⚡ Bolt: Optimize common passwords parsing with zero-allocation line iteration

.jules/bolt.md

@@ -20,3 +20,7 @@
 ## 2026-05-27 - Reducing Allocations with bufio.Scanner
 **Learning:** Parsing large embedded strings (like blocklists) using `strings.Split` creates a large slice of strings that persists until the loop finishes. This is inefficient for one-time map population.
 **Action:** Use `bufio.Scanner` with `strings.NewReader` to process the string line-by-line. This minimizes temporary allocations and is significantly more memory-efficient for large text datasets.
+
+## 2026-06-05 - Optimizing string parsing
+**Learning:** Using bufio.Scanner for parsing strings in memory still requires allocating scanner structures and copying slices. A loop matching on newlines (`strings.IndexByte`) and slicing directly from the original string is significantly faster and requires zero extra allocations.
+**Action:** Use index-based slicing instead of bufio.Scanner when extracting lines from embedded strings that are only parsed once.

internal/core/passwords.go

@@ -1,7 +1,6 @@
 package core
 
 import (
-	"bufio"
 	_ "embed"
 	"strings"
 	"sync"
@@ -18,10 +17,16 @@ var (
 
 func parseCommonPasswords() {
 	commonPasswords = make(map[string]struct{})
-	scanner := bufio.NewScanner(strings.NewReader(commonPasswordsRaw))
-	for scanner.Scan() {
-		p := strings.TrimSpace(scanner.Text())
-		if p == "" || strings.HasPrefix(p, "#") {
+	s := commonPasswordsRaw
+	for len(s) > 0 {
+		var line string
+		if i := strings.IndexByte(s, '\n'); i >= 0 {
+			line, s = s[:i], s[i+1:]
+		} else {
+			line, s = s, ""
+		}
+		p := strings.TrimSpace(line)
+		if p == "" || p[0] == '#' {
 			continue
 		}
 		commonPasswords[strings.ToLower(p)] = struct{}{}