Require the Search Schema everywhere below it, and delete the schema-less degraded modes #767

What

Make the Search Schema a required, non-nullable argument everywhere below the schema on the write side, and delete the schema-less degraded modes it currently guards:

• physicalFields(field, schema) – the trigger for this issue: since feat(search): narrow a reference’s facet to the keys its target admits #765 the physical fanout is a function of (field, schema), not of the declaration alone (a facetable reference inheriting a facet policy facets its ${name}_facet companion, which only the schema can resolve).
• projectDocument(node, type, schema, context?) – drops the degraded reading “without a schema: no inline nesting, no re-keying, no facet companion”.
• buildCollectionDefinition(type, { schema, … }) – its two “needs the schema” throws for surfaced inline and joinable references disappear: what they guard becomes statically guaranteed.
• BuildSearchParamsOptions.schema – the compiler stops silently faceting the field itself and tokenising membership when the option is unset.
• The rebuild writers’ options (RebuildOptions), so new InPlaceRebuild(client, type) becomes new InPlaceRebuild(client, type, { schema }) – which the provenance-sweep guard added in feat(search): narrow a reference’s facet to the keys its target admits #765 already wants in order to do its job fully.

projectRoots and parseSearchResponse already require the schema; this extends their philosophy – “a function of the whole schema, exactly as the engine is” (the parseSearchResponse JSDoc) – to the rest of the surface, instead of leaving the package with two philosophies side by side.

Why

• The degraded modes have no user. No production path projects or builds a collection definition schema-less: the pipeline goes through projectRoots (schema required), and the engine, indexer and writers all hold one. The modes serve tests and a hypothetical library caller, for whom the ceremony after this change is one call: projectDocument(node, place, searchSchema(place)).
• Deleting the modes removes concepts rather than policing them. No “without a schema, X silently does not happen” caveats to document, no schema === undefined branches to cover, and the silently wrong physical field name bug class ceases to exist instead of becoming visible. feat(search): narrow a reference’s facet to the keys its target admits #765’s review caught a live instance of that class (the provenance-sweep guard judging facet status from the declaration); a required schema is the structural form of that fix.

Rejected: required-but-nullable

physicalFields(field, schema: SearchSchema | undefined) – every caller must write the argument, undefined stays legal. Considered first (and a smaller diff), but it keeps all three degraded modes and adds explicitness on top, and it is a second breaking change on the road to the same end state. If we pay a ! at all, pay it once for the simpler surface.

Scope and costs

• Two breaking commits: feat(search)! and feat(search-typesense)! (zero-major scheme: minor bumps).
• Mechanical test churn: ~70+ schema-less projectDocument/buildCollectionDefinition/physicalFields call sites gain a searchSchema(type) wrap.
• One edge to watch: searchSchema validates, so a test fixture that deliberately projects a type validation would reject needs rethinking.
• documentKeyOf, validateSearchType and the other pre-schema entry points are untouched – they are deliberately schema-free.