Regression test for the fix in 30cd08b (replaced
`root.parent().unwrap()` with `.unwrap_or(root.as_path())` at
main.rs:45). Two cases:
- `agent_root_slash_does_not_panic` — `AGENT_ROOT=/ assemble /dev/null`
must reach the "parse failed" error path without panicking. Guards
against the `relative_to()` call site specifically.
- `agent_root_slash_full_run_no_panic` — same env with a valid stub
manifest supplied explicitly. Even though the run fails at
`mkdir /_generated` (unprivileged), it must fail GRACEFULLY, not
with SIGABRT from an `.unwrap()` on a None parent.
Both assertions: no "panicked at" in stderr, and `status.code()` is
Some (signal-kill would return None on Unix).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
