Cascading sub-format filter — 45s only (#370 Phase 2b, gated on #376)

[holden]

Context

Original #370 Phase 2 proposed a generic cascading sub-format facet under any selected Type. Live data audit shows that's not actually warranted: 3 of the 4 Types are effectively monolithic.

Type	Sub-format diversity
45s (14,710)	Real — 4 meaningful sub-types (Singles / Promo / EP / Gold Standard)
LPs (4,536)	95% in LPs: 10/12-inch; rest is mis-classified 12" Singles (handled by #376 reclassify)
Picture Sleeves (1,007)	99.5% in Picture Sleeves; one straggler
78s (123)	98% in Singles: 78 rpm; two stragglers

Conclusion: the only Type where a sub-facet pays for its UI cost is 45s. For the others, the sub-facet would render with one usable checkbox — pure noise.

Proposal

Replace the generic cascading sub-facet with a scoped sub-facet that appears only when 45s is the only active type pill. After #376 cleanup, the meaningful 45s sub-formats are:

Sub-format	Count
Singles: 7-inch	13,221
Promotional Singles	1,147
EPs: 7-inch	~280 (after merging the "45 rpm" typo)
Gold Standard Singles ('447' + 'GB')	46
Picture Disc Singles	15

A row of 5 sub-pills under the 45s pill, identical pill style to the existing Type/Confidence rows.

Sketch

TYPE        [ ✓ 45s 14,710 ] [LPs 4,536] [Picture Sleeves 1,007] [78s 123]
SUB-TYPE    [ All ] [Singles 13,221] [Promo 1,147] [EPs 280] [Gold Std 46] [Picture Disc 15]

The sub-pill row is hidden unless record_type_id_in == [45s_id] (single type, == 45s). Multi-select within the row uses a new param like record_format_id_in[].

If user adds another type to the selection (e.g. clicks LPs while 45s is active), the sub-pill row collapses (becomes ambiguous which type it scopes).

For LPs / Picture Sleeves / 78s

Don't surface anything in UI. Use the existing search box for granular queries (promotional, picture disc, etc.). Adding a 1-checkbox cascade is worse than no cascade.

Implementation notes

• New param: record_format_id_in[] (Ransack array, matches public/admin patterns)
• Controller: records.where(record_format_id: format_ids) when set
• Sub-pill visibility logic: server-side conditional in _filter_bar.html.erb, no JS needed
• Counts on the sub-pills should be live (after applying other filters) for usefulness — same query pattern as the Type pills
• Apply on both /records (public) and /admin/records (admin) — shared component if practical

Gating

Blocked on #376 (data cleanup). Without cleanup, the sub-pills row would still show typo dups (EPs: 7-inch and EPs: 7-inch 45 rpm as separate options) — defeats the purpose.

Out of scope

• Cascading sub-facets for other Types (intentionally not built; see analysis above)
• Search-as-you-type for sub-formats (orthogonal idea, not blocked by this)
• Schema changes (sub-format relationship is already correct)