Pasting a link whose text/html label is a shortened form of its URL plants a `[` inside the URL

Bắt đầu trong src/paste-markdown-html.ts, khoảng dòng 83-90, nơi convertToMarkdown xác định nhãn HTML trong văn bản thuần. Tái hiện trường hợp clipboard từ issue, sau đó thêm bốn bài kiểm thử hồi quy được mô tả trong bản sửa đề xuất và chạy bộ kiểm thử hiện có. Hoàn thành khi các nhãn URL rút gọn được thay thế chính xác mà không làm hỏng các URL, trong khi các trường hợp khác vẫn giữ nguyên hành vi hiện tại.

What happens

When a clipboard carries a URL as text/plain and an anchor labelled with a shortened rendering of that URL as text/html, pasting into a GitHub comment box inserts the Markdown link syntax inside the URL:

text/plain: https://github.com/owner/repo/blob/main/a.js#L7
text/html:  <a href="https://github.com/owner/repo/blob/main/a.js#L7">repo/blob/main/a.js#L7</a>

pasted:     https://github.com/owner/[repo/blob/main/a.js#L7](https://github.com/owner/repo/blob/main/a.js#L7)
expected:   [repo/blob/main/a.js#L7](https://github.com/owner/repo/blob/main/a.js#L7)

It renders as two links, one of them junk (https://github.com/owner/ on its own), and the comment has to be repaired by hand.

Reproduction

Run this in the console of any page with a GitHub comment box, press ⌘C/Ctrl+C, then paste into the box:

document.addEventListener('copy', event => {
  const url = 'https://github.com/owner/repo/blob/main/a.js#L7'
  event.clipboardData.setData('text/plain', url)
  event.clipboardData.setData('text/html', `<a href="${url}">repo/blob/main/a.js#L7</a>`)
  event.preventDefault()
}, {once: true})

Why it happens

convertToMarkdown starts from the plaintext flavour and splices [label](href) over the label at the offset where indexOf finds it:

https://github.com/github/paste-markdown/blob/main/src/paste-markdown-html.ts#L83-L90

That is correct for prose containing a link, where the plaintext is a flattening of the HTML. Here the plaintext is the URL and the label is a substring of it, so the label is found at offset 25 rather than 0 and the splice covers only the tail.

The same corruption happens when prose wraps the URL in punctuation — plaintext (https://github.com/owner/repo/blob/main/a.js#L7) yields (https://github.com/owner/[repo/…#L7](…)).

Who hits it

Any tool that writes a link to the clipboard as "URL as plaintext, shortened label as HTML" — macOS automation scripts (Hammerspoon/Alfred/Keyboard Maestro), clipboard managers, and "copy link" affordances that shorten the visible text. Labels containing a character the URL does not (repo#1234) are unaffected, because indexOf misses and the paste is left alone; every label that is a substring of its own URL is affected.

Proposed fix

#117 — replaces the whole URL when the label is a shortened rendering of it, declines rather than corrupting when the label sits inside a URL that is not its own href, and leaves every other case on the existing path. Four regression tests, all failing before the change.