diff --git a/.gitea/workflows/ci.yml b/.gitea/workflows/ci.yml
index 312c576..1460e78 100644
--- a/.gitea/workflows/ci.yml
+++ b/.gitea/workflows/ci.yml
@@ -208,6 +208,33 @@ jobs:
       - name: Run DB migrations
         run: pnpm --filter @familysync/api db:migrate
 
+      # Seed the dev user (id=1). DEV_AUTH_BYPASS injects DEV_USER (id=1) into the request
+      # context in-memory only — it never writes a users row (devBypass.ts). global-setup.ts
+      # seeds calendars/lists/events for user_id=1 but ASSUMES that user row already exists
+      # (true on the dev DB, false on a fresh CI DB): without it the calendars INSERT IGNORE is
+      # silently skipped on the users FK, so calendar 10 is missing and the calendar_events
+      # insert fails its FK. Idempotent INSERT IGNORE; matches DEV_USER (oidc dev/dev-user, #4A90D9).
+      - name: Seed dev user (id=1)
+        run: |
+          node --input-type=commonjs - <<'EOF'
+          const mysql = require('mysql2/promise');
+          (async () => {
+            const conn = await mysql.createConnection({
+              host: process.env.DB_HOST,
+              port: Number(process.env.DB_PORT ?? 3306),
+              user: process.env.DB_USER,
+              password: process.env.DB_PASSWORD,
+              database: process.env.DB_NAME,
+            });
+            await conn.execute(
+              "INSERT IGNORE INTO users (id, oidc_iss, oidc_sub, display_name, color) VALUES (1, 'dev', 'dev-user', 'Dev User', '#4A90D9')",
+            );
+            console.log('seeded dev user id=1');
+            await conn.end();
+          })();
+          EOF
+        working-directory: apps/pwa
+
       # Build the API before starting it — dist/ is gitignored and does not exist in CI (Pitfall 4).
       - name: Build API
         run: pnpm --filter @familysync/api build