fix(inline): remove hl_mode combine from link extmarks to prevent ghost underlines

[ImmanuelHaffner]

The concealing extmark in link_hyperlink and link_image hides the ](https://…) portion of a link/image, which can span hundreds of bytes. With hl_mode = "combine" on that extmark, the virtual-text highlight (e.g. the link underline) bleeds across every concealed byte — so when the hidden URL is long enough to soft-wrap, Neovim's phantom screen rows get painted with "ghost" underlines/highlights.

Removing hl_mode = "combine" from the two conceal extmarks fixes it. (Comments added explaining why it must not be re-added.)

A fixture (test/inline_conceal_wrap.md) is included with a vim: set wrap linebreak modeline; open it in a narrow window and confirm no stray underline appears on wrapped rows below the link labels.

[OXY2DEV]

This is considered an unresolvable issue as not using hl_mode = "combine" breaks rendering when using certain combinations(mainly when non whitespace characters are used as paddings).

And the issue doesn't fully resolve with this as Vim's matchparen would still cause the highlights to bleed occasionally.

Until Neovim has resolved conceal related issues I don't think changing the hl_mode is the most desirable solution.

[ImmanuelHaffner]

What we make this a strict opt-in through config? I use it in my fork, and it works well. Definitely better than status quo.

We could have in the conf some

experimental = {
  link_conceal = 'combine',
}

or similar.

[OXY2DEV]

@ImmanuelHaffner What colorscheme are you using? I can't reproduce the issue on catppuccin, tokyonight & cyberdream.

[ImmanuelHaffner]

To reproduce set wrap, put cursor line on a cell with concealed text wrapping, e.g. long URL.
I can repro this independent of colorscheme (tested default and catpuccin and my night-owl fork).

It's also unaffected by set cursorline.

And i just realized that my attempted fix doesn't fix anything by itself. My larger table rendering PR doesn't have this issue. I need to see if i can file a localized, well justified fix for this issue without opening again this can of worms of table rendering.

[ImmanuelHaffner]

The issue manifests only on text on the cursor line, when set wrap is enabled, and when the table row is too wide for the window and is wrapped.
Only under these circumstances does the issue manifest.
Further, one needs to be in insert or visual mode or have hybrid mode enabled.

[ImmanuelHaffner]

Nailed it, the issue is linebreak. with set nolinebreak, the odd behavior is gone. and the ghost lines themselves are a neovim peculiarity that need fixing in the editor, IIUC.

[OXY2DEV]

@ImmanuelHaffner I still can't reproduce the issue on my machine.

Please create a repro.lua with the issue.