Composes the Phase 9 assistant primitives at /assistant: full-bleed chat
canvas with a 760px centered column, AssistantHomeGreeting for the no-
conversation state, AssistantInputBar + ActionStrip anchored at the
bottom, and HistorySheet / MemorySheet slide-overs. Drops the 160px
inner conversation-list column and the custom MessageBubble, delegating
thread rendering to the shared ChatMessageList and streaming to the
shared useStreamingChat hook. Adds a ?prompt= query-param fallback for
Studio → Assistant hand-offs, preserves the existing assistantHandoff
call as the Promote action, and syncs the selected conversation id with
the shared ChatPanelContext so HistorySheet stays in lockstep.
Also fixes typecheck fallout from the rewrite: switches toast tones to
the documented info|success|warn|error set, narrows the stale-project
filter to use archivedAt (ProjectStatus never had "archived"), and
tightens the MemorySheet test render helper to JSX.Element.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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