The PR relocates the concrete orchestration implementation from `ClientCore` in `_core.py` to `Session` in `notebooklm/_session.py`, and converts `_core.py` into a compatibility re-export shim for legacy private imports.
Scattered source updates, isolated context, and manual follow-up across multiple feeds.
Introduced a canonical internal implementation path (`_session.Session`) for session orchestration, updated package/docs/tests/fixtures/ADRs to reference it, and retained compatibility aliases and monkeypatch surfaces so existing private `_core` callers continue to work.
Developers and integrators relying on internal notebooklm behavior can keep legacy private flows working while the team starts using a single canonical session implementation path, which reduces accidental breakage when making internal changes. Public behavior is unchanged for `NotebookLMClient`, so immediate user-facing risk is low, but teams should continue watching for remaining private imports to `_core` and any monkeypatch-dependent paths that could diverge as future refactors move fully to the new layering.
Developers and integrators relying on internal notebooklm behavior can keep legacy private flows working while the team starts using a single canonical session implementation path, which reduces accidental breakage when making internal changes. Public behavior is unchanged for `NotebookLMClient`, so immediate user-facing risk is low, but teams should continue watching for remaining private imports to `_core` and any monkeypatch-dependent paths that could diverge as future refactors move fully to the new layering.