Fix serverless update not saving new code with migration v2 (#15221)

## Context
Regression introduced in https://github.com/twentyhq/twenty/pull/15032
With the new code, we don't have access to the from/to from the
specialised builder anymore and we now rely on diffing result and cache
to create the action which broke serverless update because "code" is not
part of the cache nor part of the diffing (checksum is).
To maintain the existing architecture and keep it generic (by only
modifying the specialized builder), the serverless builder overrides the
parent validateAndBuild method

packages/twenty-server/src/engine/workspace-manager/workspace-migration-v2/workspace-migration-builder-v2/builders/serverless-function/workspace-migration-v2-serverless-function-actions-builder.service.ts

@@ -1,14 +1,17 @@
 import { Injectable } from '@nestjs/common';
 
 import { ALL_METADATA_NAME } from 'src/engine/metadata-modules/flat-entity/constant/all-metadata-name.constant';
-import { findFlatEntityByIdInFlatEntityMapsOrThrow } from 'src/engine/metadata-modules/flat-entity/utils/find-flat-entity-by-id-in-flat-entity-maps-or-throw.util';
+import { findFlatEntityByIdInFlatEntityMaps } from 'src/engine/metadata-modules/flat-entity/utils/find-flat-entity-by-id-in-flat-entity-maps.util';
 import { UpdateServerlessFunctionAction } from 'src/engine/workspace-manager/workspace-migration-v2/workspace-migration-builder-v2/builders/serverless-function/types/workspace-migration-serverless-function-action-v2.type';
-import { WorkspaceEntityMigrationBuilderV2Service } from 'src/engine/workspace-manager/workspace-migration-v2/workspace-migration-builder-v2/services/workspace-entity-migration-builder-v2.service';
+import {
+  ValidateAndBuildArgs,
+  ValidateAndBuildReturnType,
+  WorkspaceEntityMigrationBuilderV2Service,
+} from 'src/engine/workspace-manager/workspace-migration-v2/workspace-migration-builder-v2/services/workspace-entity-migration-builder-v2.service';
 import { FlatEntityUpdateValidationArgs } from 'src/engine/workspace-manager/workspace-migration-v2/workspace-migration-builder-v2/types/flat-entity-update-validation-args.type';
 import { FlatEntityValidationArgs } from 'src/engine/workspace-manager/workspace-migration-v2/workspace-migration-builder-v2/types/flat-entity-validation-args.type';
 import { FlatEntityValidationReturnType } from 'src/engine/workspace-manager/workspace-migration-v2/workspace-migration-builder-v2/types/flat-entity-validation-result.type';
 import { FlatServerlessFunctionValidatorService } from 'src/engine/workspace-manager/workspace-migration-v2/workspace-migration-builder-v2/validators/services/flat-serverless-function-validator.service';
-import { fromFlatEntityPropertiesUpdatesToPartialFlatEntity } from 'src/engine/workspace-manager/workspace-migration-v2/workspace-migration-runner-v2/utils/from-flat-entity-properties-updates-to-partial-flat-entity';
 
 @Injectable()
 export class WorkspaceMigrationV2ServerlessFunctionActionsBuilderService extends WorkspaceEntityMigrationBuilderV2Service<
@@ -20,6 +23,43 @@ export class WorkspaceMigrationV2ServerlessFunctionActionsBuilderService extends
     super(ALL_METADATA_NAME.serverlessFunction);
   }
 
+  public async validateAndBuild(
+    args: ValidateAndBuildArgs<typeof ALL_METADATA_NAME.serverlessFunction>,
+  ): Promise<
+    ValidateAndBuildReturnType<typeof ALL_METADATA_NAME.serverlessFunction>
+  > {
+    const { to: toFlatEntityMaps } = args;
+    const baseResult = await super.validateAndBuild(args);
+
+    if (baseResult.status === 'fail') {
+      return baseResult;
+    }
+
+    const updatedActions = baseResult.actions.updated.map((action) => {
+      if (action.type !== 'update_serverless_function') {
+        return action;
+      }
+
+      const toServerlessFunction = findFlatEntityByIdInFlatEntityMaps({
+        flatEntityId: action.serverlessFunctionId,
+        flatEntityMaps: toFlatEntityMaps,
+      });
+
+      return {
+        ...action,
+        code: toServerlessFunction?.code,
+      };
+    });
+
+    return {
+      ...baseResult,
+      actions: {
+        ...baseResult.actions,
+        updated: updatedActions,
+      },
+    };
+  }
+
   protected async validateFlatEntityCreation(
     args: FlatEntityValidationArgs<typeof ALL_METADATA_NAME.serverlessFunction>,
   ): Promise<
@@ -116,25 +156,12 @@ export class WorkspaceMigrationV2ServerlessFunctionActionsBuilderService extends
       dependencyOptimisticFlatEntityMaps,
       flatEntityId,
       flatEntityUpdates,
-      optimisticFlatEntityMaps,
     } = args;
 
-    const existingEntity = findFlatEntityByIdInFlatEntityMapsOrThrow({
-      flatEntityId,
-      flatEntityMaps: optimisticFlatEntityMaps,
-    });
-    const updatedEntity = {
-      ...existingEntity,
-      ...fromFlatEntityPropertiesUpdatesToPartialFlatEntity({
-        updates: flatEntityUpdates,
-      }),
-    };
-
     const updateServerlessFunctionAction: UpdateServerlessFunctionAction = {
       type: 'update_serverless_function',
       serverlessFunctionId: flatEntityId,
       updates: flatEntityUpdates,
-      code: updatedEntity.code,
     };
 
     return {