style: braces always, concat over interpolation

AGENTS.md

@@ -9,6 +9,19 @@ Applies to every change in this repo, by any agent or human.
 - Single quotes where possible
 - Functions as `const fn = () => {}` where possible
 - No trailing commas before a closing `}`, `]`, `)` (`trailingCommas: none`)
+- Always use braces for `if`/`else`/loop bodies — never single-line bodies like
+  `if (x) return y`. Write:
+
+  ```ts
+  if (typeof value === 'bigint') {
+      return value.toString()
+  }
+  ```
+
+  (Biome `useBlockStatements` enforces this)
+- No template-literal interpolation for building strings: use concatenation —
+  `'[' + engine + '] ' + message`, NOT `` `[${engine}] ${message}` ``.
+  Plain multi-line template literals WITHOUT `${}` (e.g. SQL text blocks) are fine.
 - Biome enforces all of the above — run `npm run lint:fix` before every commit
 - Line width 100