feat: MCP tool client infrastructure for agent extensibility

Add the full MCP tool pipeline enabling agents to invoke external tools
(like Brave Search) via MCP servers:

- Add ToolRequest/ToolResponse types and mcp-tool topics to @trustgraph/base
- Create McpToolService (FlowProcessor) that connects to external MCP servers
  via @modelcontextprotocol/sdk StreamableHTTP transport
- Add createMcpTool() to wire MCP tools into the agent's ReAct loop
- Implement config-driven tool registration in AgentService with backward-
  compatible fallback to hardcoded tools
- Add tool filtering by group and state (port of Python tool_filter.py)
- Register mcp-tool in gateway dispatcher and export from @trustgraph/flow
- Fix flow restart race condition: skip restart when flow definitions unchanged
- Update seed config with MCP server config and tool definitions
- Add run scripts for MCP tool service and Brave Search MCP server

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

ts/packages/base/src/processor/flow-processor.ts

@@ -22,6 +22,7 @@ export abstract class FlowProcessor extends AsyncProcessor {
   private specifications: Spec[] = [];
   private flows = new Map<string, Flow>();
   private configConsumer: BackendConsumer<ConfigPush> | null = null;
+  private lastFlowsJson = "";
 
   protected constructor(config: ProcessorConfig) {
     super(config);
@@ -76,6 +77,16 @@ export abstract class FlowProcessor extends AsyncProcessor {
       return;
     }
 
+    // Skip flow restart if the flow definitions haven't changed.
+    // This prevents disrupting in-flight requests when non-flow config
+    // sections (prompts, tools, mcp) are updated.
+    const flowsJson = JSON.stringify(flowDefs);
+    if (this.lastFlowsJson && flowsJson === this.lastFlowsJson && this.flows.size > 0) {
+      console.log(`[${this.config.id}] Flow definitions unchanged, skipping restart`);
+      return;
+    }
+    this.lastFlowsJson = flowsJson;
+
     // Stop removed flows
     for (const [name, flow] of this.flows) {
       if (!(name in flowDefs)) {

ts/packages/base/src/schema/messages.ts

@@ -304,6 +304,19 @@ export interface CollectionManagementResponse {
   collections?: { user: string; collection: string; name: string; description: string; tags: string[] }[];
 }
 
+// ---------- Tool invocation (MCP tools) ----------
+
+export interface ToolRequest {
+  name: string;
+  parameters: string; // JSON-encoded
+}
+
+export interface ToolResponse {
+  error?: TgError;
+  text?: string;    // Plain text response
+  object?: string;  // JSON-encoded structured response
+}
+
 // ---------- Flow management ----------
 
 // Flow request/response use kebab-case wire format to match the client.

ts/packages/base/src/schema/topics.ts

@@ -60,6 +60,10 @@ export const topics = {
   promptRequest: topic("prompt-request"),
   promptResponse: topic("prompt-response"),
 
+  // MCP tool invocation
+  mcpToolRequest: topic("mcp-tool-request"),
+  mcpToolResponse: topic("mcp-tool-response"),
+
   // Librarian (document management)
   librarianRequest: topic("librarian-request"),
   librarianResponse: topic("librarian-response"),