Gate r2 Low cleanups (house rule: no aliases/shims):
- Drop the is_live_database_file alias; its point-in-time caveat now lives on
has_live_connection.
- _refuse_live_database reuses offline_file_access's message (via _serve_offline),
so a download 409 on state.db-shm names the main database like the read path;
the verb is "serve" so it fits read/download/stream.
- /api/files/read reads whole files in-process, so _read_base64_file now holds
offline_file_access through close (409 on a live DB; OSError stays 500). Only
the streamed FileResponse routes keep the point-in-time check.
- That check takes the global _live_lock, which other threads hold across
whole-file reads, so fs_download and the managed stream routes run it via
asyncio.to_thread instead of stalling the event loop.
- _managed_readable_file docstring no longer claims a size cap;
_read_file_reference returns (early, text) instead of a str|Expansion union
sniffed with isinstance.
Co-authored-by: Benjamin PERRY <benjaminperry6@yahoo.fr>
fc53717f72