[TheGreatAxios]

Summary

• Sidebar chat rows, the chat transcript, and the room timeline/participant list now render a real avatar in every .shell-ch-avatar slot: CorbitAvatar for agents, a pastel initials chip (hashed off the principal id via avatarColorForPrincipal/avatarClassForPrincipal) for people — via a new shared IdentityAvatar helper in apps/web/src/chat/avatar.tsx.
• Restored the sidebar reply-ready indicator: a chat's newest turn is tracked (ChatSummary.lastAuthor/lastMessageId in apps/web/src/chat/threads-api.ts), and an unseen agent reply shows the existing .shell-ch-completion check badge plus a polite live-region announcement, clearing when the chat is opened (markChatSeen, tracked per-viewer in localStorage).
• The CSS for the orbit/completion indicators and reduced-motion collapse in apps/web/src/app.css was already present on this branch (from the original PR's changes surviving); no CSS changes were needed.

Not implemented

• The "agent turn in flight" (orange orbit) indicator is not restored: no signal for it is derivable from the mailbox data the client reads (ChatAgent/mail turns carry no in-flight/pending state). Only the reply-ready half of the original indicator is implemented, as called out in the task.

Verified

• bunx tsc -p apps/web --noEmit
• bun run lint
• bun run fmt
• cd apps/web && bun run build
• cd apps/web && bun test ./src (584 pass) — note: bun test apps/web/src from the repo root fails on DOM globals because it skips apps/web's bunfig; running from apps/web (or via bun run test, which builds first) is required.

Not verified

• No manual browser check (dev stack was not started per instructions).

Worth upstreaming to corbitsdev/react-ui

• IdentityAvatar (agent-vs-person avatar resolution) and the underlying CorbitAvatar/avatarColorForPrincipal pastel-initials pattern in apps/web/src/chat/avatar.tsx look like a reusable "identity avatar" primitive rather than workbench-specific composition.

[linear-code]

CL-8475