Test-side catch-up with the session-maybe conversation architecture: the
provide channel's descriptor shape and maybeProvideInfo in fakes, the shared
chat-store handle asserted on conversation.session (the session-maybe shell
carries no store), startSession fakes exposing the workspace list snapshot,
strict session slots declining (not throwing) without a session, AppFrame's
removed empty seat and loading gate, and the hero draft asserted on the
machine (the chat-store mirror binds with ConversationSession). Plus three
lint fixes (max-len split, boolean-compare, arrow-parens/unbound-method).
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