-- 0051_discover_tuning.up.sql — tunable knobs for the Discover request
-- surface (#2377, milestone #268 slice 6).
--
-- A FOURTH tuning scope alongside radio / daily_mix / taste. Its own scope
-- rather than extra columns on taste_tuning, for a reason that matters:
-- snooze_days lives here, and a snooze must never be read as taste signal
-- (#2374). Filing it under 'taste' would put it one careless join away from
-- exactly the leak that design forbids.
--
-- Per rule #25 these are DB-backed and editable in the admin UI with no
-- restart — the shipped values below are defaults, not settings.
CREATE TABLE discover_tuning (
    singleton          boolean PRIMARY KEY DEFAULT true
        CONSTRAINT discover_tuning_singleton_check CHECK (singleton),
    -- How strongly taste-tag overlap boosts a candidate's similarity score.
    -- The blend is MULTIPLICATIVE: score * (1 + w * overlap), overlap in
    -- [0,1]. So 0 disables the feature outright and leaves pure similarity
    -- ranking, 1.0 lets a perfectly-matching candidate double its score, and
    -- a candidate with no cached tags is unchanged rather than penalised
    -- (rule #131 — tag coverage is permanently partial, see #2376).
    tag_overlap_weight double precision NOT NULL,
    -- Default snooze duration in days. Was a Go constant in
    -- internal/api/suggestions.go; moved here per rule #25.
    snooze_days        double precision NOT NULL,
    updated_at         timestamptz NOT NULL DEFAULT now()
);

INSERT INTO discover_tuning (singleton, tag_overlap_weight, snooze_days)
VALUES (true, 1.0, 90);

-- Rule #36: a new value for a CHECK-gated column needs the constraint
-- rewritten in the SAME change, or the first audit row written under the new
-- scope fails at runtime rather than at migrate time.
ALTER TABLE recommendation_tuning_audit
    DROP CONSTRAINT recommendation_tuning_audit_scope_check;
ALTER TABLE recommendation_tuning_audit
    ADD CONSTRAINT recommendation_tuning_audit_scope_check
    CHECK (scope IN ('radio', 'daily_mix', 'taste', 'discover'));