Allow dot in usernames per NIP-05 local-part spec

Extend usernameRE to [a-z0-9_.-], preserve dots in SanitizeForUsername,
and add tests for validation, sanitization, and nip05 sync precedence.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/user/model.go

@@ -42,8 +42,9 @@ var (
 	ErrUsernameTaken   = errors.New("username taken")
 )
 
-// Username rules: 1-30 chars, [a-z0-9_-], lowercase, must start with alnum.
+// Username rules: 1-30 chars, [a-z0-9_.-], lowercase, must start with alnum.
-var usernameRE = regexp.MustCompile(`^[a-z0-9][a-z0-9_-]{0,29}$`)
+// Dot is allowed per NIP-05 local-part spec.
+var usernameRE = regexp.MustCompile(`^[a-z0-9][a-z0-9_.-]{0,29}$`)
 
 func ValidateUsername(name string, reserved []string) error {
 	name = strings.ToLower(strings.TrimSpace(name))

internal/user/model_test.go

@@ -10,9 +10,12 @@ func TestValidateUsername(t *testing.T) {
 		{"alice", true},
 		{"al-ice_42", true},
 		{"a", true},
+		{"alice.bob", true},
+		{"alice.smith.42", true},
 		{"", false},
 		{"-alice", false},
 		{"_alice", false},
+		{".alice", false},
 		{"thisusernameiswaytoolongtobevalid12345", false},
 		{"admin", false},
 	}

internal/user/nostr_sync.go

@@ -5,7 +5,7 @@ import (
 )
 
 // SanitizeForUsername coerces an arbitrary profile string into a candidate
-// that matches usernameRE: lowercase ASCII alphanumerics, `_`, and `-`,
+// that matches usernameRE: lowercase ASCII alphanumerics, `_`, `-`, and `.`,
 // length <= 30, with an alphanumeric first character. Returns "" when no
 // usable handle can be derived.
 func SanitizeForUsername(s string) string {
@@ -22,7 +22,7 @@ func SanitizeForUsername(s string) string {
 		case (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9'):
 			b.WriteRune(r)
 			prevSep = false
-		case r == '-' || r == '_':
+		case r == '-' || r == '_' || r == '.':
 			if b.Len() == 0 {
 				continue
 			}
@@ -42,9 +42,9 @@ func SanitizeForUsername(s string) string {
 			prevSep = true
 		}
 	}
-	out := strings.TrimRight(b.String(), "_-")
+	out := strings.TrimRight(b.String(), "_-.")
 	if len(out) > 30 {
-		out = strings.TrimRight(out[:30], "_-")
+		out = strings.TrimRight(out[:30], "_-.")
 	}
 	return out
 }

internal/user/nostr_sync_test.go

@@ -17,6 +17,10 @@ func TestSanitizeForUsername(t *testing.T) {
 		{"alice_", "alice"},
 		{"alice--bob", "alice-bob"},
 		{"alice__bob", "alice_bob"},
+		{"alice.bob", "alice.bob"},
+		{"alice..bob", "alice.bob"},
+		{".alice", "alice"},
+		{"alice.", "alice"},
 		{"  ", ""},
 		{"", ""},
 		{"!!!", ""},
@@ -59,6 +63,11 @@ func TestCandidateFromMetadataPrecedence(t *testing.T) {
 			name:  "alice", nip05: "preferred@azzamo.net", dom: domain,
 			want: "preferred",
 		},
+		{
+			desc:  "nip05 local part with dot is preserved",
+			name:  "alice", nip05: "alice.smith@azzamo.net", dom: domain,
+			want: "alice.smith",
+		},
 		{
 			desc:  "nip05 ignored when domain differs",
 			name:  "alice", nip05: "preferred@other.example", dom: domain,