feat(books): rename Locate button to Check WorldCat and use Check Options for search/carousels - #12914

👋 This branch was rebased onto current master to resolve merge conflicts, caused by #12910 merging in the meantime.

Why the conflict happened

#12910 ("show alternatives banner on unavailable book pages") merged just before this and heavily restructured openlibrary/macros/LoanStatus.html's conditional branches (moving from raw availability/book_provider checks to a single precomputed lending_state). Your branch renames LocateButton.html → CheckWorldcat.html and touches the same file's final $else: fallback block (the "not available anywhere" case) plus ReadButton.html, databarWork.html, and edition-sort.html — all files #12910 also modified.

The real conflict, reconstructed from your branch's actual intent vs. what's now on master:

1. LoanStatus.html def signature — master added lending_state=None; your branch renames the (previously declared-but-unused) is_book_page param to editions_page and starts actually reading it. Kept both: editions_page=False, ..., lending_state=None.
2. The $else: fallback block — master's version was structurally unchanged from your branch's base (just dropped one dead $ key = doc.key if is_edition else work_key line), so your intended two-way is_edition → editions_page ? CheckWorldcat : "Check Options" restructuring applied cleanly on top, using the edition_key that #12910 now computes earlier in the file (so the redundant local recomputation was dropped too).
3. databarWork.html — kept master's lending_state=lending_state and added your new editions_page=editions_page passthrough, so both PRs' additions to this call site survive.
4. edition-sort.html — kept master's lending_state=lending_state, dropped is_book_page=render_first per your branch's own diff (you removed that kwarg entirely at this call site as part of the rename).
5. messages.pot — regenerated fresh from the final rebased tree rather than hand-merged; only the Locate → Check options for this book. / Check Options string change survived, as expected.

Verified: git merge-tree against master is clean, make js builds with 0 errors, and I loaded a live book page in the dev environment to confirm LoanStatus.html renders correctly (200, no errors, "Check Options" link present).

Tip for next time: the earlier tip about rebasing periodically applies doubly here — this branch was open ~5 weeks and picked up drift not just from #12910 but from an unrelated earlier is_book_page param that had already gone dead/unused on master before your branch even started using it. Long-lived branches touching shared macros (LoanStatus.html, ReadButton.html) are worth rebasing every time a related PR merges, not just periodically.

No action needed — the branch is up to date with master and mergeable.

— PAM (Open Library's Project AI Manager)