fix: preserve nested loop body flow traversal

mdl-examples/bug-tests/328-describer-nested-loop-body-flows.mdl

@@ -0,0 +1,66 @@
+-- ============================================================================
+-- Bug #328: DESCRIBE MICROFLOW omitted nested loop body continuation flows
+-- ============================================================================
+--
+-- Symptom (before fix):
+--   Some microflow graphs store the loop boundary flow (last body activity →
+--   loop iterator) in the loop's local object collection, while the real
+--   body-to-body continuation flows are stored in the parent microflow
+--   graph. When a body activity already had a local outgoing flow (the
+--   boundary one), the describer ignored parent-level flows with the same
+--   origin. Result: activities downstream of that origin disappeared from
+--   the described loop body — most visible on nested loops, where the
+--   inner body collapsed into one statement.
+--
+-- Root cause:
+--   `emitLoopBody` built a fresh `loopFlowsByOrigin` from the loop's local
+--   object collection only, then short-circuited when an origin had a
+--   local entry, never merging the equivalent parent-level flows.
+--
+-- After fix:
+--   The describer now merges parent-level body flows into the loop-local
+--   traversal map for any origin that lives in the loop body, including
+--   nested loop descendants collected recursively.
+--
+-- Usage:
+--   mxcli exec mdl-examples/bug-tests/328-describer-nested-loop-body-flows.mdl -p app.mpr
+--   mxcli -p app.mpr -c "describe microflow BugTest328.MF_NestedLoops"
+--   The describe output must contain BOTH outer- and inner-loop body
+--   activities and must be a fixpoint under describe → exec → describe.
+-- ============================================================================
+
+create module BugTest328;
+
+create entity BugTest328.Item (
+  Name : string(100)
+);
+/
+
+create entity BugTest328.Role (
+  Name : string(100)
+);
+/
+
+create microflow BugTest328.MF_NestedLoops (
+  $Items: list of BugTest328.Item,
+  $Roles: list of BugTest328.Role
+)
+begin
+  log info node 'BugTest328' 'before outer';
+
+  loop $Item in $Items
+  begin
+    log info node 'BugTest328' 'outer head';
+
+    loop $Role in $Roles
+    begin
+      log info node 'BugTest328' 'inner body';
+      log info node 'BugTest328' 'inner tail';
+    end loop;
+
+    log info node 'BugTest328' 'outer tail';
+  end loop;
+
+  log info node 'BugTest328' 'after outer';
+end;
+/

mdl/executor/cmd_microflows_builder.go

@@ -53,7 +53,7 @@ type flowBuilder struct {
 	microflowsCacheLoaded bool
 	nanoflowsCache        []*microflows.Nanoflow
 	nanoflowsCacheLoaded  bool
-	manualLoopBackTarget model.ID
+	manualLoopBackTarget  model.ID
 }
 
 // addError records a validation error during flow building.

mdl/executor/cmd_microflows_format_action.go

@@ -351,30 +351,30 @@ func formatAction(
 
 			stmt := fmt.Sprintf("retrieve $%s from %s", outputVar, entityName)
 
-		if dbSource.XPathConstraint != "" {
-			constraint := strings.TrimSpace(dbSource.XPathConstraint)
-			// XPath may contain multiple predicates like [a][b] or [a]\n[b].
-			// Split them and join with MDL 'and' so the parser sees
-			// separate xpathConstraint nodes.
-			if strings.HasPrefix(constraint, "[") && strings.HasSuffix(constraint, "]") {
-				// Split on "][" boundary (possibly separated by \n literals),
-				// then re-wrap each predicate.
-				inner := constraint[1 : len(constraint)-1]
-				// Normalise real newlines between predicates: ]\n[ → ][
-				inner = strings.ReplaceAll(inner, "]\n[", "][")
-				parts := strings.Split(inner, "][")
-				if len(parts) > 1 {
-					var wrapped []string
-					for _, p := range parts {
-						wrapped = append(wrapped, "["+strings.TrimSpace(p)+"]")
+			if dbSource.XPathConstraint != "" {
+				constraint := strings.TrimSpace(dbSource.XPathConstraint)
+				// XPath may contain multiple predicates like [a][b] or [a]\n[b].
+				// Split them and join with MDL 'and' so the parser sees
+				// separate xpathConstraint nodes.
+				if strings.HasPrefix(constraint, "[") && strings.HasSuffix(constraint, "]") {
+					// Split on "][" boundary (possibly separated by \n literals),
+					// then re-wrap each predicate.
+					inner := constraint[1 : len(constraint)-1]
+					// Normalise real newlines between predicates: ]\n[ → ][
+					inner = strings.ReplaceAll(inner, "]\n[", "][")
+					parts := strings.Split(inner, "][")
+					if len(parts) > 1 {
+						var wrapped []string
+						for _, p := range parts {
+							wrapped = append(wrapped, "["+strings.TrimSpace(p)+"]")
+						}
+						constraint = strings.Join(wrapped, "\n    ")
+					} else {
+						constraint = parts[0]
 					}
-					constraint = strings.Join(wrapped, "\n    ")
-				} else {
-					constraint = parts[0]
 				}
+				stmt += fmt.Sprintf("\n    where %s", constraint)
 			}
-			stmt += fmt.Sprintf("\n    where %s", constraint)
-		}
 
 			// Output SORT BY clause if present
 			if len(dbSource.Sorting) > 0 {

mdl/executor/cmd_microflows_show.go

@@ -844,16 +844,25 @@ func findSplitMergePoints(
 	oc *microflows.MicroflowObjectCollection,
 	activityMap map[model.ID]microflows.MicroflowObject,
 ) map[model.ID]model.ID {
-	result := make(map[model.ID]model.ID)
-
 	// Build flow graph for forward traversal
 	flowsByOrigin := make(map[model.ID][]*microflows.SequenceFlow)
 	for _, flow := range oc.Flows {
 		flowsByOrigin[flow.OriginID] = append(flowsByOrigin[flow.OriginID], flow)
 	}
 
-	// For each ExclusiveSplit, find its merge point
-	for _, obj := range oc.Objects {
+	return findSplitMergePointsForGraph(ctx, activityMap, flowsByOrigin)
+}
+
+// findSplitMergePointsForGraph finds the corresponding merge point for each
+// split in an already materialized flow graph. Nested traversals such as loop
+// bodies use this because they do not have a top-level object collection.
+func findSplitMergePointsForGraph(
+	ctx *ExecContext,
+	activityMap map[model.ID]microflows.MicroflowObject,
+	flowsByOrigin map[model.ID][]*microflows.SequenceFlow,
+) map[model.ID]model.ID {
+	result := make(map[model.ID]model.ID)
+	for _, obj := range activityMap {
 		if _, ok := obj.(*microflows.ExclusiveSplit); ok {
 			splitID := obj.GetID()
 			// Find merge by following both branches until they converge