Add performance indexes for leaderboard queries

Adds 4 indexes to speed up ranking and user queries:
- runs(submission_id) for ranking JOINs
- submission(leaderboard_id) for leaderboard filtering
- submission(user_id) for user lookups
- runs(submission_id, runner, score) partial index for ranking computation

Author: Mark Saroufim

src/migrations/20260225_01_aW5Bu-add-leaderboard-performance-indexes.py

@@ -0,0 +1,37 @@
+"""
+add-leaderboard-performance-indexes
+"""
+
+from yoyo import step
+
+__depends__ = {"20260108_01_gzSm3-add-submission-status"}
+
+steps = [
+    # FK index on runs.submission_id
+    # Used in every ranking query (JOIN runs ON submission_id = s.id)
+    step(
+        "CREATE INDEX IF NOT EXISTS idx_runs_submission_id ON leaderboard.runs(submission_id)",
+        "DROP INDEX IF EXISTS leaderboard.idx_runs_submission_id",
+    ),
+    # FK index on submission.leaderboard_id
+    # Every query filters WHERE leaderboard_id = X
+    step(
+        "CREATE INDEX IF NOT EXISTS idx_submission_leaderboard_id ON leaderboard.submission(leaderboard_id)",
+        "DROP INDEX IF EXISTS leaderboard.idx_submission_leaderboard_id",
+    ),
+    # FK index on submission.user_id
+    # Used in user trend, submission history, and user search queries
+    step(
+        "CREATE INDEX IF NOT EXISTS idx_submission_user_id ON leaderboard.submission(user_id)",
+        "DROP INDEX IF EXISTS leaderboard.idx_submission_user_id",
+    ),
+    # Partial composite index for ranking queries
+    # Covers WHERE NOT r.secret AND r.score IS NOT NULL AND r.passed
+    # Includes (submission_id, runner, score) for JOIN, PARTITION BY, ORDER BY
+    step(
+        "CREATE INDEX IF NOT EXISTS idx_runs_ranking"
+        " ON leaderboard.runs(submission_id, runner, score)"
+        " WHERE NOT secret AND score IS NOT NULL AND passed",
+        "DROP INDEX IF EXISTS leaderboard.idx_runs_ranking",
+    ),
+]