Refactor phase handling in training unit sections for improved data integrity

- Introduced canonicalization for plan locations in phased saves to ensure consistent phase representation.
- Enhanced the `inheritPlanLocForPhasedSave` function to utilize the new canonicalization logic, improving data flow.
- Updated payload building logic to check for canonicalized plan locations, ensuring accurate phase detection during saves.

frontend/src/utils/trainingUnitSectionsForm.js

@@ -721,20 +721,47 @@ function stripPlanLoc(sec) {
   return rest
 }
 
-export function inheritPlanLocForPhasedSave(sections) {
-  let prev = {
-    phaseKind: 'whole_group',
-    phaseOrderIndex: 0,
-    parallelStreamOrderIndex: null,
-    phaseTitle: null,
-    phaseGuidanceNotes: null,
-    streamTitle: null,
-    streamNotes: null,
-    streamAssignedTrainerProfileIds: null,
+function phaseIndexToInt(v, fallback = 0) {
+  if (v === null || v === undefined || v === '') return fallback
+  const n = typeof v === 'number' ? v : Number(v)
+  return Number.isFinite(n) ? n : fallback
+}
+
+/**
+ * planLoc für Phasen-PUT kanonisieren (Großschreibung, numerische Indizes).
+ * Verhindert u. a. abgebrochene Phasen-Runs bei "0" !== 0 und falsche whole_group-Zweige.
+ */
+function canonicalPlanLocForPhasedSave(pl) {
+  if (!pl || typeof pl !== 'object') return null
+  const rawKind = String(pl.phaseKind || '').toLowerCase().trim()
+  let kind = rawKind === 'parallel' || rawKind === 'whole_group' ? rawKind : null
+  if (
+    !kind &&
+    pl.parallelStreamOrderIndex != null &&
+    pl.parallelStreamOrderIndex !== ''
+  ) {
+    kind = 'parallel'
   }
+  if (!kind) return null
+  const phaseOrderIndex = phaseIndexToInt(pl.phaseOrderIndex, 0)
+  let parallelStreamOrderIndex = null
+  if (kind === 'parallel') {
+    parallelStreamOrderIndex = phaseIndexToInt(pl.parallelStreamOrderIndex, 0)
+  }
+  return {
+    ...pl,
+    phaseKind: kind,
+    phaseOrderIndex,
+    parallelStreamOrderIndex,
+  }
+}
+
+export function inheritPlanLocForPhasedSave(sections) {
+  let prev = { ...defaultPlanLocWholeGroup(0) }
   return (sections || []).map((s) => {
-    if (s?.planLoc && s.planLoc.phaseKind) {
-      prev = { ...s.planLoc }
+    const canon = canonicalPlanLocForPhasedSave(s?.planLoc)
+    if (canon) {
+      prev = { ...canon }
       return { ...s, planLoc: prev }
     }
     return { ...s, planLoc: { ...prev } }
@@ -1127,7 +1154,7 @@ function buildPhasesPayloadFromFlat(sections) {
  */
 export function buildPlanPayloadForSave(sections) {
   const list = Array.isArray(sections) ? sections : []
-  const anyPhased = list.some((s) => s && s.planLoc && s.planLoc.phaseKind)
+  const anyPhased = list.some((s) => s && canonicalPlanLocForPhasedSave(s.planLoc) != null)
   if (!anyPhased) {
     return { sections: buildSectionsPayload(list) }
   }