The native-OS-chooser backend of the directory-picker seam: NativeDirectoryPicker registers ctx.directoryPicker with the native capability, whose pick(signal) opens one native chooser per call and resolves the chosen absolute path (null on cancel). Platform tools run without a shell: osascript on macOS and Zenity with a KDialog fallback on Linux; the caller's abort terminates the native process. Windows opens the modern IFileOpenDialog in a spawned child process — a koffi-driven COM conversation on the child's main thread with the best thread DPI awareness the host accepts (per-monitor-v2 first), aborted by posting WM_CLOSE to the dialog thread. Only viable when the operator sits at the host's display — remote deployments compose -browse instead. The command boundary (DirectoryPickerRunner) and platform facts are injectable for deterministic tests. The shared no-shell subprocess runner lives in dsh-native-command.

Dual-face package: the browser half (./client) registers a renderless flow occupant into ui-workspace's two directory-flow holes — each open request drives host.pickDirectory and reports the one outcome (picked path / cancel / failure) through the hole's owner conversation. One cordis.yml row therefore composes both sides of the native interaction; the client carries no capability-kind branching, and mounting a second flow package fails at load (the holes are single kind).

Model Experience

None, as the backend serves the GUI host's directory selection; nothing here reaches a model request.

KV Cache effect

None; this package neither assembles nor sends a provider request.

Known Limitations and Deferred Work

Linux requires desktop tooling — with neither Zenity nor KDialog installed, pick rejects with an actionable error; it does not fall back to a typed-path prompt (the browse backend is that fallback at the composition level).
Windows has no mechanism fallback — the child-process picker is the only tier: koffi is a packaged dependency whose availability the install guarantees, so a failed pick (COM refusal, dialog crash) surfaces the failure instead of degrading to a PowerShell-hosted dialog (the former pwsh → Windows PowerShell 5.1 chain was removed). The browse backend remains the fallback at the composition level.