fix(layout): preserve explicit width when resizing a single column

[itsJai42]

Summary

Allow a single scrolling-layout column to keep an explicitly selected width when expand_single_column is enabled.

New columns still expand to fill the workspace. Pointer resizing, width actions, and width preset cycling now mark the column as user-sized so automatic expansion no longer overrides its width. This state is preserved when the layout is captured and restored.

Motivation

With expand_single_column = true, tiled windows (in my case, Steam/Spotify) could not be resized horizontally. The resize changed the stored width, but the layout immediately expanded the column back to the full workspace width. To me, this seems more like a bug than a design decision.

Type of Change

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

Testing

• meson compile -C build-debug
• meson test -C build-debug --print-errorlogs
  • 52 tests passed
• tests/harness/check.sh build-debug/umbriel 410_drag_width 516_resize_past_neighbor_minimum 517_expand_single_resize
  • 3 checks passed
• Added unit coverage for:
  • Preserving automatic expansion after initial width seeding
  • Allowing pointer resizing to override automatic expansion
• Added a headless compositor check that confirms a lone column starts expanded and remains at its resized width after a right-edge drag.

Manual Coverage

• Tested in a nested Umbriel session
• Tested in a native Umbriel session
• Tested with native Wayland applications
• Tested with X11 applications through xwayland-satellite
• Tested with the scrolling layout

Screenshots / Videos

2026-09-05.18-34-55.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.

Additional Notes

The original problem was observed with X11 applications through xwayland-satellite. The regression check uses a native Wayland client to exercise the same scrolling-layout resize path.