fix: Prevent silent field overwrite when mapping conflicting fields to PostLabelingDelay

[Devguru-codes]

In ASLProcessor._rename_fields, field_mappings maps both InversionTime and InitialPostLabelDelay to PostLabelingDelay. If a parsed session dict contains both fields with different values, the loop previously overwrote the first parsed mapping with the second mapping silently, resulting in data loss. This could silently change physical scan properties like PLD.

Fix

Added a conflict detection check to the field mapping loop:

• If the target key already exists and the new source value is different, it logs a warning and retains the existing key/value rather than overwriting it.

File Changed

package/src/pyaslreport/modalities/asl/processor.py

         for old_key, new_key in field_mappings.items():
             if old_key in session:
-                session[new_key] = session[old_key]
+                if new_key in session and session[new_key] != session[old_key]:
+                    import logging
+                    logging.warning(
+                        f"Field conflict: '{old_key}' ({session[old_key]}) maps to '{new_key}' "
+                        f"which already has value {session[new_key]}. Retaining existing '{new_key}'."
+                    )
+                else:
+                    session[new_key] = session[old_key]
                 del session[old_key]

---

API/Processor JSON Responses Comparison

When sending the following payload to the FastAPI /api/report/process/bids endpoint:

{
  "InversionTime": 1.5,
  "InitialPostLabelDelay": 2000.0,
  "RepetitionTime": 4000.0,
  "MagneticFieldStrength": 3.0,
  "MRAcquisitionType": "3D",
  "Manufacturer": "Generic"
}

main branch (before fix)

The API normalizes the parameters silently losing the 1.5 value:

{
  "MagneticFieldStrength": 3.0,
  "MRAcquisitionType": "3D",
  "Manufacturer": "Generic",
  "RepetitionTimePreparation": 4000.0,
  "PostLabelingDelay": 2000.0
}

Result: The InversionTime of 1.5 is silently overwritten and lost.

issue10 branch (after fix)

The API correctly spots the conflict and retains the first value (1.5), logging a warning:

{
  "MagneticFieldStrength": 3.0,
  "MRAcquisitionType": "3D",
  "Manufacturer": "Generic",
  "RepetitionTimePreparation": 4000.0,
  "PostLabelingDelay": 1.5
}

Server logs WARNING:

WARNING:root:Field conflict: 'InitialPostLabelDelay' (2000.0) maps to 'PostLabelingDelay' which already has value 1.5. Retaining existing 'PostLabelingDelay'.

---

Python API Suite Results

main branch (before fix)

#	Test	Status	Detail
1	InversionTime only -> PostLabelingDelay	PASS
2	InitialPostLabelDelay only -> PostLabelingDelay	PASS
3	Both fields with diff values -> silent overwrite	FAIL	PLD=2000.0 (1.5 silently lost)
4	Both fields with same value -> no data loss	PASS

Summary: PASSED=3 FAILED=1

issue10 branch (after fix)

#	Test	Status	Detail
1	InversionTime only -> PostLabelingDelay	PASS
2	InitialPostLabelDelay only -> PostLabelingDelay	PASS
3	Both fields with diff values -> silent overwrite	PASS	Retains 1.5, logs warning
4	Both fields with same value -> no data loss	PASS

Summary: PASSED=4 FAILED=0

---

Sanity Checks

Check	Result
Pytest suite passed	Yes

Resolves #11