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Pure stdlib http.server (ThreadingHTTPServer), zero third-party deps -- enforced by an AST-based test that parses backend_server.py's own imports and checks each against sys.stdlib_module_names, so this can't silently rot if someone adds a dependency later (05 §5.7). pick_folder(): macOS via `osascript 'choose folder'`; user-cancel maps to {"selected_path": null} (03-C §3.-1: not an error), non-macOS or any other osascript failure raises DialogUnavailableError -> HTTP 422 DIALOG_UNAVAILABLE. Windows/Linux native dialogs are PH3 (U-022). Known gap, noted rather than papered over: the Done criterion asks for a real popped dialog returning a real path, which needs an actual human click -- not something this agent can do non-interactively. Verified `osascript` itself is present and executes on this machine, and every code path is covered by mocked tests, but the literal "did a human click a real folder and get the right path back" check is still open for whoever runs this interactively next. 12 new stdlib unittest cases (server start/stop, pick_folder success/ cancel/non-macOS/other-failure, the same 4 cases through the HTTP route, zero-third-party-import check). 62 total across U-001-007 (60 real + 2 gated), all passing. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
