[Bug]: Missing ACP runtime is reported as Antigravity itself not installed#25433

Before submitting

• I searched existing issues and did not find an open report for this specific diagnostic.
• I included enough detail to reproduce or investigate the problem.

Area

apps/server

Steps to reproduce

1. Have the Antigravity app or agy CLI installed, without T3 Code's separate Antigravity ACP runtime.
2. Open Settings > Providers and enable Antigravity.
3. Let the provider status check finish.

Expected behavior

Explain that the ACP agent runtime required by T3 Code is missing and needs its own installation. The message should distinguish it from the Antigravity app, IDE, and CLI.

Actual behavior

The provider says:

Antigravity is not installed. Install it in this environment or set a custom executable path.

I had Antigravity.app 2.26.0, Antigravity IDE 2.5.5, and agy --version reporting 1.3.2. The message made this look like failed app detection.

Source investigation shows the resolver intentionally looks for a managed ACP runtime, or agy_acp_server.par with an executable localharness_external sibling. It does not use the installed app or CLI. The installation behavior is correct; the diagnostic does not explain what is missing.

Impact

Minor bug or occasional failure: misleading setup guidance.

Version or commit

Desktop 0.1.2; the diagnostic is still present on main at 1316d48b0c68.

Environment

macOS 27.2, Apple Silicon (arm64).

Workaround

Used Install Antigravity in T3 Code's provider settings and completed the separate Google sign-in. T3 then showed ACP runtime v1.3.0 authenticated with six models available. No app reinstall or PATH changes were needed.

Related reports

• #12067 was answered and closed: the separate ACP installation is intentional.
• #10932 previously addressed this wording and was closed during the V2 rewrite. A maintainer invited a fresh PR once V2 landed.
• #14303 and #23746 cover setup discoverability and the initially disabled Install action. This report is limited to the completed missing-runtime diagnostic, not loading state or installation behavior.

Investigated with GPT-6 in Codex.