fix(layout): resize past neighbor minimum

[itsJai42]

Summary

Without this fix, when dragging Window B to resize it leftward, if Window A is at its minimum width, Window B will refuse to resize itself. This branch fixes that behavior, allowing Window B to be resized regardless of Window A's width. Note that this new behavior mimics what happens when you drag rightward to resize.

Type of Change

• Bug fix
• New feature
• Breaking change
• Refactoring
• Build / packaging
• Documentation

Testing

Commands run:

  meson setup build-debug -Dbuildtype=debug
  meson compile -C build-debug umbriel pointer-client scrolling-layout-test
  ./build-debug/scrolling-layout-test
  meson test -C build-debug --print-errorlogs scrolling-layout
  bash -n tests/harness/checks/516_resize_past_neighbor_minimum.sh
  tests/harness/verify.sh ./build-debug/umbriel 516_resize_past_neighbor_minimum
  git diff --check

Manual/integration testing:

• Ran the new headless compositor harness check 516_resize_past_neighbor_minimum.
• It opens two real foot windows, uses the virtual pointer with Mod+Right-drag to shrink A to its minimum, then drags B’s left edge left.
• It verifies A remains at minimum, B’s left edge moves left, and B’s right edge does not advance.

Manual Coverage

• Tested in a nested Umbriel session
• Tested in a native Umbriel session
• Tested with multiple monitors
• Tested with a scaled output
• Tested with native Wayland applications
• Tested with X11 applications through xwayland-satellite
• Tested with the scrolling layout
• Tested with the dwindle layout

Screenshots / Videos

2026-09-01.11-46-42.mp4

Checklist

• This PR is ready for review, or it is marked as Draft.
• This change fits SCOPE.md, or its scope was agreed in an issue or on Discord first.
• I read and followed the relevant guidance in CONTRIBUTING.md.
• I ran just format, or this PR has no C++ changes.
• I ran the relevant build, test, lint, or verification commands, or explained why they were not run.
• I functionally verified compositor behavior where automated checks are insufficient.
• I self-reviewed the changes.
• I checked for new warnings or errors.
• I updated docs/ and examples/config.toml, or this PR does not change user-facing configuration or behavior.
• I used canonical names for config keys, IPC actions, paths, and identifiers.