fix(projects): preserve server picker recovery

src/main/java/com/lab/labtimesheet/feature/project/controller/ProjectController.java

@@ -164,8 +164,8 @@ public class ProjectController {
     }
 
     /**
-     * Adds all selected eligible Interns atomically or re-renders membership history with the
-     * complete retained selection and a safe validation message.
+     * Adds all selected eligible Interns atomically or re-renders membership history with every
+     * still-eligible selection retained and a count of unavailable choices.
      *
      * @param principal authenticated user
      * @param projectId owning Project identifier
@@ -182,16 +182,27 @@ public class ProjectController {
             BindingResult bindingResult,
             Model model) {
         long actorId = actorId(principal);
+        boolean rejectedByService = false;
         if (!bindingResult.hasErrors()) {
             try {
                 projects.addMembers(actorId, projectId, membersForm.internUserIds());
                 return "redirect:/projects/" + projectId + "/members";
             } catch (ProjectRuleViolationException exception) {
+                rejectedByService = true;
                 bindingResult.rejectValue(
                         "internUserIds", "project.members.ineligible", exception.getMessage());
             }
         }
-        populateMembersModel(actorId, projectId, model);
+        var refreshedOptions = populateMembersModel(actorId, projectId, model);
+        if (rejectedByService) {
+            Set<Long> refreshedIds = refreshedOptions.stream()
+                    .map(EligibleInternOption::userId)
+                    .collect(Collectors.toUnmodifiableSet());
+            long unavailableSelectionCount = membersForm.internUserIds().stream()
+                    .filter(userId -> !refreshedIds.contains(userId))
+                    .count();
+            model.addAttribute("unavailableSelectionCount", unavailableSelectionCount);
+        }
         return "projects/members";
     }
 
@@ -242,7 +253,7 @@ public class ProjectController {
         return "projects/leadership";
     }
 
-    private void populateMembersModel(long actorId, long projectId, Model model) {
+    private List<EligibleInternOption> populateMembersModel(long actorId, long projectId, Model model) {
         var project = pages.detail(actorId, projectId);
         var members = pages.members(actorId, projectId);
         model.addAttribute("project", project);
@@ -252,10 +263,13 @@ public class ProjectController {
                     .filter(member -> member.leftAt() == null)
                     .map(member -> member.internUserId())
                     .collect(Collectors.toUnmodifiableSet());
-            model.addAttribute("eligibleInternOptions", eligibleInternOptions().stream()
+            var options = eligibleInternOptions().stream()
                     .filter(option -> !currentMemberIds.contains(option.userId()))
-                    .toList());
+                    .toList();
+            model.addAttribute("eligibleInternOptions", options);
+            return options;
         }
+        return List.of();
     }
 
     private void populateLeadershipModel(long actorId, long projectId, Model model) {

src/main/resources/templates/projects/form.html

@@ -41,7 +41,7 @@
                         <input class="control" id="leader-search" type="search" autocomplete="off" data-picker-search>
                         <div class="picker-options">
                             <label class="picker-option" data-picker-option th:each="option : ${eligibleInternOptions}" th:attr="data-picker-search=${option.displayName + ' ' + option.studentCode}">
-                                <input type="radio" th:field="*{initialLeaderUserId}" th:value="${option.userId}" required>
+                                <input type="radio" th:field="*{initialLeaderUserId}" th:value="${option.userId}">
                                 <span><strong data-picker-label th:text="|${option.displayName} (${option.studentCode})|">Intern (Code)</strong><small th:text="|${#temporals.format(option.internshipStart, 'dd/MM/yyyy')} – ${#temporals.format(option.internshipEnd, 'dd/MM/yyyy')}|">Dates</small></span>
                             </label>
                             <p class="picker-empty" data-picker-empty th:hidden="${!#lists.isEmpty(eligibleInternOptions)}">No matching eligible Interns.</p>

src/main/resources/templates/projects/leadership.html

@@ -36,7 +36,7 @@
                     <input class="control" id="leadership-search" type="search" autocomplete="off" data-picker-search>
                     <div class="picker-options">
                         <label class="picker-option" data-picker-option th:each="option : ${eligibleInternOptions}" th:attr="data-picker-search=${option.displayName + ' ' + option.studentCode}">
-                            <input type="radio" th:field="*{internUserId}" th:value="${option.userId}" required>
+                            <input type="radio" th:field="*{internUserId}" th:value="${option.userId}">
                             <span><strong data-picker-label th:text="|${option.displayName} (${option.studentCode})|">Intern (Code)</strong><small th:text="|${#temporals.format(option.internshipStart, 'dd/MM/yyyy')} – ${#temporals.format(option.internshipEnd, 'dd/MM/yyyy')}|">Dates</small></span>
                         </label>
                         <p class="picker-empty" data-picker-empty th:hidden="${!#lists.isEmpty(eligibleInternOptions)}">No matching eligible current members.</p>

src/main/resources/templates/projects/members.html

@@ -29,6 +29,8 @@
             <p class="picker-summary" data-picker-summary aria-live="polite">No Interns selected</p>
             <p class="field-help" th:if="${#lists.isEmpty(eligibleInternOptions)}">No eligible nonmembers are available.</p>
             <p class="field-error" id="member-intern-user-error" role="alert" th:if="${#fields.hasErrors('internUserIds')}" th:errors="*{internUserIds}"></p>
+            <p class="field-help" role="status" th:if="${unavailableSelectionCount != null and unavailableSelectionCount > 0}"
+               th:text="${unavailableSelectionCount == 1 ? '1 previously selected Intern is no longer eligible; choose a replacement.' : unavailableSelectionCount + ' previously selected Interns are no longer eligible; choose replacements.'}">Unavailable selection recovery</p>
             <dialog class="picker-drawer" data-picker-dialog aria-labelledby="member-picker-title">
                 <div class="picker-header"><div><h2 class="panel-title" id="member-picker-title">Add Project members</h2><p class="field-help">Select one or more eligible Interns who are not current members.</p></div><button class="button" type="button" data-picker-cancel>Cancel</button></div>
                 <div class="picker-body">