MCP Tools: change []string to *[]string to preserve nil vs empty

With `json:"tools,omitempty"` on a bare []string, Go collapses both
nil and []string{} to "omitted", losing the documented distinction
between "all tools" (nil) and "no tools" (empty slice). Switch the
field type to *[]string so a non-nil pointer to an empty slice
serializes as `tools: []` on the wire, matching TS `tools?: string[]`
and C# `IList<string>?` with WhenWritingNull.

Callers use the standard Go idiom for pointer-to-slice literals:
  Tools: &[]string{"*"}       // explicit all tools
  Tools: &[]string{}          // no tools
  Tools: &[]string{"a","b"}   // only those tools
  Tools: nil                  // (default) all tools, field omitted

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SteveSandersonMS

docs/features/mcp.md

@@ -120,7 +120,7 @@ func main() {
             "my-local-server": copilot.MCPStdioServerConfig{
                 Command: "node",
                 Args:    []string{"./mcp-server.js"},
-                Tools:   []string{"*"},
+                Tools:   &[]string{"*"},
             },
         },
     })

go/internal/e2e/mcp_and_agents_e2e_test.go

@@ -21,7 +21,7 @@ func TestMCPServersE2E(t *testing.T) {
 			"test-server": copilot.MCPStdioServerConfig{
 				Command: "echo",
 				Args:    []string{"hello"},
-				Tools:   []string{"*"},
+				Tools:   &[]string{"*"},
 			},
 		}
 
@@ -63,7 +63,7 @@ func TestMCPServersE2E(t *testing.T) {
 		mcpServers := map[string]copilot.MCPServerConfig{
 			"test-server": copilot.MCPStdioServerConfig{
 				Command: "echo",
-				Tools:   []string{"*"},
+				Tools:   &[]string{"*"},
 			},
 		}
 
@@ -118,7 +118,7 @@ func TestMCPServersE2E(t *testing.T) {
 			"test-server": copilot.MCPStdioServerConfig{
 				Command: "echo",
 				Args:    []string{"hello"},
-				Tools:   []string{"*"},
+				Tools:   &[]string{"*"},
 			},
 		}
 
@@ -159,7 +159,7 @@ func TestMCPServersE2E(t *testing.T) {
 			"env-echo": copilot.MCPStdioServerConfig{
 				Command: "node",
 				Args:    []string{mcpServerPath},
-				Tools:   []string{"*"},
+				Tools:   &[]string{"*"},
 				Env:     map[string]string{"TEST_SECRET": "hunter2"},
 				Cwd:     mcpServerDir,
 			},
@@ -198,12 +198,12 @@ func TestMCPServersE2E(t *testing.T) {
 			"server1": copilot.MCPStdioServerConfig{
 				Command: "echo",
 				Args:    []string{"server1"},
-				Tools:   []string{"*"},
+				Tools:   &[]string{"*"},
 			},
 			"server2": copilot.MCPStdioServerConfig{
 				Command: "echo",
 				Args:    []string{"server2"},
-				Tools:   []string{"*"},
+				Tools:   &[]string{"*"},
 			},
 		}
 
@@ -366,7 +366,7 @@ func TestCustomAgentsE2E(t *testing.T) {
 					"agent-server": copilot.MCPStdioServerConfig{
 						Command: "echo",
 						Args:    []string{"agent-mcp"},
-						Tools:   []string{"*"},
+						Tools:   &[]string{"*"},
 					},
 				},
 			},
@@ -437,7 +437,7 @@ func TestCombinedConfigurationE2E(t *testing.T) {
 			"shared-server": copilot.MCPStdioServerConfig{
 				Command: "echo",
 				Args:    []string{"shared"},
-				Tools:   []string{"*"},
+				Tools:   &[]string{"*"},
 			},
 		}
 

go/internal/e2e/rpc_mcp_and_skills_e2e_test.go

@@ -112,7 +112,7 @@ func TestRpcMcpAndSkillsE2E(t *testing.T) {
 				serverName: copilot.MCPStdioServerConfig{
 					Command: "echo",
 					Args:    []string{"rpc-list-mcp-server"},
-					Tools:   []string{"*"},
+					Tools:   &[]string{"*"},
 				},
 			},
 		})

go/types.go

@@ -650,11 +650,15 @@ type MCPServerConfig interface {
 //
 // The Tools field controls which tools from the server are exposed:
 //   - nil (omitted from the wire): all tools (CLI default)
-//   - []string{"*"}: explicit "all tools"
-//   - []string{}: no tools
-//   - []string{"foo","bar"}: only those tools
+//   - &[]string{"*"}: explicit "all tools"
+//   - &[]string{}: no tools
+//   - &[]string{"foo","bar"}: only those tools
+//
+// The pointer-to-slice form is required to distinguish "omitted" (all tools)
+// from "empty list" (no tools) on the wire, matching TypeScript's
+// `tools?: string[]` and C#'s `IList<string>?` semantics.
 type MCPStdioServerConfig struct {
-	Tools   []string          `json:"tools,omitempty"`
+	Tools   *[]string         `json:"tools,omitempty"`
 	Timeout int               `json:"timeout,omitempty"`
 	Command string            `json:"command"`
 	Args    []string          `json:"args,omitempty"`
@@ -680,7 +684,7 @@ func (c MCPStdioServerConfig) MarshalJSON() ([]byte, error) {
 //
 // See [MCPStdioServerConfig] for the semantics of the Tools field.
 type MCPHTTPServerConfig struct {
-	Tools   []string          `json:"tools,omitempty"`
+	Tools   *[]string         `json:"tools,omitempty"`
 	Timeout int               `json:"timeout,omitempty"`
 	URL     string            `json:"url"`
 	Headers map[string]string `json:"headers,omitempty"`

test/scenarios/tools/mcp-servers/go/main.go

@@ -33,7 +33,7 @@ func main() {
 		mcpServers["example"] = copilot.MCPStdioServerConfig{
 			Command: cmd,
 			Args:    args,
-			Tools:   []string{"*"},
+			Tools:   &[]string{"*"},
 		}
 	}