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internal/store/migrations/0002_user_preferences.sql

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+-- Per-user interface preferences.
+--
+-- These live in their own table rather than as columns on users, because users is
+-- a projection of the identity provider's claims: UpsertUser rewrites it on every
+-- login. A row appears the first time somebody saves a preference and is keyed by
+-- the same subject, so the choice survives re-login and follows the account to
+-- another browser.
+--
+-- An empty selected_theme means the person has not chosen a theme, which the UI
+-- renders as its own default rather than as a stored value.
+--
+-- There is deliberately no foreign key to users. That table is a projection of the
+-- identity provider's claims and can be rebuilt from a backup, so a cascade from it
+-- would silently discard people's choices, and requiring the row to exist would make
+-- saving a preference depend on projection state that has nothing to do with the
+-- preference. A row whose subject never logs in again is inert and costs nothing.
+CREATE TABLE IF NOT EXISTS user_preferences (
+    subject             TEXT NOT NULL PRIMARY KEY,
+    selected_theme      TEXT NOT NULL DEFAULT '',
+    selected_appearance TEXT NOT NULL DEFAULT '',
+    updated_at          TEXT NOT NULL
+);
+
+-- Lets an operator answer "who is using this theme?" without scanning every row.
+CREATE INDEX IF NOT EXISTS idx_user_preferences_theme
+    ON user_preferences (selected_theme);