## Why
Command arguments and environment variables can contain credentials. Logging them when spawning a child process can expose those credentials in trace output.
## What changed
Replace argument, `arg0`, and environment contents in `spawn_child_async` trace logs with argument and environment counts and a flag indicating whether `arg0` is overridden. Keep the program, working directory, network sandbox policy, and stdio policy in the trace.
## Testing
Add a regression test that captures trace output and verifies that argument, `arg0`, and environment canaries are omitted while the program path remains visible.
GitOrigin-RevId: c317e7dcc6fd8b4eafb6fcfe98dc8634807c813d
