SQL Server - How do I Create/COMMIT Log Records during a Running Process that will potentially be ROLLEDBACK - sql-server

Question

I am having much difficulty attempting to replicate Logging as I had done in Oracle using PRAGRMA AUTOMOUS_TRANSACTION which allows you to COMMIT records to a LOG table while NOT COMMITing any other DML operations. I've been banging my head as to how more experienced SQL Server guys are LOGGING the Success or Errors of their Database Programs/Processes. Bascially how are experienced T-SQL guys logging in the middle of an active T-SQL program? Another way to put it... I have a HUGE process that is NOT to be COMMITed until the entire process executes without Critical Errors but I still need to log ALL Errors and if it's a Critical Error then ROLLBACK entire process but I still need the Logs.
Using MERGE as Example demonstrating my inability to COMMIT some records but ROLLING back others ...
I have TWO named Transactions in the below script (1. sourceData, 2. mainProcess)... This is my first attempt at trying to accomplish this goal. First the script INSERTs records using the 1st Transaction into a table without COMMIT. Then in Transaction 2 in the MERGE block I am INSERTing records into the Destination table and the Log table and I COMMIT transaction 2 (mainProcess).
I then AM ROLLING BACK the 1st named Transaction (sourceData)..
The issue is... EVERYTHING is getting ROLLED Back even though I explicitly COMMITed the mainProcess Transaction.
GO
/* temp table to simulate Log Table */
IF OBJECT_ID('tempdb..#LogTable') IS NULL
CREATE TABLE #LogTable
( Action VARCHAR(50),
primaryID INT,
secondaryID INT,
CustomID INT,
Note VARCHAR(200),
ConvDate DATE
) --DROP TABLE IF EXISTS #LogTable;
; /* SELECT * FROM #LogTable; TRUNCATE TABLE #LogTable; */
/* SELECT * FROM #ProductionSrcTable */
IF OBJECT_ID('tempdb..#ProductionSrcTable') IS NULL
CREATE TABLE #ProductionSrcTable( primaryKey INT, contactName VARCHAR(200), sourceKey INT )
; --DROP TABLE IF EXISTS #ProductionSrcTable; TRUNCATE TABLE #ProductionSrcTable;
/* SELECT * FROM #ProductionDestTable */
IF OBJECT_ID('tempdb..#ProductionDestTable') IS NULL
CREATE TABLE #ProductionDestTable( primaryKey INT, contactName VARCHAR(200), secondaryKey INT )
; --DROP TABLE IF EXISTS #ProductionDestTable; TRUNCATE TABLE #ProductionDestTable;
GO
/* Insert some fake data into Source Table */
BEGIN TRAN sourceData
BEGIN TRY
INSERT INTO #ProductionSrcTable
SELECT 1001 AS primaryKey, 'Jason' AS contactName, 789105 AS sourceKey UNION ALL
SELECT 1002 AS primaryKey, 'Jane' AS contactName, 789185 AS sourceKey UNION ALL
SELECT 1003 AS primaryKey, 'Sam' AS contactName, 788181 AS sourceKey UNION ALL
SELECT 1004 AS primaryKey, 'Susan' AS contactName, 681181 AS sourceKey
;
END TRY
BEGIN CATCH
ROLLBACK TRANSACTION sourceData
END CATCH
/* COMMIT below is purposely commented out in order to Test */
--COMMIT TRANSACTION sourceData
GO
BEGIN TRAN mainProcess
DECLARE #insertedRecords INT = 0,
#CustomID INT = 2,
#Note VARCHAR(200) = 'Test Temp DB Record Population via OUTPUT Clause',
#ConvDate DATE = getDate()
;
BEGIN TRY
MERGE INTO #ProductionDestTable AS dest
USING
(
SELECT src.primaryKey, src.contactName, src.sourceKey FROM #ProductionSrcTable src
) AS src ON src.primaryKey = dest.primaryKey AND src.sourceKey = dest.secondaryKey
WHEN NOT MATCHED BY TARGET
THEN
INSERT --INTO ProductionDestTable
( primaryKey, contactName, secondaryKey )
VALUES
( src.primaryKey, src.contactName, src.sourceKey )
/* Insert Output in Log Table */
OUTPUT $action, inserted.primaryKey, src.sourceKey, #CustomID, #Note, #ConvDate INTO #LogTable;
; /* END MERGE */
/* Store the number of inserted Records into the insertedRecords variable */
SET #insertedRecords = ##ROWCOUNT;
END TRY
BEGIN CATCH
ROLLBACK TRANSACTION mainProcess
END CATCH
;
--ROLLBACK TRANSACTION mainProcess
COMMIT TRANSACTION mainProcess
ROLLBACK TRANSACTION sourceData
PRINT 'Records Inserted:' + CAST(#insertedRecords AS VARCHAR);
/* END */
--SELECT ##TRANCOUNT