Document model selection for Auggie ACP in Zed (CSS-1158)

[mgmonteleone]

Problem

CSS-1158 — the model dropdown disappeared for Auggie over ACP in Zed.

Root cause is Zed-side, not Auggie-side: Zed removed the unstable ACP model selector in zed#58308 (merged 2026-06-02, first tag v1.6.0-pre), replacing it with ACP session config options. On Zed main, impl AgentConnection for AcpConnection no longer implements model_selector(), so no external ACP agent gets a model dropdown. The 0.29.0 correlation is timing: Auggie 0.29.0 published 2026-06-05, days after that Zed change.

Auggie still emits models (and modes) in session/new but emits configOptions: null, so there is nothing for current Zed to render.

Solution

This repo only ships a declarative extension.toml; it cannot change what Auggie advertises over ACP, and Zed only honors env overrides for extension-provided agent servers. So the actual fix — Auggie exposing the model as an ACP session config option — belongs in the Auggie CLI, and CSS-1158 should carry that work.

This PR documents the root cause and the two working ways to pick a model today (model in ~/.augment/settings.json, or a custom Zed agent server entry passing -m).

Testing

Verified by driving session/new over stdio against Auggie 0.16.0 / 0.28.0 / 0.29.0 / 0.36.0 / 0.37.0-prerelease.3:

• all versions return identical initialize results (protocolVersion: 1) and a populated models.availableModels (40 models) — no Auggie regression at 0.29.0;
• all versions return configOptions: null;
• auggie --acp -m claude-sonnet-4-6 yields currentModelId: "claude-sonnet-4-6", confirming the documented -m workaround.

No automated test added: the change is documentation-only and the ACP handshake requires an authenticated account.

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Pull Request opened by Augment Code | View session

[mgmonteleone]

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