Don't splice a link into the middle of a URL

[pranayshirolkar]

Fixes #118.

Problem

Copy a link from a native app or a clipboard tool and paste it into a GitHub comment box, and the Markdown comes out with a [ planted in the middle of 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. The shape that triggers it — text/plain is the URL, text/html is an anchor labelled with a shortened rendering of that URL — is how a lot of tooling writes a link to the pasteboard (macOS automation scripts, clipboard managers, "copy link" affordances that shorten the visible text).

Cause

convertToMarkdown splices [label](href) over the label at the offset where indexOf finds it in the plain text:

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

That's right for prose containing a link — example link plus more text — because there the plain text is a flattening of the HTML. When the plain text is the URL and the label is a piece of it, the label is found inside the URL (offset 25 in the example above) and the splice covers only the tail.

Fix

When the label's occurrence sits inside a longer whitespace-delimited token, decide by what that token is:

• it is this link's own href — the label is a shortened rendering of the URL, so the link replaces the whole token. This produces the link the clipboard meant.
• it is some other URL — leave the paste alone. Splicing inside a URL is never right, and there is no sensible Markdown to emit.
• anything else — unchanged: the label's own occurrence is the span, so <a href="…">foo</a>bar pasted alongside foobar still yields [foo](…)bar.

areEqualLinks already handles the trailing-slash and casing differences between an anchor's normalized href and the pasted text, so the comparison reuses it.

Tests

Two added, both failing before this change and passing after (38 passed, 2 failed → 40 passed):

• links the whole url when the label is a shortened rendering of it
• doesn't splice a link inside a url that is not its own href

All existing tests pass unchanged.

[Copilot]

🟡 Changes recommended

Punctuation-wrapped URLs can still be corrupted because URL detection only checks the token’s first character.

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Pull request overview

Prevents shortened link labels from being inserted into the middle of pasted URLs.

Changes:

• Detects URL-containing plaintext tokens and selects a safer replacement span.
• Adds regression tests for matching and mismatched URLs.

File summaries

File	Description
src/paste-markdown-html.ts	Adds link-span detection and URL safeguards.
test/test.js	Adds regression coverage for shortened labels.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Balanced

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[pranayshirolkar]

@keithamus , can you take a look at this when you get a chance?