Follow up on #64077 by using first-class ACP tool-call names while
continuing to accept legacy `_meta.tool_name` from older agents.

- Prefer the first-class name when creating a tool call. Explicit name
updates replace the stored name; legacy metadata only fills an absent
name and cannot overwrite a canonical name.
- Emit first-class names from the native agent, including replay when a
tool implementation is unavailable.

Release Notes:

- N/A