Update CLAUDE.md.

CLAUDE.md

@@ -50,3 +50,32 @@ LEFT JOIN cuisine_translations ct ON ct.cuisine_slug = c.slug AND ct.lang = $lan
 
 When adding a new entity with text fields, always create a `{table}_translations`
 companion table and use LEFT JOIN COALESCE in all read queries.
+
+## Naming
+
+**No abbreviated variable names.** Variables must use full descriptive names.
+Single- or two-letter names are only allowed when the abbreviation *is* the full description
+(e.g., a loop index `i`, a matrix coordinate `x`).
+
+### Examples
+
+| Avoid | Use instead |
+|-------|-------------|
+| `err` | `parseError`, `writeError`, `dbError`, `validationError` |
+| `ctx` | `requestContext`, `handlerContext`, `queryContext` |
+| `s`   | `service`, `server` |
+| `r`   | `request`, `repository` |
+| `w`   | `writer`, `responseWriter` |
+| `h`   | `handler` |
+| `req` | `request` |
+| `res` | `response`, `result` |
+| `msg` | `message` |
+| `cfg` | `config` |
+| `db`  | `database` |
+| `tx`  | `transaction` |
+| `buf` | `buffer` |
+| `tmp` | `temp`, or a descriptive name |
+
+This rule applies to all languages in this repo (Go and Dart).
+In Go, name variables to avoid shadowing the `error` built-in and the `context` package —
+use descriptive prefixes: `parseError`, `requestContext`, etc.