-- MCP write provenance.
--
-- The remote MCP endpoint gains a confirmed write surface (logging a
-- measurement / mood). Rows it writes carry their own `MeasurementSource`
-- value so they are distinguishable from MANUAL / TELEGRAM provenance and
-- get an isolated idempotency namespace `(userId, type, MCP, externalId)`.
--
-- Purely-additive enum extension; no row touched. `ADD VALUE IF NOT EXISTS`
-- makes a rerun safe. The new value is NOT used elsewhere in this migration,
-- so it is safe to extend the enum in the same step (Postgres only forbids
-- USING a freshly-added value in the same transaction). Mirrors the 0189
-- source-extension that added TELEGRAM. The enum is `@@map`-ed to the
-- snake_case type name `measurement_source`.
ALTER TYPE "measurement_source" ADD VALUE IF NOT EXISTS 'MCP';