fix(agents): retry empty structured tool names (#410)

* fix(agents): retry empty structured tool names

* fix(agents): separate empty tool retry handling

* test(web): harden onboarding LLM step helper

* fix(agents): preserve empty tool retry context

* fix(agents): preserve valid sibling tool calls

* test(web): wait for chat clear in websocket e2e

* fix(agents): preserve empty tool retry context after merge

Author: penso