fix: do not omitempty ReadOnlyHint in ToolAnnotations

docs/rough_edges.md

@@ -63,3 +63,8 @@ v2.
 - `StreamableHTTPOptions.CrossOriginProtection` should not have been part of
   the SDK API. Cross-origin protection is a general HTTP concern, not specific
   to MCP, and can be applied as standard HTTP middleware.
+
+- `ToolAnnotations` (`mcp/protocol.go`) should have all fields typed as `*bool`
+  for full control to define what is being sent over the wire. Different
+  MCP clients have different requirements, and some of them require all fields
+  to be explicitly set to either `true` or `false`.

internal/docs/rough_edges.src.md

@@ -62,3 +62,8 @@ v2.
 - `StreamableHTTPOptions.CrossOriginProtection` should not have been part of
   the SDK API. Cross-origin protection is a general HTTP concern, not specific
   to MCP, and can be applied as standard HTTP middleware.
+
+- `ToolAnnotations` (`mcp/protocol.go`) should have all fields typed as `*bool`
+  for full control to define what is being sent over the wire. Different
+  MCP clients have different requirements, and some of them require all fields
+  to be explicitly set to either `true` or `false`.

mcp/protocol.go

@@ -1368,7 +1368,7 @@ type ToolAnnotations struct {
 	// (This property is meaningful only when ReadOnlyHint == false.)
 	//
 	// Default: false
-	IdempotentHint bool `json:"idempotentHint,omitempty"`
+	IdempotentHint bool `json:"idempotentHint"`
 	// If true, this tool may interact with an "open world" of external entities. If
 	// false, the tool's domain of interaction is closed. For example, the world of
 	// a web search tool is open, whereas that of a memory tool is not.
@@ -1378,7 +1378,7 @@ type ToolAnnotations struct {
 	// If true, the tool does not modify its environment.
 	//
 	// Default: false
-	ReadOnlyHint bool `json:"readOnlyHint,omitempty"`
+	ReadOnlyHint bool `json:"readOnlyHint"`
 	// A human-readable title for the tool.
 	Title string `json:"title,omitempty"`
 }