@username tokens in a sent message are parsed against the room's actual
members (skipping fenced/inline code, so pasted code isn't misread) and
recorded as MessageMention rows, reusing #38's read-tracking and
offline-member broadcast infrastructure rather than building a parallel
notification path:
- Sidebar: a mentioned-and-unread room shows a distinct highlight-
colored badge instead of (not alongside) the plain unread dot --
computed the same way as has_unread, just scoped to messages that
mention the caller, and cleared by the same last_read_at mark-read
flow.
- Push notifications: a mentioned offline recipient gets "X mentioned
you: ..." instead of the generic "X: ...", still per-recipient since
the same message can page some room members and not others.
- Message rendering: a validated @username is highlighted inline,
implemented by turning it into a `[@username](mention:username)` link
before markdown parsing and overriding link rendering to style
`mention:`-scheme links as a span instead of an anchor -- reuses
markdown-to-jsx's existing parser rather than hand-rolling text-node
splitting.
- Composer: typing @ opens an autocomplete dropdown of matching room
members (arrow keys to navigate, Enter/Tab/click to insert, Escape or
moving the cursor away to dismiss).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
