feat(260728-lih): make LDAP sync strictly selective (empty selection = no-op)

- collectSearchEntries() returns [] on empty/undefined groupFilterDns
  instead of scanning the whole baseDn subtree
- syncUsersForTenant() early-returns an empty successful result before
  any LDAP search or the deactivation loop when groupFilterDns is empty,
  so an empty selection can never mass-deactivate existing LDAP users
- Updated exclude-list tests to use a non-empty groupFilterDns; added a
  dedicated no-op test proving empty selection performs zero search/
  create/update/deactivate operations

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/api/src/ldap/ldap.service.spec.ts

@@ -34,7 +34,10 @@ describe('LdapService.syncUsersForTenant — per-user exclude list', () => {
     serverUrl: 'ldap://example',
     baseDn: 'dc=example,dc=com',
     searchFilter: '(objectClass=person)',
-    groupFilterDns: [] as string[],
+    // Non-empty selection: an empty groupFilterDns is now a no-op (see the
+    // dedicated "empty selection no-op" describe block below), so these
+    // exclude-list tests need a real selection to exercise the search path.
+    groupFilterDns: ['ou=people,dc=example,dc=com'] as string[],
     userExcludeList: [] as string[],
     fieldMappings: [
       { ldapField: 'sAMAccountName', tesseraField: 'username' },
@@ -115,6 +118,55 @@ describe('LdapService.syncUsersForTenant — per-user exclude list', () => {
   });
 });
 
+describe('LdapService.syncUsersForTenant — empty selection no-op', () => {
+  let service: LdapService;
+  let prisma: any;
+  let userService: any;
+
+  const emptySelectionConfig = {
+    id: 'cfg1',
+    tenantId: 't1',
+    serverUrl: 'ldap://example',
+    baseDn: 'dc=example,dc=com',
+    searchFilter: '(objectClass=person)',
+    groupFilterDns: [] as string[],
+    userExcludeList: [] as string[],
+    fieldMappings: [
+      { ldapField: 'sAMAccountName', tesseraField: 'username' },
+    ],
+  };
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockBind.mockResolvedValue(undefined);
+    mockUnbind.mockResolvedValue(undefined);
+    prisma = {
+      user: {
+        findFirst: vi.fn().mockResolvedValue(null),
+        findMany: vi.fn().mockResolvedValue([{ id: 'u-existing', ldapDn: 'cn=existing' }]),
+        update: vi.fn().mockResolvedValue({}),
+      },
+      ldapConfig: { update: vi.fn().mockResolvedValue({}) },
+    };
+    userService = { create: vi.fn().mockResolvedValue({}) };
+    service = new LdapService(prisma, userService);
+  });
+
+  it('creates nobody and deactivates nobody when groupFilterDns is empty', async () => {
+    const result = await service.syncUsersForTenant(
+      emptySelectionConfig as any,
+      't1',
+    );
+
+    expect(result).toEqual({ created: 0, updated: 0, deactivated: 0, errors: [] });
+    expect(mockSearch).not.toHaveBeenCalled();
+    expect(mockBind).not.toHaveBeenCalled();
+    expect(userService.create).not.toHaveBeenCalled();
+    expect(prisma.user.update).not.toHaveBeenCalled();
+    expect(prisma.ldapConfig.update).not.toHaveBeenCalled();
+  });
+});
+
 describe('LdapService — individual user search & import (dedup)', () => {
   let service: LdapService;
   let prisma: any;

apps/api/src/ldap/ldap.service.ts

@@ -534,6 +534,17 @@ export class LdapService {
       errors: [],
     };
 
+    // DELIBERATE back-compat break + critical safety guard: an empty/undefined
+    // groupFilterDns now means "sync nothing", not "import everyone under
+    // baseDn". Returning here BEFORE any LDAP search and BEFORE the
+    // deactivation loop below is what prevents an empty selection from
+    // mass-deactivating every existing LDAP user (there would be no synced
+    // DNs to compare against, so every local LDAP user would look "removed").
+    // lastSyncAt is intentionally left untouched on this no-op path.
+    if (!config.groupFilterDns || config.groupFilterDns.length === 0) {
+      return result;
+    }
+
     const client = new Client(
       this.buildClientOptions(config.serverUrl, config.tlsRejectUnauthorized),
     );
@@ -673,8 +684,11 @@ export class LdapService {
    * Run the directory search for syncUsersForTenant, applying the selective
    * group/OU import filter (groupFilterDns) when one is configured.
    *
-   * - Empty groupFilterDns: single search of baseDn with sanitizedFilter
-   *   (identical to pre-filter behavior, backward compatible).
+   * - Empty groupFilterDns: DELIBERATE no-op — returns [] without ever
+   *   searching the directory. A selective sync now means "nothing selected
+   *   = nothing synced", not "import everyone under baseDn" (back-compat
+   *   break, see syncUsersForTenant's early-return guard which normally
+   *   short-circuits before this method is even reached).
    * - Non-empty groupFilterDns: split into OU DNs (used as extra search
    *   bases) and group DNs (matched via memberOf on the base search).
    *   Results are merged and deduped by entry dn.
@@ -686,12 +700,7 @@ export class LdapService {
     attributes: string[],
   ) {
     if (!config.groupFilterDns || config.groupFilterDns.length === 0) {
-      const { searchEntries } = await client.search(config.baseDn, {
-        filter: sanitizedFilter,
-        attributes,
-        scope: 'sub',
-      });
-      return searchEntries;
+      return [];
     }
 
     const ouBases = config.groupFilterDns.filter((dn) => /^ou=/i.test(dn));