fix(cli): clarify edit --from help; test edit --from validation

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/cli/admin.go

@@ -91,7 +91,7 @@ func runAccount(args []string, role store.Role, out, errOut io.Writer) int {
 		smtpSec := fs.String("smtp-security", "", "tls|starttls")
 		user := fs.String("username", "", "login username")
 		pass := fs.String("password", "", "login password (blank keeps existing)")
-		from := fs.String("from", "", "send-as address (blank keeps existing)")
+		from := fs.String("from", "", "send-as address (empty reverts to username)")
 		subj := fs.String("subject-regex", "", "inbound subject filter")
 		if err := fs.Parse(rest); err != nil {
 			return 2

internal/cli/admin_test.go

@@ -132,3 +132,17 @@ func TestAuditListCoreRenders(t *testing.T) {
 	}
 }
 
+func TestAccountEditFromValidationRejectsMailformed(t *testing.T) {
+	adminEnv(t)
+	// Seed an account so the failure is from --from validation, not a missing account.
+	run(t, "account", "add", "--name", "valacc", "--imap-host", "imap.x.com", "--username", "u@x.com")
+	// A malformed --from value must be rejected with exit code 2 before touching the account.
+	code, _, errStr := run(t, "account", "edit", "--name", "valacc", "--from", "not an address")
+	if code != 2 {
+		t.Fatalf("expected exit code 2 for malformed --from, got %d (stderr: %q)", code, errStr)
+	}
+	if errStr == "" {
+		t.Fatal("expected an error message on stderr for malformed --from, got none")
+	}
+}
+