fix(core): stream Code Mode tool progress - #38718

Summary

• publish nested Code Mode tool start, child progress, and settlement metadata live
• serialize call-state updates with progress publication for parallel executions
• mark running child calls failed when execute is interrupted

Testing

• bun typecheck in packages/core
• focused execute and ToolRegistry tests: 24 passed
• full Core suite: 1,436 passed; one unrelated npm timeout passed on isolated rerun
• Prettier and git diff --check