spawn_agent's model override list is capped at five rows

What happened

spawn_agent's tool description advertises at most five model overrides, taken from the first five picker-visible rows of the model catalogue. When the catalogue comes from model_catalog_json (a custom/local provider, or any setup that merges extra models into the picker), every model past the first five is invisible in that list even though model/list and the picker return all of them.

Evidence

Client: codex-cli 0.154.0-alpha.6.2 (bundled app-server), -c model_catalog_json=<file> with a 26-row catalogue. A local sink that answers 426 to the WebSocket upgrade recorded the first /responses body, and the spawn_agent declaration inside it reads:

Available model overrides (optional; inherited parent model is preferred):
- `gpt-6-astra`: ...
- `gpt-5.6-sol`: ...
- `gpt-5.6-terra`: ...
- `gpt-5.6-luna`: ...
- `gpt-5.5`: ...

Exactly the first five rows of the catalogue, in order. Raising the catalogue to more rows does not extend the list. This matches MAX_SPAWN_AGENT_MODEL_OVERRIDES = 5 in codex-rs/core/src/tools/handlers/multi_agents_common.rs (checked against rust-v0.153.4).

Passing an id outside the list still works: find_spawn_agent_model_name searches the full model list, so a model id the user knows about is routed correctly. The cap therefore costs discoverability, not correctness - an agent that has not been told the id cannot see it exists.

Suggestion

One of:

• list every eligible model in the description,
• raise or remove MAX_SPAWN_AGENT_MODEL_OVERRIDES,
• keep the cap but emit and N more so a reader knows the list is truncated (today the text reads as if five were all there is).

Happy to test a build with any of these.

Start in codex-rs/core/src/tools/handlers/multi_agents_common.rs, inspect MAX_SPAWN_AGENT_MODEL_OVERRIDES and the code that builds the spawn_agent description from the model catalogue. Reproduce with a model_catalog_json file containing more than five rows and compare the advertised overrides with model/list and picker results. Done means the description accurately communicates the available eligible models, including how any truncation is represented.