Enhancement: Configurable Maximum Agent Recursion Depth

Currently, agent recursion depth is hard-coded to a limit of 1 (primary agent can spawn sub-agents, but sub-agents cannot spawn further). This proposal suggests exposing this limit as a configurable setting in config.toml (e.g., agents.max_depth).

Motivation
Advanced orchestration workflows and hierarchical agent structures often require nesting deeper
than a single level. Hard-coding this limit restricts the tool's flexibility for power users
who are already building complex multi-agent systems.

By making this configurable:

1. Flexibility: Advanced users can opt-in to deeper recursion (e.g., depth 4) to support

complex task decomposition.

1. Safety: The default can remain at 1 to prevent runaway costs or loops for standard users.
2. Consistency: It aligns with other "knobs" in Codex that allow users to tune the engine to

their specific environment.

Proposed Implementation

• Add a max_depth field to the [agents] section of the configuration.
• Update the recursion guard in the Rust core to check against this configured value instead

of a static constant.

• Ensure the setting is propagated through the tool invocation context.

I have already implemented a working prototype of this change and am happy to submit a PR for
review.