(type) {
+    return this.statements.filter(stmt => stmt.type === type);
+  }
+
+  /**
+   * Get all direct evidence statements
+   * @returns {DirectEvidenceNode[]} Direct evidence statements
+   */
+  getDirectEvidence() {
+    return this.getStatementsOfType('DirectEvidence');
+  }
+
+  /**
+   * Get all pattern matching statements
+   * @returns {PatternMatchNode[]} Pattern matching statements
+   */
+  getPatternMatches() {
+    return this.getStatementsOfType('PatternMatch');
+  }
+
+  /**
+   * Get all defeasible logic statements
+   * @returns {DefeasibleLogicNode[]} Defeasible logic statements
+   */
+  getDefeasibleLogic() {
+    return this.getStatementsOfType('DefeasibleLogic');
+  }
+
+  /**
+   * Get all fusion statements
+   * @returns {FusionNode[]} Fusion statements
+   */
+  getFusions() {
+    return this.getStatementsOfType('Fusion');
+  }
+
+  /**
+   * Validate the evidence body
+   * @returns {string[]} Array of error messages
+   */
+  validate() {
+    const errors = [];
+
+    // Validate each statement
+    this.statements.forEach((stmt, index) => {
+      const stmtErrors = stmt.validate ? stmt.validate() : [];
+      errors.push(...stmtErrors.map(err => `Statement ${index + 1}: ${err}`));
+    });
+
+    return errors;
+  }
+
+  toString() {
+    return `EvidenceBody(${this.statements.length} statements)`;
+  }
+}