When bulk-closing tabs (e.g. "Close to the left"), the reconciliation
useEffect would re-add tabs for still-active agents before the server
archived them, causing tabs to flicker back then disappear one by one.
Adds hiddenAgentIdsByWorkspace as the inverse of pinnedAgentIds: a
local, in-memory-only override that prevents reconciliation from
re-opening tabs for agents the user just closed. Hidden intent is
automatically cleared when explicitly opening, retargeting, or pinning
an agent tab.
Mohamed Boudra
b9269df3e4