fix: propagate compound state through toAst() and canonical lowering

ast.ts: Add optional compoundOperator and compoundParts fields to
  RelationAssertion, allowing compound fluent assertions to carry
  their .and / .or structure through the AST layer.

fluent.ts: toAst() now emits compoundOperator/compoundParts when
  isCompound, closing the gap where compound state was silently
  dropped in canonical extraction, preset building, and validation.

lower-to-canonical.ts: Handle RelationAssertion with compound metadata
  by lowering each part as a separate grouped clause (same groupId,
  same compoundOperator), matching DSL parser compound behavior.

validator.ts: Validate options on each compound part, closing the
  false-positive validation gap where only the final relation was checked.

3 lossy code paths (extractCanonicalFromAssertion, presets.toPresetResult,
validateRelation) now preserve compound structure. Primary FOL evaluation
path was already correct (fol-compiler reads compoundParts directly).

658 tests pass.

packages/imhotep-dsl/src/validator.ts

@@ -262,6 +262,28 @@ export function validateRelation(assertion: RelationAssertion): ValidationResult
     )
   }
 
+  // 6. Compound parts: validate each part's relation name and options
+  if (assertion.compoundOperator && assertion.compoundParts && assertion.compoundParts.length > 1) {
+    for (let i = 0; i < assertion.compoundParts.length; i++) {
+      const part = assertion.compoundParts[i]
+      const partAllowed = getValidOptionsForRelation(part.relation)
+      const partOpts = part.options as unknown as Record<string, unknown>
+      const partProvided = Object.keys(partOpts).filter(k => k !== 'type')
+      for (const key of partProvided) {
+        if (!partAllowed.has(key)) {
+          diagnostics.push(
+            makeDiag(
+              'IMH_VALID_ILLEGAL_RELATION_OPTION',
+              'validation-error',
+              `Option "${key}" is not valid for compound part "${part.relation}". Allowed options: ${Array.from(partAllowed).join(', ') || 'none'}.`,
+              assertion.position,
+            ),
+          )
+        }
+      }
+    }
+  }
+
   return {
     valid: diagnostics.length === 0,
     diagnostics,