Move the remaining manual import endpoint logic out of web_server.py and into core.imports.routes behind ImportRouteRuntime. The Flask endpoints now stay as thin compatibility wrappers for album/track search, album match/process, single-file import processing, and batched singles processing.
Keep legacy test patch points intact by re-exporting build_album_import_match_payload from web_server and routing singles_process through an injected process_single_import_file callable. This preserves existing route-level monkeypatch behavior while keeping the extracted helper testable.
Add focused helper coverage for Hydrabase enqueueing, search limit clamping, album match payload forwarding, album import side effects, single-file worker outcomes, malformed manual matches, and singles aggregation/injected-worker behavior.
Verification: py_compile and git diff --check passed locally; bundled-Python smoke covered the extracted helpers. Claude reran the project tests and reported all tests passing.
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