2026-09-20 AGY Permissions for MCP and Non-Workspace Access

What I set out to do

Resolve recurring permission prompts in Antigravity CLI (agy) when invoking MCP tools and accessing files across workspace boundaries.

Diagnosed why agy was prompting for permissions:
- Antigravity defaults unconfigured MCP tools to ask, and coding-agents.nix only populated command(*) in allow.
- Non-workspace access was disabled by default (allowNonWorkspaceAccess = false), prompting on file access outside the git root.
Updated nix/home-manager/modules/coding-agents/agy/agy.nix:
- Configured allowNonWorkspaceAccess = true; in programs.antigravity-cli.settings.
Updated nix/home-manager/modules/coding-agents/common/coding-agents.nix:
- Added lib.optional cfg.enableMcp "mcp(*)" to programs.antigravity-cli.permissions.allow.
- Generalized toAgyPattern to check for existing parentheses so arbitrary tool patterns are not wrapped into command(...).
Updated nix/tests/coding-agents-contract.nix:
- Added assertions ensuring mcp(*) is in allow and allowNonWorkspaceAccess is true for antigravity-cli.
Verified formatting and test contracts using just check.
Applied changes via hm switch and committed as 0a82907 (feat(agy): allow mcp tools and non-workspace access).

Antigravity’s permission evaluator treats allowNonWorkspaceAccess as an explicit settings key at the top level of settings.json, while tool authorizations follow the action(target) DSL in permissions.allow.