feat(composer): wrap selection on buzz:// link paste

[tellaho]

Overview

Category: improvement
User Impact: Highlighting text in the chat composer and pasting a buzz:// link now wraps the selection in a hyperlink — exactly like pasting a standard https:// link.

Problem: Pasting a buzz:// URL over a text selection replaced the highlighted text with the raw URL instead of turning it into a link. Standard https:// links already wrapped-on-paste, so the inconsistency was confusing.

Solution: TipTap's built-in linkOnPaste handler detects URLs with linkifyjs, which only knows standard schemes (http/https/mailto) — it has no idea buzz:// is a URL, so the wrap-on-paste handler bailed. This adds a custom ProseMirror paste plugin (prepended before TipTap's defaults) that recognizes any well-formed buzz:// URL and wraps the highlighted selection in a link mark. Per tho's direction, all buzz:// URLs wrap, not just the buzz://message?... deep-link format.

File changes

desktop/src/features/messages/lib/messageLink.ts
Added isBuzzUrl() — a broad check (via the URL API) for any well-formed buzz:// URL, distinct from the existing message-link-only isMessageLink().

desktop/src/features/messages/lib/useRichTextEditor.ts
Extended the Link extension's addProseMirrorPlugins with a buzzLinkOnPaste plugin that wraps a non-empty selection in a link mark when the clipboard payload is a single buzz:// URL. Runs before the parent plugins so it claims the paste; otherwise defers to TipTap's defaults.

desktop/src/features/messages/lib/messageLink.test.mjs
Added coverage for isBuzzUrl(): message links, non-message buzz:// URLs, whitespace tolerance, and rejection of standard/malformed/empty input.

Reproduction Steps

1. Run the desktop app and open the chat composer.
2. Copy a buzz:// URL (e.g. buzz://message?channel=...&id=...).
3. Type some text, highlight a portion of it, and paste.
4. The highlighted text becomes a hyperlink pointing at the buzz:// URL (previously it was clobbered with the raw URL text).
5. Repeat with a standard https:// URL to confirm existing behavior is unchanged.

Testing

• pnpm typecheck ✅
• pnpm lint ✅ (only pre-existing warnings in unrelated e2e files)
• pnpm test ✅ 720 passing

[tellaho]

Closing as redundant — the behavior this PR adds already exists on main.

Why

The composer's Link extension on main is configured with protocols: ["buzz"] + linkOnPaste: true (landed in the "Rename to Buzz" PR #960, June 11). Verified against the installed @tiptap/extension-link@3.22.5 source:

1. onCreate calls registerCustomProtocol("buzz") for each entry in protocols — so linkifyjs does recognize the buzz:// scheme.
2. The built-in linkOnPaste handler checks for a non-empty selection, runs the paste through linkifyjs find(), and if the whole payload is a single link, calls setMark(...{ href }) to wrap the selection.

That is line-for-line what this PR's custom buzzLinkOnPaste ProseMirror plugin re-implements. Confirmed empirically: pasting a buzz:// URL over highlighted text on main already hyperlinks the selection.

Correction

The original root cause ("linkifyjs doesn't recognize buzz://, so the selection gets clobbered") was incorrect — protocols: ["buzz"] teaches linkifyjs the scheme, and #960 quietly fixed this for free. The PR was built against a problem that no longer existed.

Scope check

Diff of the branch's own two commits (b2ad3074..HEAD) touches only the 3 feature files (messageLink.ts, messageLink.test.mjs, useRichTextEditor.ts) — no unrelated fixes were packed in, nothing else lost by closing.

Still worth landing separately

The biome dead-code cleanup (the latent noUnusedVariables debt in onboarding.spec.ts that surfaces under PR-context lint) is being tracked as its own standalone PR to main — independent of this one.