Two findings from the openchamber-bot review at 478f1e9c:
1. Pending selections silently swallowed the Open-in-Finder pick
(prev #4). handleOpenInFinder flows into the batch-first branch of
finalizeSelection, so with checkboxes ticked the OS pick was
ignored and the selections were added instead. Clear selectedPaths
before finalizeSelection so the Finder-sourced target is honored.
2. Within-batch dedup was missing in the VS Code branch (nit from
the previous review). A path repeated within one batch hit
addWorkspaceFolder twice. Mirror the non-VS Code contract with
a seen Set; add a regression test asserting the host is called
once per unique path.