feat: social graph features

migrations/0019_create_social_graph.up.sql

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+-- Social graph: follows, blocks, reports, plus a generic notifications
+-- table that backs the "notification plugin" (email today; websocket +
+-- push will read the same rows later).
+--
+-- Follows are REQUEST-BASED. Clicking "Follow" inserts a row with
+-- status='pending'; the target later accepts (status→'accepted',
+-- responded_at stamped) or rejects (row deleted). A user is "following"
+-- another only once the edge is 'accepted'. The UNIQUE(follower,
+-- following) pair makes a repeated request idempotent, and the CHECK
+-- stops anyone following themselves.
+CREATE TABLE IF NOT EXISTS follows (
+    id           UUID         PRIMARY KEY DEFAULT gen_random_uuid(),
+    follower_id  UUID         NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    following_id UUID         NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    status       VARCHAR(16)  NOT NULL DEFAULT 'pending',  -- pending | accepted
+    created_at   TIMESTAMPTZ  NOT NULL DEFAULT now(),
+    responded_at TIMESTAMPTZ,                              -- set when accepted
+    UNIQUE (follower_id, following_id),
+    CHECK (follower_id <> following_id)
+);
+
+-- "Who follows me / who has requested me" — the incoming side. Filtered
+-- by status so accepted-follower counts and pending-request lists are
+-- both index-served.
+CREATE INDEX IF NOT EXISTS follows_following_status_idx
+    ON follows (following_id, status);
+
+-- "Who I follow / who I've requested" — the outgoing side.
+CREATE INDEX IF NOT EXISTS follows_follower_status_idx
+    ON follows (follower_id, status);
+
+-- Blocks. blocker_id has blocked blocked_id. One row per direction; the
+-- service treats a block in EITHER direction as "these two can't follow
+-- each other" and tears down any existing follow edges both ways.
+CREATE TABLE IF NOT EXISTS user_blocks (
+    id          UUID         PRIMARY KEY DEFAULT gen_random_uuid(),
+    blocker_id  UUID         NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    blocked_id  UUID         NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    created_at  TIMESTAMPTZ  NOT NULL DEFAULT now(),
+    UNIQUE (blocker_id, blocked_id),
+    CHECK (blocker_id <> blocked_id)
+);
+
+-- Reverse lookup: "has anyone blocked me?" — used to compute blocked_by
+-- when rendering a profile.
+CREATE INDEX IF NOT EXISTS user_blocks_blocked_idx
+    ON user_blocks (blocked_id);
+
+-- Reports. A reporter flags another user with a category + free-text
+-- reason. resolved_at is one-way (admins clear it later); the partial
+-- index keeps the open-reports queue cheap to list.
+CREATE TABLE IF NOT EXISTS user_reports (
+    id           UUID         PRIMARY KEY DEFAULT gen_random_uuid(),
+    reporter_id  UUID         NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    reported_id  UUID         NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    category     VARCHAR(32)  NOT NULL,
+    reason       TEXT         NOT NULL,
+    created_at   TIMESTAMPTZ  NOT NULL DEFAULT now(),
+    resolved_at  TIMESTAMPTZ,
+    CHECK (reporter_id <> reported_id)
+);
+
+CREATE INDEX IF NOT EXISTS user_reports_reported_idx
+    ON user_reports (reported_id, created_at DESC);
+
+CREATE INDEX IF NOT EXISTS user_reports_unresolved_idx
+    ON user_reports (created_at DESC) WHERE resolved_at IS NULL;
+
+-- Notifications back the in-app/email/push fan-out. Today the
+-- NotificationService persists a row here AND sends an email; websocket
+-- + push delivery will later read unread rows for a user. actor_id is
+-- the user who triggered the event (nullable for system notifications);
+-- kind is a short machine string ('follow_request', 'follow_accepted').
+CREATE TABLE IF NOT EXISTS notifications (
+    id          UUID         PRIMARY KEY DEFAULT gen_random_uuid(),
+    user_id     UUID         NOT NULL REFERENCES users(id) ON DELETE CASCADE,  -- recipient
+    actor_id    UUID         REFERENCES users(id) ON DELETE CASCADE,           -- who caused it
+    kind        VARCHAR(32)  NOT NULL,
+    created_at  TIMESTAMPTZ  NOT NULL DEFAULT now(),
+    read_at     TIMESTAMPTZ
+);
+
+-- "My notifications, newest first" + an unread filter for badge counts.
+CREATE INDEX IF NOT EXISTS notifications_user_created_idx
+    ON notifications (user_id, created_at DESC);
+
+CREATE INDEX IF NOT EXISTS notifications_user_unread_idx
+    ON notifications (user_id) WHERE read_at IS NULL;