What changed
Google Antigravity 2.15 lets custom agents disable the IDE's default prompt sections and tools, then add back only the capabilities they need. The selected agent persists after reload, and the release also adds keyboard navigation and repairs state, permission, project-isolation and command-status failures.
Why it matters
A subtractive tool configuration can make least-privilege agents easier to define, while the isolation fixes address cases where unrelated project files or duplicate permissions entered a conversation. Both the configured surface and the enforcement path need verification.
What to do
Create a disposable custom agent with every default prompt and tool disabled, add one read-only tool, reload the IDE and test one allowed and denied action. Then open a no-folder conversation beside two projects and verify files, settings, killed commands and audit history remain isolated and correctly labeled.
Caveat
Google says Antigravity versions roll out gradually and provides no independent security or reliability evaluation. Disabling a visible default tool does not by itself prove that every indirect capability, inherited permission or connected server is unavailable.