refactor: use Wallace str_starts_with for prefix matching

Replace manual case-insensitive prefix matching with Wallace parser's
str_starts_with. Note: parameter order is reversed (string, prefix)
compared to our internal implementation (prefix, string).

Documented parameter order difference in parser-improvements.md.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: bartveneman

parser-improvements.md

@@ -3,7 +3,13 @@
 Issues and enhancement suggestions discovered during css-tree → Wallace parser migration.
 
 ## API Inconsistencies
-_(To be filled during migration)_
+
+### `str_starts_with` parameter order
+**Issue:** The parameter order for `str_starts_with(string, prefix)` is the opposite of common JavaScript conventions and our internal `startsWith(prefix, string)` function.
+
+**Impact:** When migrating from custom implementations, developers must remember to swap parameters.
+
+**Suggestion:** Consider documenting this clearly or providing an alias that matches common JS conventions where the needle comes before the haystack.
 
 ## Missing Features
 _(To be filled during migration)_

src/string-utils.ts

@@ -1,4 +1,4 @@
-import { str_equals } from '@projectwallace/css-parser'
+import { str_equals, str_starts_with } from '@projectwallace/css-parser'
 
 /**
  * Case-insensitive compare two character codes
@@ -69,17 +69,7 @@ export function endsWith(base: string, maybe: string): boolean {
  *
  * @returns true if `base` starts with `maybe`, false otherwise
  */
-export function startsWith(base: string, maybe: string) {
-	if (base === maybe) return true
-
-	let len = base.length
-	if (maybe.length < len) return false
-
-	for (let i = 0; i < len; i++) {
-		if (compareChar(base.charCodeAt(i), maybe.charCodeAt(i)) === false) {
-			return false
-		}
-	}
-
-	return true
+export function startsWith(base: string, maybe: string): boolean {
+	// Note: parameter order is swapped - Wallace's str_starts_with takes (string, prefix)
+	return str_starts_with(maybe, base)
 }