[Bug]: Antigravity picker keeps the pre-update model list until a session starts, so the models from #26876 stay hidden #29073

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/server

Steps to reproduce

1. Use Antigravity on a T3 build from before 4432fbef71 (feat(antigravity): Claude and GPT models, thinking levels, and diff edits #26876). The model picker lists Gemini 3.8 Flash High / Medium / Low.
2. Update T3 to a build that includes feat(antigravity): Claude and GPT models, thinking levels, and diff edits #26876. Here: 0.1.7-nightly.20261102.4061, with the managed Antigravity ACP server 1.4.1 (installed 2026-10-30).
3. Open the model picker without starting a new Antigravity session.

Expected behavior

After the update, the picker offers the models #26876 added (Claude Sonnet 4.6, Claude Opus 4.6, GPT-OSS 120B). If the list can only refresh when a session starts, the picker says so.

Actual behavior

The picker still listed only gemini-3.8-flash-high, -medium and -low, the model list cached from my last Antigravity run on 2026-10-28. Provider checks kept updating checkedAt but not the models.

After I sent one message in a new Antigravity thread, the list changed right away to gemini-3.8-flash, claude-sonnet-4-6, claude-opus-4-6-thinking and gpt-oss-120b-medium.

Diagnosis

The health check intentionally doesn't start the agent: the comment in AntigravityDriver.ts notes it unpacks about 1 GB per launch. The model list is replaced only in onSessionStarted and onConfigOptionsUpdated, and otherwise the previous snapshot is kept. So a list from an older T3 build or agent version stays in the picker until the user happens to start a session. Someone who only sees Gemini models has no reason to do that to find the others. #13956 asked for these models and was closed as covered by 4432fbef71, but on an upgraded install they stay out of view.

To confirm the agent offered them before any T3 session, I launched the managed agy_acp_server.par 1.4.1 directly, the way T3 does (clientInfo name zed). session/new listed the Claude and GPT-OSS models.

Possible directions, for whoever picks this up: refresh the model list once when the T3 version or the managed agent version changes, or mark the list as possibly stale until a session starts.

Impact

Minor bug or occasional failure

Version or commit

0.1.7-nightly.20261102.4061

Environment

Linux, desktop AppImage, Antigravity ACP server 1.4.1 (managed), Google personal sign-in.

Workaround

Send one message in any Antigravity thread. The picker then shows the current models.