fix(locale): handle shared calling codes for fictional numbers

For fictional numbers (no parsed region) with a "+" prefix under a
shared calling code (e.g. +1 for US/CA), use INTERNATIONAL format
to avoid misattribution. Local numbers without "+" prefix still
format as NATIONAL since the user is entering a domestic number.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: cpcloud

internal/locale/phone.go

@@ -22,17 +22,25 @@ func FormatPhoneNumber(number, regionCode string) string {
 		return number
 	}
 	// Prefer region comparison (distinguishes US/CA under shared +1 code).
-	// Fall back to country-code comparison for fictional numbers (e.g. 555-xxxx)
-	// that parse successfully but return an empty region.
 	parsedRegion := phonenumbers.GetRegionCodeForNumber(parsed)
 	if parsedRegion != "" {
 		if parsedRegion == regionCode {
 			return phonenumbers.Format(parsed, phonenumbers.NATIONAL)
 		}
 		return phonenumbers.Format(parsed, phonenumbers.INTERNATIONAL)
 	}
-	if int(parsed.GetCountryCode()) == phonenumbers.GetCountryCodeForRegion(regionCode) {
-		return phonenumbers.Format(parsed, phonenumbers.NATIONAL)
+	// Fictional numbers (e.g. 555-xxxx) parse but have no region. When
+	// the input lacks a "+" prefix, the user entered a local number — use
+	// NATIONAL if the country code matches. When "+" is present, the user
+	// explicitly typed an international code; for shared codes like +1
+	// (US/CA) use INTERNATIONAL to avoid misattribution.
+	cc := int(parsed.GetCountryCode())
+	if cc != phonenumbers.GetCountryCodeForRegion(regionCode) {
+		return phonenumbers.Format(parsed, phonenumbers.INTERNATIONAL)
+	}
+	if strings.HasPrefix(trimmed, "+") &&
+		len(phonenumbers.GetRegionCodesForCountryCode(cc)) > 1 {
+		return phonenumbers.Format(parsed, phonenumbers.INTERNATIONAL)
 	}
-	return phonenumbers.Format(parsed, phonenumbers.INTERNATIONAL)
+	return phonenumbers.Format(parsed, phonenumbers.NATIONAL)
 }

internal/locale/phone_test.go

@@ -22,7 +22,8 @@ func TestFormatPhoneNumber(t *testing.T) {
 		{"US national", "5551234567", "US", "(555) 123-4567"},
 		{"UK national", "02079460958", "GB", "020 7946 0958"},
 		{"international prefix", "+442079460958", "US", "+44 20 7946 0958"},
-		{"same-region prefix", "+15551234567", "US", "(555) 123-4567"},
+		{"same-region prefix real", "+12025551234", "US", "(202) 555-1234"},
+		{"shared-code fictional prefix", "+15551234567", "US", "+1 555-123-4567"},
 		{"already formatted", "(555) 123-4567", "US", "(555) 123-4567"},
 		{"cross-border shared code", "+16135551234", "US", "+1 613-555-1234"},
 		{"garbage passthrough", "not a phone", "US", "not a phone"},