Clarify agent.create selector naming

[cbusillo]

Objective

Clean up the public agent.create.models naming so Every Code does not teach agents that every selectable helper is a model. Some entries, such as antigravity, are agent/CLI selectors that launch an external tool and use that tool's configured model.

Finish Line

The agent tool API, prompts, docs, and UI expose a clear selector concept without breaking existing callers that still send models.

Current Status

State: Waiting
Next action: Design a non-breaking transition, likely by adding an agents or selectors alias while keeping models as backward-compatible input.
Blocked by: None
Waiting for: The broader product-identity work in #85 to set the repo language before doing more API naming churn.
Last verified: 2026-05-23 after #98 merged Antigravity as an agent selector.

Scope

• In: agent.create tool schema, prompt examples, Auto Drive agent guidance, docs, tests, and backward-compatible request parsing.
• Out: Removing support for the existing models field in the first pass; changing external CLI model-selection behavior.

Acceptance Criteria

• A new clearer field name is chosen, such as agents or selectors.
• Existing models requests continue to work with no behavior change.
• LLM-facing descriptions explain that selectors may be model-backed Code/Claude entries or external CLI agents like antigravity.
• Docs and tests cover mixed selector lists such as code-gpt-5.4, claude-sonnet-4.6, and antigravity.
• Deprecation or compatibility behavior is documented if models remains accepted.

Relationships

Related: #85, #48, #97, #98

Validation

Run focused code-core tests for agent request parsing/schema behavior, TUI tests for Auto Drive agent guidance if touched, and ./build-fast.sh before merge.

Decisions

• Do not treat antigravity as a model slug; it is an Every Code selector that launches agy.
• Prefer a non-breaking migration over renaming the field in place.

Open Questions

• Should the canonical field be agents, selectors, or models plus a clearer description only?
• Should the TUI surface use “Agents” while the low-level API uses “selectors”?