fix: align mcp mailbox and limit contracts

internal/imapclient/backend.go

@@ -19,8 +19,8 @@ import (
 )
 
 const (
-	defaultListMessagesLimit = 20
+	DefaultListMessagesLimit = 20
-	maxListMessagesLimit     = 50
+	MaxListMessagesLimit     = 50
 	imapImplicitTLSPort      = "993"
 )
 
@@ -276,10 +276,10 @@ func imapAddress(host string) string {
 
 func clampListLimit(limit int) int {
 	if limit <= 0 {
-		return defaultListMessagesLimit
+		return DefaultListMessagesLimit
 	}
-	if limit > maxListMessagesLimit {
+	if limit > MaxListMessagesLimit {
-		return maxListMessagesLimit
+		return MaxListMessagesLimit
 	}
 	return limit
 }

internal/mcpserver/server.go

@@ -15,11 +15,6 @@ import (
 
 var ErrCredentialsNotConfigured = errors.New("credentials not configured; run `email-mcp setup`")
 
-const (
-	defaultListMessagesLimit = 20
-	maxListMessagesLimit     = 50
-)
-
 type MailService interface {
 	ListMailboxes(context.Context, secretstore.Credential) ([]imapclient.Mailbox, error)
 	ListMessages(context.Context, secretstore.Credential, string, int) ([]imapclient.MessageSummary, error)
@@ -97,12 +92,13 @@ func (s Server) Tools() []Tool {
 					"mailbox": map[string]any{
 						"type":      "string",
 						"minLength": 1,
+						"pattern":   "\\S",
 					},
 					"limit": map[string]any{
 						"type":    "integer",
-						"default": defaultListMessagesLimit,
+						"default": imapclient.DefaultListMessagesLimit,
 						"minimum": 1,
-						"maximum": maxListMessagesLimit,
+						"maximum": imapclient.MaxListMessagesLimit,
 					},
 				},
 				"required":             []string{"mailbox"},
@@ -118,6 +114,7 @@ func (s Server) Tools() []Tool {
 					"mailbox": map[string]any{
 						"type":      "string",
 						"minLength": 1,
+						"pattern":   "\\S",
 					},
 					"uid": map[string]any{
 						"type":    "integer",
@@ -303,10 +300,10 @@ func validateMailbox(mailbox string) (string, error) {
 
 func normalizeListMessagesLimit(limit *int) (int, error) {
 	if limit == nil {
-		return defaultListMessagesLimit, nil
+		return imapclient.DefaultListMessagesLimit, nil
 	}
-	if *limit < 1 || *limit > maxListMessagesLimit {
+	if *limit < 1 || *limit > imapclient.MaxListMessagesLimit {
-		return 0, fmt.Errorf("limit must be between 1 and %d", maxListMessagesLimit)
+		return 0, fmt.Errorf("limit must be between 1 and %d", imapclient.MaxListMessagesLimit)
 	}
 	return *limit, nil
 }

internal/mcpserver/server_test.go

@@ -273,14 +273,21 @@ func TestServerToolsAdvertiseValidatedArgumentContracts(t *testing.T) {
 	if !ok {
 		t.Fatalf("expected limit schema, got %#v", listProps["limit"])
 	}
-	if got := limitSchema["default"]; got != float64(defaultListMessagesLimit) && got != defaultListMessagesLimit {
+	mailboxSchema, ok := listProps["mailbox"].(map[string]any)
-		t.Fatalf("expected limit default %d, got %#v", defaultListMessagesLimit, got)
+	if !ok {
+		t.Fatalf("expected mailbox schema, got %#v", listProps["mailbox"])
+	}
+	if got := mailboxSchema["pattern"]; got != "\\S" {
+		t.Fatalf("expected mailbox pattern %q, got %#v", "\\S", got)
+	}
+	if got := limitSchema["default"]; got != float64(imapclient.DefaultListMessagesLimit) && got != imapclient.DefaultListMessagesLimit {
+		t.Fatalf("expected limit default %d, got %#v", imapclient.DefaultListMessagesLimit, got)
 	}
 	if got := limitSchema["minimum"]; got != float64(1) && got != 1 {
 		t.Fatalf("expected limit minimum 1, got %#v", got)
 	}
-	if got := limitSchema["maximum"]; got != float64(maxListMessagesLimit) && got != maxListMessagesLimit {
+	if got := limitSchema["maximum"]; got != float64(imapclient.MaxListMessagesLimit) && got != imapclient.MaxListMessagesLimit {
-		t.Fatalf("expected limit maximum %d, got %#v", maxListMessagesLimit, got)
+		t.Fatalf("expected limit maximum %d, got %#v", imapclient.MaxListMessagesLimit, got)
 	}
 
 	getMessage := tools[2]
@@ -291,6 +298,13 @@ func TestServerToolsAdvertiseValidatedArgumentContracts(t *testing.T) {
 	if !ok {
 		t.Fatalf("expected get_message properties map, got %#v", getMessage.InputSchema["properties"])
 	}
+	getMailboxSchema, ok := getProps["mailbox"].(map[string]any)
+	if !ok {
+		t.Fatalf("expected get_message mailbox schema, got %#v", getProps["mailbox"])
+	}
+	if got := getMailboxSchema["pattern"]; got != "\\S" {
+		t.Fatalf("expected mailbox pattern %q, got %#v", "\\S", got)
+	}
 	uidSchema, ok := getProps["uid"].(map[string]any)
 	if !ok {
 		t.Fatalf("expected uid schema, got %#v", getProps["uid"])
@@ -357,6 +371,53 @@ func TestRunnerRunReturnsValidationErrorsForInvalidRequests(t *testing.T) {
 	}
 }
 
+func TestRunnerRunRejectsWhitespaceOnlyMailboxValues(t *testing.T) {
+	store := &storeStub{
+		credential: secretstore.Credential{
+			Host:     "imap.example.com",
+			Username: "alice",
+			Password: "secret",
+		},
+	}
+	input := bytes.NewBufferString("{\"tool\":\"list_messages\",\"arguments\":{\"mailbox\":\"   \"}}\n")
+	output := &bytes.Buffer{}
+	runner := NewRunner(New(store, serviceStub{
+		listMailboxes: func(context.Context, secretstore.Credential) ([]imapclient.Mailbox, error) {
+			t.Fatal("ListMailboxes should not be called")
+			return nil, nil
+		},
+		listMessages: func(context.Context, secretstore.Credential, string, int) ([]imapclient.MessageSummary, error) {
+			t.Fatal("ListMessages should not be called")
+			return nil, nil
+		},
+		getMessage: func(context.Context, secretstore.Credential, string, uint32) (imapclient.Message, error) {
+			t.Fatal("GetMessage should not be called")
+			return imapclient.Message{}, nil
+		},
+	}), input, output, &bytes.Buffer{})
+
+	if err := runner.Run(context.Background()); err != nil {
+		t.Fatalf("Run returned error: %v", err)
+	}
+
+	decoder := json.NewDecoder(output)
+	if err := decoder.Decode(&struct {
+		Tools []Tool `json:"tools"`
+	}{}); err != nil {
+		t.Fatalf("failed to decode manifest: %v", err)
+	}
+
+	var response struct {
+		Error string `json:"error"`
+	}
+	if err := decoder.Decode(&response); err != nil {
+		t.Fatalf("failed to decode error response: %v", err)
+	}
+	if response.Error != "mailbox is required" {
+		t.Fatalf("unexpected error: %#v", response)
+	}
+}
+
 func TestRunnerRunAppliesDefaultLimitWhenOmitted(t *testing.T) {
 	store := &storeStub{
 		credential: secretstore.Credential{
@@ -373,7 +434,7 @@ func TestRunnerRunAppliesDefaultLimitWhenOmitted(t *testing.T) {
 			return nil, nil
 		},
 		listMessages: func(_ context.Context, cred secretstore.Credential, mailbox string, limit int) ([]imapclient.MessageSummary, error) {
-			if cred.Host != "imap.example.com" || mailbox != "INBOX" || limit != defaultListMessagesLimit {
+			if cred.Host != "imap.example.com" || mailbox != "INBOX" || limit != imapclient.DefaultListMessagesLimit {
 				t.Fatalf("unexpected call: cred=%#v mailbox=%q limit=%d", cred, mailbox, limit)
 			}
 			return []imapclient.MessageSummary{{UID: 42, Subject: "hello", From: "alice@example.com"}}, nil