[flexdinesh]

• cmd/diffx scope resolution (checkoutSelection): bare diffx or one positional path inside a checkout now collects only that checkout; --scan-worktrees adds the repo's other registered worktrees. --path (any count) and non-checkout directories keep scanning by default. --scan-depth with a checkout path errors since there is no directory search to bound. Makes worktree scanning explicit where the user pointed at one checkout.
• collector.Workspaces{Paths, Depth, LinkedWorktrees}: replaces the positional paths, depth args of CollectWorkspaces/DiscoverWorkspaces; with LinkedWorktrees=false a repository contributes only the checkout containing its input. Sync reruns the same selection.
• Bootstrap contract: serverapp.Selection travels localserver.Input -> Collections -> Capabilities.Input(); input enum gains checkout (OpenAPI, generated types, readBootstrap).
• Web shell policy: shell-policy.ts gains reviewColumn (always remote, multiple local) and collection; the hook moves to use-shell-policy.ts so the policy stays node-testable. SessionProvider exposes a sticky reviewColumn flag: local mode shows the Reviews column, rail and compact drawer toggle once streamCount reaches 2, then keeps it for the page session. Search, comboboxes and sync stay. Sync reads "Sync checkout" for a single checkout.
• Docs: system.md, architecture.md, development.md, DESIGN.md, PRODUCT.md, user docs (usage.md, reviewing-changes.md). Impeccable diff workspace brief repointed to src/DiffWorkspace.tsx (was orphaned by a repo-root-relative path).
• Breaking: diffx inside a repo no longer collects sibling worktrees; use --scan-worktrees.
• Validation: mise run check:push (pre-push hook: full suites, race tests, generated drift) passes on the rebased branch.