A freshly flashed device needed manual pip work before the reader would
start. It now checks its dependencies, installs whatever is missing, and
carries on.
- bootstrap.py: import check, pip invocation, and a re-check that does not
trust pip's exit code alone. Installs nothing when the libraries are
already present, so a normal start does no network work.
- --wheel-dir installs from local wheels with --no-index, for devices with
no internet. --no-install-deps opts out entirely.
- Outside a venv pip gets --break-system-packages, which Debian and
Raspberry Pi OS require before touching the system Python.
- reload_library() re-imports rdm6300 when it was installed at runtime, since
the module-level import already ran and failed.
- A failed install reports exit 2 and the exact manual command rather than
raising; stdout is flushed so the explanation is not printed after the
error when piped.
