feat(shares): add preview-validate endpoint, fix document attachment 500

ClerkShareWithdrawalRequestApiResource: extracted validate(Long)'s checklist
logic into buildShareWithdrawalChecks(Map<?, ?>) and added a new
POST /preview-validate endpoint that runs it against a draft submission (same
fields submit() accepts, same Sundry-downgrade rule applied first) instead of
an already-persisted request. Lets the clerk see the exact checklist a manager
will see on approval before the request is even submitted, with zero risk of
the two checklists drifting apart, since both now call the same method. The
one check validate() runs that a draft cannot -- "Maker and Checker are
different users" -- is reported as a fixed reminder instead of silently
dropped, since the clerk previewing this is necessarily the maker and no
checker has been chosen yet.

DocumentReadPlatformServiceImpl.retrieveDocumentContent(): a document/signature
whose m_document row survives but whose underlying file is missing from the
content store (the usual cause is a database copied between environments
without its file store) was throwing an uncaught ContentStoreException,
surfacing as a raw 500 on every fetch. Now caught and converted to the same
DocumentNotFoundException (404) ImageReadPlatformServiceImpl already uses for
the identical situation on client photos, so the frontend's existing
graceful-fallback handling for a missing attachment applies here too.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

fineract-document/src/main/java/org/apache/fineract/infrastructure/documentmanagement/service/DocumentReadPlatformServiceImpl.java

@@ -18,20 +18,29 @@
  */
 package org.apache.fineract.infrastructure.documentmanagement.service;
 
+import java.io.FileNotFoundException;
+import java.nio.file.NoSuchFileException;
 import java.util.List;
 import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
 import org.apache.fineract.infrastructure.contentstore.service.ContentStoreService;
+import org.apache.fineract.infrastructure.core.exception.AbstractPlatformDomainRuleException;
 import org.apache.fineract.infrastructure.documentmanagement.data.DocumentContent;
 import org.apache.fineract.infrastructure.documentmanagement.data.DocumentData;
 import org.apache.fineract.infrastructure.documentmanagement.domain.DocumentRepository;
+import org.apache.fineract.infrastructure.documentmanagement.exception.DocumentInvalidRequestException;
 import org.apache.fineract.infrastructure.documentmanagement.exception.DocumentNotFoundException;
 import org.apache.fineract.infrastructure.documentmanagement.mapping.DocumentMapper;
 import org.springframework.stereotype.Service;
 
+@Slf4j
 @Service
 @RequiredArgsConstructor
 public class DocumentReadPlatformServiceImpl implements DocumentReadPlatformService {
 
+    /** Bound on the cause walk below, so a self-referencing cause chain cannot spin. */
+    private static final int MAX_CAUSE_DEPTH = 10;
+
     private final ContentStoreService storeService;
     private final DocumentRepository documentRepository;
     private final DocumentMapper documentMapper;
@@ -52,9 +61,39 @@ public class DocumentReadPlatformServiceImpl implements DocumentReadPlatformServ
     public DocumentContent retrieveDocumentContent(final String entityType, final Long entityId, final Long documentId) {
         final var doc = documentRepository.findByIdAndParentEntityTypeAndParentEntityId(documentId, entityType, entityId)
                 .orElseThrow(() -> new DocumentNotFoundException(entityType, entityId, documentId));
-        final var is = storeService.download(doc.getLocation());
+        try {
+            final var is = storeService.download(doc.getLocation());
+            return documentMapper.map(doc, is);
+        } catch (final AbstractPlatformDomainRuleException e) {
+            throw e;
+        } catch (final Exception e) {
+            if (isMissingFromContentStore(e)) {
+                // The m_document row survives but the file it points at does not — the usual cause is
+                // a database copied between environments without its file store (see the identical
+                // guard in ImageReadPlatformServiceImpl). For the caller that is simply "this document
+                // has no content", not a server fault, so report it the same way as a missing document
+                // instead of letting a raw ContentStoreException surface as a 500.
+                log.warn("Document {} for {} {} is recorded but missing from the content store; treating it as not found", documentId,
+                        entityType, entityId);
+                throw new DocumentNotFoundException(entityType, entityId, documentId);
+            }
+            throw new DocumentInvalidRequestException(e);
+        }
+    }
 
-        return documentMapper.map(doc, is);
+    /**
+     * Whether a failure bottoms out in "the stored file is not there", however it was wrapped on the
+     * way up (the file store rethrows as ContentStoreException).
+     */
+    private boolean isMissingFromContentStore(final Throwable failure) {
+        Throwable cause = failure;
+        for (int depth = 0; cause != null && depth < MAX_CAUSE_DEPTH; depth++) {
+            if (cause instanceof NoSuchFileException || cause instanceof FileNotFoundException) {
+                return true;
+            }
+            cause = cause.getCause();
+        }
+        return false;
     }
 
     @Override