Agent Teams: Per-teammate model selection

[ivbrajkovic]

Hi team 👋 — per CONTRIBUTING.md I'm bringing this here as an Ideas discussion, since external pull requests aren't accepted at the moment.

Problem

In Agent Teams, every teammate inherits the Lead's model. There is no way to route individual teammates to different providers/models (a cheap reviewer next to a strong implementer, for example), even though the one-shot subagent tool already supports per-delegation selection through the subagent-model-selection setting.

Proposal

Let spawn_teammate accept optional provider, model, and reasoning_effort with the same semantics as the subagent tool:

• Omitted values inherit the Lead's route at creation time.
• Selection is gated by the same Host subagent-model-selection user setting and the same per-session route allowlist, so one toggle governs both delegation surfaces and no new user-facing configuration is needed.
• list_subagent_models serves route discovery for Team members as well.
• The durable roster row records the teammate's resolved model, so list_agents shows each member's actual model.

The continuation seam already supports this: startContinuable accepts agentOptions, persists the resolved route in the child's own subagent descriptor, and restores it on cold resume — so no new durability machinery is required.

One finding that may matter independently

While testing the shipped web composition (standard preset + Agent Teams bundle enabled), both selection surfaces registered list_subagent_models into the same agent scope, and new session creation failed with tool "list_subagent_models" is already registered in this scope. The web preset's nested tool-subagent row (with modelSelectionSettings: true) coexists with the Agent Teams bundle, whose disables only cover top-level rows. The implementation fixes this with a reference-counted, per-scope shared registration, so a composition mounting both surfaces presents exactly one discovery definition.

Status

A complete implementation is running and tested locally (based on master at 639ed01539, i.e. 0.2.0-rc.2) and pushed to my fork: feat/agent-team-teammate-model-selection — four commits: shared model-selection machinery, service-level route pass-through, the spawn_teammate surface, and docs/records.

• Unit tests for every changed path with 100% per-file coverage on the touched src files; full repository typecheck, lint, and doc gates pass.
• The keyless team-targets snapshot is updated; bilingual package READMEs, subsystem docs, and the team/member persistence-type acknowledgement follow the repo's own policy files.
• Live-verified in the web app: Lead on deepseek-official/deepseek-flash, teammate spawned with zai/glm-5.3-flash + low effort — the teammate runs and replies on the selected route, and list_agents reports both models.

Offer

Happy to share the patch, walk through the design, or rebase onto whatever base the team prefers — and equally fine if you would rather implement it internally; the design notes and the registration-collision finding above are the main takeaways. Thanks for a great harness!