RV-F12: T&E row errors point to wrong source record numbers (survivor-list position) #189

What happened

External repo review at commit c7bebd1 reproduced: rows failing client-side casting are removed before DB insertion; DB errors then use the survivor-list position as the row number. Reproduced: invalid number in data row 1 and invalid foreign key in data row 2 both reported as row 1.

Code path: api/services/te_loader.py L273–290.

Why this matters

The error report tells the user "row 1 failed FK validation" when it was actually row 2. For a reviewer looking at a 10,000-row file, this makes the error report unusable — the row numbers in the error message don't match the row numbers in the source CSV.

Interacts with M4 review screen (#142 shipped) which displays row-level errors — review currently shows the wrong row for FK/CHECK failures.

Proposed

1. Retain original CSV row number alongside each candidate throughout validation and batching.
2. DB-error path reports the stored original row number, not the survivor-list position.
3. Reproduction test: CSV with row 1 invalid number and row 2 invalid FK; error report must show "row 2 failed FK", not "row 1".

Done when

• Reproduction test passes.
• Review screen shows correct row numbers for both client-side casting failures and DB-side constraint failures.
• Regression test: pre-existing error cases still show correct row numbers.

Reference

Tracker row G55. Repo review finding RV-F12. Interacts with M4 review screen (#108, #142, #143 already shipped). Should land before clients review real T&E uploads.