agent: centralize session and node registry resets

src/agent/Agent.zig

@@ -878,6 +878,12 @@ fn attemptSelfHeal(self: *Self, arena: std.mem.Allocator, failed_command: []cons
     return null;
 }
 
+/// Tear down the browser session and start fresh. Used by the MCP `task` tool
+/// when the caller asks for an isolated run.
+pub fn resetSession(self: *Self) !void {
+    return self.tool_executor.resetSession();
+}
+
 /// MCP entry point: run a single user task with a clean LLM context. Browser
 /// state (URL, cookies, etc.) is preserved by default; pass a fresh session
 /// upstream if isolation is needed. Returns the assistant text on success
@@ -892,7 +898,7 @@ pub fn runOneTask(
     _ = self.message_arena.reset(.retain_capacity);
     // Each task gets a fresh LLM context; drop registry entries that point
     // into the old session so a stray backendNodeId can't survive a navigation.
-    self.tool_executor.node_registry.reset();
+    self.tool_executor.resetNodeRegistry();
     self.one_shot_attachments = attachments;
     return self.processUserMessage(task, null);
 }

src/agent/McpServer.zig

@@ -111,7 +111,7 @@ pub fn handleToolCall(self: *Self, arena: std.mem.Allocator, req: protocol.Reque
     }
 
     if (args.fresh orelse false) {
-        self.agent.tool_executor.resetSession() catch |err| {
+        self.agent.resetSession() catch |err| {
             log.err(.mcp, "fresh session reset failed", .{ .err = err });
             return self.sendErrorResult(id, "Failed to start a fresh browser session");
         };

src/agent/ToolExecutor.zig

@@ -49,12 +49,17 @@ pub fn deinit(self: *Self) void {
 }
 
 /// Tear down the current `Browser` and `Session` and replace them with
-/// fresh ones. Caller is responsible for clearing any registry/cache
-/// state that depended on the old session.
+/// fresh ones. Also clears the node registry, since backendNodeIds from
+/// the old session would dangle into the new one.
 pub fn resetSession(self: *Self) !void {
     self.browser.deinit();
     try self.browser.init(self.app, .{}, null);
     self.session = try self.browser.newSession(self.notification);
+    self.node_registry.reset();
+}
+
+pub fn resetNodeRegistry(self: *Self) void {
+    self.node_registry.reset();
 }
 
 pub const CallError = browser_tools.ToolError || error{InvalidJsonArguments};