Closes #616: Add cursor pagination on /api/audit

drizzle/migrations/0025_audit_logs_cursor_index.sql

@@ -0,0 +1,20 @@
+-- Migration: 0025_audit_logs_cursor_index
+-- Replaces the single-column audit_logs_created_at_idx with a composite
+-- (created_at DESC, id DESC) index so that keyset-cursor pagination on
+-- GET /api/admin/audit is stable under concurrent inserts.
+--
+-- When two rows share the same created_at timestamp (common under high write
+-- concurrency) the previous single-column index left the tie-breaking order
+-- non-deterministic, meaning a page boundary could skip or repeat rows.
+-- The composite index makes (created_at, id) the canonical sort key, matching
+-- the ORDER BY and cursor predicate already used in auditLogRepo.ts.
+
+-- Drop the old single-column index (no longer needed).
+DROP INDEX IF EXISTS audit_logs_created_at_idx;
+
+-- Create the composite covering index used by the keyset cursor predicate:
+--   WHERE (created_at < $cursor_ts)
+--      OR (created_at = $cursor_ts AND id < $cursor_id)
+--   ORDER BY created_at DESC, id DESC
+CREATE INDEX IF NOT EXISTS audit_logs_created_at_id_idx
+  ON audit_logs (created_at DESC, id DESC);

src/db/schema.ts

@@ -403,7 +403,15 @@ export const auditLogs = pgTable(
     auditLogsCorrelationIdx: index("audit_logs_correlation_idx").on(
       t.correlationId,
     ),
-    auditLogsCreatedAtIdx: index("audit_logs_created_at_idx").on(t.createdAt),
+    // Composite index for stable cursor pagination: ORDER BY created_at DESC, id DESC.
+    // The (created_at, id) compound key is unique and monotone, so a keyset cursor
+    // over it is stable even when rows with the same timestamp are inserted
+    // concurrently — the id tie-breaker ensures no row is skipped or duplicated
+    // across page boundaries.
+    auditLogsCreatedAtIdIdx: index("audit_logs_created_at_id_idx").on(
+      t.createdAt,
+      t.id,
+    ),
   }),
 );