feat(providers): install Codex, Claude, and OpenCode from settings

[MatthewFeroz]

What Changed

Add individual install and update controls for Codex, Claude, and OpenCode beside the provider version in the Settings → Providers header. Their details popover contains progress, cancellation, retry, and removal, matching the existing update control location. Downloads run on the selected T3 environment and reuse Antigravity’s installation controls and background operation lifecycle.

Codex and OpenCode resolve official production releases on each explicit install/update; Claude follows its official stable channel. Antigravity retains its tested release pin and existing runtime handling. Downloaded CLIs are verified before activation, stored in T3-owned version directories, and selected through provider settings. Custom binary paths and external OpenCode servers keep their installation owner. Authentication remains separate.

Why

A missing provider currently leaves users at “Not found” and requires a separate terminal installation, including when T3 is connected to a remote environment. Individual installers let users set up the selected provider on the correct machine through the existing setup flow.

Upstream sources: OpenCode installer, Codex installer, and Claude installation documentation.

Validation

• 69 focused tests pass across provider installation, release selection, managed runtime discovery, Codex driver behavior, and shared setup controls.
• Server and web typechecks pass; targeted lint has only the existing ProviderSettingsPanel React effect warning.
• Real Codex, Claude, and OpenCode downloads, checksum checks, extraction, and version probes succeeded in an isolated macOS arm64 environment.
• Web and desktop use the same controls and environment-scoped requests. Mobile can use installed providers; its installation UI remains unchanged. Cursor and Grok are outside this change.
• Browser verification confirmed installation from the header popover, runtime removal, saved binary path, detected version, and loaded models. The placement change passed 15 focused UI tests and web typechecking. Windows/Linux execution remains untested. Updates require stopped provider sessions; removal requires disabled instances.

UI Changes

Before	After

Header installation interaction video · Installed runtime and detected version

The before screenshot is the reporter’s original image. After screenshots and recording use an isolated macOS environment with a real OpenCode download.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

The scope is one provider-installation feature, but the diff is substantial: 24 files, including the download/verification service, provider integration, shared controls, and focused tests. The size checklist remains unchecked for that reason.

Implementation: GPT-6 via Codex.