Antigravity backend

[toanalien]

Summary

Adds Google Antigravity CLI (agy) as a first-class Jean chat backend with streaming responses, tool-call rendering, conversation resume, model discovery, managed installation, settings, onboarding, and MCP integration.

The implementation was validated against the real agy 1.1.9 CLI. During live testing, the stream parser, model IDs, execution flags, backend routing, and response persistence were corrected to match actual runtime behavior.

What changed

Backend and execution

• Adds Backend::Antigravity and persists antigravity_session_id across sessions and runs.
• Executes agy in headless streaming mode with --output-format stream-json.
• Parses real agy events (init, step_update, and result) for incremental text, tool calls, usage, and conversation IDs.
• Resumes subsequent turns with --conversation <id>.
• Uses native Antigravity execution modes (--mode plan / --mode accept-edits).
• Normalizes Jean model IDs by removing the internal antigravity/ prefix before invoking agy.
• Clamps Jean effort levels to the values supported by agy: low, medium, and high.
• Persists completed Antigravity responses into Jean run JSONL so chat history survives navigation and restart.

CLI integration

• Detects agy from PATH and supports Jean-managed installation/uninstallation.
• Discovers available models from agy models with tested fallback models.
• Detects the local Antigravity authentication state.
• Automatically trusts the active workspace for non-interactive execution.
• Removes inherited ANTIGRAVITY_* environment variables before spawning the CLI.
• Synchronizes Jean's managed MCP server with ~/.gemini/config/mcp_config.json.

UI and preferences

• Adds Antigravity to the backend and model pickers.
• Adds an Antigravity preferences pane with installation, version, and authentication status.
• Adds Antigravity to onboarding and the new-session flow.
• Adds Antigravity support to Magic Prompt backend selection.
• Uses the official Google Antigravity logo.

Runtime verification

Verified locally with agy 1.1.9:

• Real stream-json text events are rendered incrementally.
• Tool events and tool output are parsed.
• gemini-3.6-flash-high and other IDs returned by agy models are accepted.
• A second turn resumes the first conversation using the captured conversation ID.
• --json-schema returns top-level structured_output for one-shot operations.
• MCP configuration path and shape match Antigravity's built-in documentation.
• The official installer URL returns HTTP 200.
• Completed responses remain visible after session reload.

Validation

• bun run typecheck
• bun run lint
• cargo check --manifest-path jean-core/Cargo.toml
• cargo check --manifest-path src-tauri/Cargo.toml --no-default-features
• Antigravity Rust tests, including fixtures captured from real agy output
• Manual end-to-end test through Jean Dev using the real agy binary

How to test

terminal 1

export PATH="$HOME/.bun/bin:$HOME/.local/bin:$PATH"
bun run dev

terminal 2

pkill -9 -f 'src-tauri/target/debug/jean' 2>/dev/null || true

screen -dmS jean-dev /bin/zsh -lc '
  export PATH="$HOME/.bun/bin:$HOME/.local/bin:$PATH"
  exec ./src-tauri/target/debug/jean
'

Screenshots