Add withDb() helper for graceful DB error handling

Shared withDb() wrapper in @trails-cool/db catches database
connection errors and throws a 503 Response instead of crashing
the server. Re-throws React Router responses (redirects, data()).

Applied to Planner session routes — replaces manual try/catch.
Any route can use withDb(() => ...) for automatic 503 on DB failure.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/db/src/index.ts

@@ -14,4 +14,28 @@ export function createDb(connectionString?: string) {
 
 export type Database = ReturnType<typeof createDb>;
 
+/**
+ * Wraps a route handler (loader/action) to catch database errors
+ * and return a 503 Service Unavailable instead of crashing.
+ */
+export function withDb<T>(handler: () => Promise<T>): Promise<T> {
+  return handler().catch((error) => {
+    if (error instanceof Response) throw error; // Re-throw React Router responses (redirects, data())
+    const message = error instanceof Error ? error.message : "Unknown error";
+    if (
+      message.includes("connect") ||
+      message.includes("ECONNREFUSED") ||
+      message.includes("DrizzleQueryError") ||
+      message.includes("AggregateError") ||
+      message.includes("database")
+    ) {
+      throw new Response(JSON.stringify({ error: "Database unavailable" }), {
+        status: 503,
+        headers: { "Content-Type": "application/json" },
+      });
+    }
+    throw error;
+  });
+}
+
 export { plannerSchema, journalSchema };