Fix icon cropping bugs, harden batch processing, add test suite

[matt-edmondson]

Summary

Fixes four defects in the image pipeline, stops one bad input from killing a batch, makes exit codes meaningful, and adds the repository's first test suite.

Bug fixes

• Crop off-by-one. The crop used right - left, but right and bottom are the inclusive indices of the last opaque pixel, so the span needs + 1. Every icon was losing its rightmost column and bottom row.
• Fully transparent input crashed the batch. With nothing opaque to measure, the bounds stayed inverted and produced a negative crop width, throwing an unhandled ArgumentOutOfRangeException that aborted the run and lost every icon queued behind it. ProcessImage now emits a fully transparent square instead.
• The output directory was not created if it did not already exist.
• Output extensions were wrong. Output is always PNG-encoded but reused the input file name verbatim, so a .jpg input produced a .jpg-named file containing PNG bytes. The extension is now rewritten to .png.

Batch resilience

A per-file failure of any type is now reported with its exception type name and skipped, so a locked or malformed file costs one icon rather than the whole run. Previously only three ImageSharp decode exceptions were caught and anything else propagated. ProcessDirectory returns a BatchResult of written and failed counts, and the summary line reports both.

Exit codes

Code	Meaning
0	All files processed, also --help and --version
1	Arguments unusable
2	Batch completed but at least one file failed

Both a failing batch and a missing required option previously exited 0.

Tests

Adds IconHelper.Test with 48 MSTest tests covering argument validation, the pixel pipeline, the file I/O layer and the exit code mapping.

The gold master tests run committed fixtures through the real ProcessDirectory path and compare pixel-for-pixel against committed expectations. regenerate.ps1 updates them, and two guard tests fail if a fixture or expectation goes unreferenced. Comparison is pixel-based rather than byte-based so an ImageSharp version bump does not cause false failures, with PNG bit depth and colour type asserted separately.

Supporting changes

Run is split into internal ProcessDirectory and ProcessImage, reached via InternalsVisibleTo, so the logic is testable. Output was verified byte-identical before and after that split. Also removes a dead local and its unused PointF alias, drops the unused ktsu.CaseConverter reference, and disposes the per-file Image that was leaking one instance per file.

Documents the recolouring algorithm inline, including the ImageSharp BlackWhite colour matrix it depends on. Rewrites README.md, which described an API (IconLoader, IconConverter, IconResolution, IconColorizer) that has never existed in this repo, and adds CLAUDE.md.

Test plan

• dotnet build -c Release clean, 0 warnings with warnings as errors enabled
• dotnet test -c Release passes 48 of 48
• Gold master proven to detect regressions by temporarily perturbing the algorithm, which failed 6 of 7 cases, then restoring
• All seven exit code paths verified against the real binary, not only unit tests
• End to end run over a directory mixing a valid PNG, a PNG locked by another process, a text file, a fully transparent PNG and a JPEG. All three valid files written, both failures reported, exit code 2

Note for reviewers

Every gold master expectation changed, because the crop fix alters the output of every icon. Sizes grew by one pixel where the result was not already clamped to the maximum. That is expected and the images are worth a look.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Ruh9nAQiuU5VGHV8uJCXtu

[sonarqubecloud]

Quality Gate failed

Failed conditions
D Reliability Rating on New Code (required ≥ A)
C Security Rating on New Code (required ≥ A)

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