Cancel abandoned loads, surface expansion failures, apply MIF scaling

[marcoduering]

Summary

Three fixes, one commit each. Independent of #2 (branched from main); both touch MiqParser.ParsePartial, so whichever merges second will need a small conflict resolution there.

1. First load could not be cancelled

Plugin.View called MiqParser.ParsePartial(path) without a token and checked cancellation only after the full read/decompress. Arrowing through large files left every abandoned load running to completion (CPU, I/O and memory for files no longer on screen).

• ParsePartial(string, CancellationToken ct = default) threads the token through the full-parse fallbacks, the volume-0 reads (ReadFully) and GunzipPartial.
• Reads are chunked at 4 MB so the token is checked during multi-GB reads, including the managed Gunzip loop.
• Cancellation escapes the partial-load fallback catch blocks instead of triggering a full parse.
• Plugin.View passes cts.Token and ignores OperationCanceledException after nav-away.

Remaining gap: the libdeflate path's File.ReadAllBytes of the compressed file is not interruptible (the token is checked just before it).

2. Background expansion failures were swallowed

StartExpansion caught every exception, so an out-of-memory, I/O error or changed file left the scrubber on "loading…" forever with no retry. Now only cancellation is ignored; any other failure calls MiqTriPlanarControl.ExpansionFailed. That keeps volume 0 visible, shows "first volume only (full load failed)" (new ScrubMode.Failed), and puts the exception message in the tooltip.

3. MRtrix MIF scaling: field was ignored

MifParser hard-coded SclSlope/SclInter to 0. It now maps scaling: offset,scale (value = offset + scale × stored) to SclSlope = scale, SclInter = offset. The voxel readout and Scaling metadata row are now correct, negative scales no longer invert the image, and scaled data no longer passes the identity-scaling check for segmentation colouring. Absent, identity, malformed, non-finite or zero-scale values stay unscaled; the optional field never fails the parse.

Tests

• ParseCancellationTests (non-parallel collection, because one test lowers PartialLoadThreshold): a pre-cancelled token throws on the multi-volume .nii.gz partial path, single-volume .nii.gz full path, small .nii full path and large .nii volume-0 path, and each file still loads without a token. Also covers GunzipPartial directly.
• MifScalingTests: scaled voxel value, Scaling metadata text, segmentation colouring disabled by scaling (with an unscaled control that does colour), and six absent/unusable variants that stay unscaled.
• The expansion-failure UI lives in the plugin project, which has no test project, so it is not covered by automated tests.

Not yet built or run: the authoring environment had no .NET SDK (download blocked by network policy), and CI builds only the plugin, not MIQ.Tests. Please run dotnet build and dotnet test locally before merging. It is also worth confirming the offset,scale order against a real mrconvert output with non-identity scaling.

🤖 Generated with Claude Code

https://claude.ai/code/session_01XqBwhnTRsqxk3SEvp9z4T9

---

Generated by Claude Code