fix(seg): use buffer-based loader when PerFrameFunctionalGroupsSequence missing

[igoroctaviano]

Summary

Fixes SEG loading failures for DICOMweb servers that omit PerFrameFunctionalGroupsSequence from JSON metadata (like IDC's static WADO).

Root Cause Analysis

OHIF 3.13 changed SEG loading from:

• Old (3.12): createFromDICOMSegBuffer - fetches full DICOM file, parses complete metadata
• New (3.13): createFromDicomSegImageId - relies on metadata provider (DICOMweb JSON)

IDC's static WADO omits PerFrameFunctionalGroupsSequence from JSON metadata to save bandwidth (this sequence can be huge for SEGs with thousands of frames). The new loader fails because it expects this sequence.

Solution

Detect when PerFrameFunctionalGroupsSequence is missing and fall back to the buffer-based loader:

if (!hasPerFrameFunctionalGroups) {
  // Fetch full DICOM and use createFromDICOMSegBuffer
} else {
  // Use createFromDicomSegImageId (more efficient when metadata is complete)
}

This restores the behavior from OHIF 3.12 while keeping the optimized path for servers with complete metadata.

Upstream PRs

The fix and related improvements have been submitted upstream:

• fix(seg): fallback to buffer-based loader when PerFrameFunctionalGroupsSequence is missing OHIF/Viewers#6333 - fix(seg): fallback to buffer-based loader when PerFrameFunctionalGroupsSequence is missing
• fix(MergeDataSource): improve series-to-datasource routing for merged sources OHIF/Viewers#6331 - fix(MergeDataSource): improve series-to-datasource routing for merged sources

Patches Included

Also includes two backported patches from cornerstone3D that are still needed:

1. VOI LUT function validation (PR #2856)

   • Prevents "Invalid VOI LUT function" errors

2. Segment index by SegmentNumber for LABELMAP (PR #2882)

   • Fixes segment color mapping for LABELMAP with SegmentNumber=0

Closed Upstream PRs/Issues

The following were opened during investigation but are no longer needed since the fix is in OHIF:

• Issue OHIF V3 MPR OHIF/Viewers#2962 - Closed: checkOrientation null check (not needed)
• PR support for CSRF  OHIF/Viewers#2963 - Closed: PerFrameFunctionalGroupsSequence null checks (not needed)

Testing

1. Load a SEG from IDC that was previously failing
2. Verify segments display with correct colors
3. Verify CT/MR images render without VOI LUT errors