Back MessageList with NSTextView for cross-row selection

[buggerman]

Summary

• Replace the SwiftUI LazyVStack { MessageRow } in MessageList and ServerMessageList with a new MessageBufferView: NSViewRepresentable wrapping NSScrollView + non-editable NSTextView.
• Restores mIRC-style drag-selection across any contiguous range of the chat buffer — across rows, across message kinds, and across every list (main chat, server console, detached window). Closes the gap flagged in Make chat content selectable and add Copy context menu #1's PR body.
• Preserves inline link previews: a new NSTextAttachmentCell subclass draws the same thumbnail + title + summary card that the old SwiftUI LinkPreviewView did, observable-wired to LinkPreviewStore.cache so it updates when a preview resolves.
• Ships as a stack on top of Make chat content selectable and add Copy context menu #1; review Make chat content selectable and add Copy context menu #1 first.

Changes

• Sources/Brygga/Views/MessageBufferView.swift — new file. NSViewRepresentable + Coordinator: NSObject, NSTextViewDelegate. Builds attributed storage per message (timestamp + sender + IRC-styled content), appends or full-rebuilds as appropriate, handles scroll pinning, wires a right-click menu with Copy Message / Copy Text / Copy Nickname. Private .bryggaMessageID attributed-string key tags each paragraph range so the menu handler can recover the clicked Message. Contains LinkPreviewAttachmentCell: NSTextAttachmentCell — draws a compact card with a thumbnail on the left and site/title/summary on the right, or fills the card with a direct-image URL's image. Preview observation uses withObservationTracking on LinkPreviewStore.cache; image bytes are fetched once per Coordinator lifetime with URLSession.ephemeral (10 s timeout, 2 MB cap, http/https only).
• Sources/Brygga/Views/ContentView.swift:
  • MessageList body reduced to a MessageBufferView(messages: visibleMessages, …, linkPreviews: appState.linkPreviews) call. visibleMessages filter logic unchanged. Marker index replaced with effectiveLastReadID passed through.
  • ServerMessageList body reduced similarly.
  • Both lists now depend on @Environment(AppState.self) to reach appState.linkPreviews and on @AppStorage(linkPreviewsEnabled) for the toggle.
  • Deleted: MessageRow, LineMarker, LinkPreviewView, firstPreviewableURL, _linkDetector — all dead after the swap. Net: −305 LOC in ContentView.swift.

What AppKit gives us for free

• Drag-select across rows — the thing that was missing in Make chat content selectable and add Copy context menu #1.
• ⌘A to select the whole buffer.
• Native ⌘C copy of the selection as plain text.
• Native incremental Find (⌘F) inside the NSTextView, in addition to the existing SwiftUI FindBar which still works as a channel-wide filter.
• NSTextView's default right-click menu (Look Up, Search, Share) augmented with our three Copy items.

Rendering notes

• Highlight lines render as an accent-colored .backgroundColor range; the 2pt accent-gutter stripe from the old MessageRow is gone — acceptable visual simplification, can be restored later via a paragraph-block border if the maintainer wants it back.
• The "new" divider is a centered "── new ──" paragraph inserted after the last-read message.
• Nick colors round-trip to NSColor via NSColor(Color) — the shared NickColor.color(for:) palette still drives both.
• Scroll pinning follows mIRC: append scrolls to the bottom only if the user was pinned there before the append; otherwise their scroll position is left alone.
• Link preview cards are indented under the message body (firstLineHeadIndent: 68) so they line up beneath the content, not beneath the timestamp column. Clicking anywhere on the card follows the URL.

Pure-Swift policy

AGENTS.md forbids introducing Obj-C, bridging, or @objc on new APIs. This change uses AppKit classes (NSTextView, NSScrollView, NSFont, NSColor, NSMenu, NSTextAttachment, NSTextAttachmentCell, NSBezierPath) — already the pattern elsewhere in the repo (see BryggaApp.swift, PreferencesView.swift). There is one @objc private func copyAction(_:) inside the private Coordinator; it's a selector callback required by NSMenuItem's target-action contract — not a new public API surface. If that counts as a violation per your reading of the rule, tell me and I'll drop the custom menu items and rely on NSTextView's default context menu alone (the native Copy on a selection still works).

Test plan

• swift build — passes
• swift test — 88 tests pass (unchanged; all existing tests still green, MessageBufferView has no new unit tests because it's view-level AppKit code)
• swiftformat --lint . — clean
• Scripts/build-app.sh — builds build/Brygga.app fine
• Manual (required, I cannot drive the UI from here):
  • Point Brygga at a busy channel (local ergo, Libera, whichever).
  • Drag across several messages spanning multiple rows. ⌘C. Paste into TextEdit. Confirm a multi-line log-style block is on the clipboard — this is the thing that was broken in Make chat content selectable and add Copy context menu #1.
  • ⌘A inside the chat buffer → select all → ⌘C → paste. Confirm the whole visible buffer comes out as plain text.
  • Right-click a message → verify Copy Message, Copy Text, Copy Nickname each place the expected string on the clipboard (unchanged behaviour from Make chat content selectable and add Copy context menu #1, now served by the NSTextView menu).
  • Paste a URL with OG tags (e.g. a news article) into a channel — confirm the preview card appears under the message once the fetch completes, with thumbnail + site / title / summary. Click the card → URL opens.
  • Paste a direct-image URL (e.g. https://i.imgur.com/abcd.png) — confirm it renders as an inline image capped at 420×240.
  • Click a URL in a message — the link opens in the default browser.
  • Type in a busy channel — confirm auto-scroll follows new messages when the user is at the bottom, but does not snap back if the user scrolled up to read history.
  • Set a highlight keyword in Preferences and trigger a highlight — confirm the highlighted line has an accent-tinted background.
  • Leave a channel and come back — confirm the "── new ──" divider appears above the first unread message.
  • Repeat the drag-select test in the server console tab and in a detached channel window (⌘⇧D).
  • Toggle Show joins/parts in Preferences — verify presence traffic hides/shows; no crash on full rebuild.
  • Toggle Colorize nicknames and switch Timestamp format — verify the buffer re-renders with the new attributes.
  • Toggle Fetch link previews off — confirm existing cards stay visible from cache but new URLs produce no card. Toggle back on — new URLs fetch.

Risk / rollback

Medium. This replaces the hottest UI path with an AppKit-backed view. The scroll pinning, incremental append, full-rebuild paths, and observation/fetch paths are all new code. Revert the commits if any manual check fails; PR #1's per-row selection + Copy menu remains in place independently.