Creates an Agent from global config (API credentials, system prompt,
identity), overrides tools with the agent's tool set, and runs through
the standard Backend → run_with_backend → Agent::turn() path.
This enables poc-hook spawned agents (surface-observe, journal, etc.)
to work with the completions API instead of the deleted chat API.
Also added Default derive to CliArgs for config loading.
Co-Authored-By: Proof of Concept <poc@bcachefs.org>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
850008ece7