Render links reliably in Slack messages

[dwaxe]

Slack does not render [label](URL) input as a labeled link, so agents can post the literal syntax even though message send handles other Markdown-like formatting. Lists also force native rich_text, where bare URLs must be explicit link elements to remain clickable.

This normalizes HTTP(S) and mailto links for send/edit text, emits Markdown and bare HTTP(S) URLs as native links in converted rich text, preserves code, images, malformed input, and escaped links, and avoids swallowing sentence punctuation. The README and agent skill document the supported formats.

Validation

• bun test (432 tests)
• tsc --noEmit
• oxlint (0 errors)
• oxfmt --check on changed files

[maelvls]

fwiw, Slack renders <url|label>

[dwaxe]

Thanks @maelvls! Yep—that’s what this PR emits for ordinary message text. The additional path handles messages converted to rich_text blocks, such as lists and drafts, where links need native link elements. The latest commit covers bare HTTP(S) URLs in that path too.