What switching Semantic search on (or to another embed model) would cost ONE existing column, in credits, before the save: the backfill now (cost_expected over cells_to_embed of cells_filled; text already embedded with the same model is free) and one new or edited value later, as a range (cost_per_value_min to cost_per_value_max: a later value is its own call and its length is unknown until it lands). A dry run of the embed job's own sweep priced by the catalog rule, at the platform key every call runs on. No writes, no charges. Surface the numbers to the user before update_playtable_field sets payload.semantic_index.

Contract:

• MCP tool estimate_semantic_index, registry package mcp.playtables/playtable_fields, mount playtables.columns.
• Operation action, response envelope action.
• Flags: read only.