Wraps up the code-review refactor pass.
- config/settings.py: ``download_source`` defaults gain
``album_bundle_poll_interval_seconds`` (default 2s) and
``album_bundle_timeout_seconds`` (default 6h, was a hard-coded
``6 * 60 * 60`` magic constant in torrent.py). The plugin reads
these via ``album_bundle.get_poll_interval`` /
``get_poll_timeout`` with safe fallback to the defaults when the
config value is missing / non-numeric. ``mode`` doc-comment
extended to list ``torrent`` and ``usenet``.
- core/downloads/validation.py: comment block above the album-name
fallback rewritten to document when the fallback actually runs
now — single-track hybrid downloads only, because the album-
bundle gate handles single-source mode and the hybrid chain
filter strips torrent / usenet from album batches. Code path
unchanged; just clarifies the contract for the next reader.
- webui/static/helper.js: WHATS_NEW entry summarising the refactor
pass (helper extraction, dispatch lift, staging deps injection,
atomic copy, configurable timeout, test additions).
The /loop of: extract → inject → test was sweep enough to drop the
gate code's coupling to 2-3 modules and put 49 unit tests behind
the new boundaries. Code-review feedback addressed:
1. album_bundle.py extracted ✓
2. Dispatch lifted out of master.py ✓
3. staging.py decoupled from runtime_state ✓
4. Validation fallback scope documented ✓
5. Poll timeout config-driven ✓
6. ``amazon`` provenance owned in a prior commit ✓
7. End-to-end-shaped tests added (test_album_bundle_dispatch.py)
8. Auto-Import race closed via atomic copy ✓
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