Copy the group
Right-click any tab group in Dia and choose Copy Links. That's the whole handoff.
How it works
Three steps, about ten seconds. Right-click the group, paste, and it's filed away.
Name it and place it
Paste into the popup, give the folder a name, and pick a spot from your full bookmarks tree. It remembers where you put the last one.
Tidy by default
Reads plain URLs, markdown links, or title-then-URL lines. Page titles are kept when they're there, and duplicates are skipped.
Why it works this way
Dia's tab groups are proprietary. They aren't visible to extensions — the chrome.tabGroups API is there but always comes back empty — and AppleScript only sees windows and tabs. The on-disk tab store is encrypted, so there's no file to read either.
Dia's own Copy Links command is the one door out, so the extension goes through it. In exchange, it asks for a single permission: bookmarks. Nothing reads your tabs, your history, or anything else.
Get it
A personal tool, built for my own Dia setup — not published to the Chrome Web Store.
Dia Tab Groups
Requires Dia (or any Chromium browser). Load it unpacked from chrome://extensions with Developer mode on. Source is on GitHub, in a private repo.