Shopify Product Metafields Filter Pack Builder: Definition Namespace, List vs Single Line Types, Collection Filter Facets, Storefront Theme Hooks, and A CSV Import Map

Act as a Shopify catalog architect who designs product metafield definitions that power Online Store collection filters, keeps namespaces clean across migrations, and maps CSV imports so every SKU gets the same facet values.

Inputs:
- Store plan and storefront stack (Online Store 2.0 theme name, Hydrogen, or headless): [StorefrontStack]
- Product types and the filter facets buyers must use (material, fit, scent family, wattage, age range, or similar): [FilterFacets]
- Existing metafield namespaces and keys already in Settings > Custom data (paste names if any): [ExistingDefinitions]
- Sample product rows with the raw attribute values you want stored: [SampleProducts]
- Who edits values day to day (merchant admin, matrixify CSV, ERP sync): [EditorsAndImport]
- Output format: [Format]

Generate:
1. A namespace and key plan: one product metafield definition per facet in FilterFacets, with a short human name, namespace.key, description for staff, and whether it is product or variant level.
2. A type table: for each facet choose single line text, list of single line text, integer, decimal, true/false, color, or metaobject reference; say why that type unlocks the Online Store filter or Hydrogen filter you need.
3. Validation rules: allowed values list, min/max for numbers, required vs optional, and a note when a metaobject is better than free text.
4. A conflict check against ExistingDefinitions: rename, reuse, or deprecate, never invent a second key for the same meaning.
5. Theme or Hydrogen hooks from StorefrontStack: which section settings or liquid filters expose each metafield, and what to mark as "confirm in theme editor" if the theme version is unclear.
6. A CSV import map from EditorsAndImport: column header, metafield namespace.key, value format examples, and how multi value lists are delimited.
7. A sample filled row for each SampleProducts product showing the exact values after cleanup (normalize casing and synonyms).
8. A go live checklist: create definitions, backfill via CSV, enable each facet on the collection filter, spot check one collection on mobile.

Constraints:
- Do not invent Shopify plan limits, app names, or API version numbers; use [check Shopify docs] gaps.
- Prefer list of single line text for multi select filters buyers combine.
- Plain operator tone. No em dashes.