feat(#2096): migrate Antigravity onto EoS declarative adapter + permission-writer + MCP companion (ADR-1239)
Fold all antigravity literal branches into descriptor-driven reads:
getConfigDirFromHome (→ configHome.kind 'dot-home-nested'), projectLocalHookPrefix
(→ hostBehaviors.hookPathStyle 'raw'), applyAgentPathRewrites (→ noPathRewrite),
getProjectInstructionFile (→ projectInstructionFile 'GEMINI.md'); removed the dead
inline convertClaudeAgentToAntigravityAgent branch + dead isAntigravity
destructures (antigravity is already on the descriptor-agents path). subagentToolkit
flipped undocumented→full (Context7: antigravity.google/docs/cli/features);
namedDispatch/nested/maxDepth/backgroundDispatch stay undocumented. Byte-identical
golden parity for all 16 runtimes.
UPGRADE 1 (permission-writer): permissionWriter 'antigravity' + configureAntigravityPermissions
merges a scoped permissions.allow block (GSD's own tree + hooks) into Antigravity's
settings.json — non-destructive, idempotent, symmetric uninstall. Added to
VALID_PERMISSION_WRITERS + the FinishPermissionWriter union.
UPGRADE 2 (MCP companion): configureAntigravityMcpConfig writes mcp_config.json
registering the gsd-core companion MCP server (Gemini-successor mcpServers schema,
best-effort — raw schema unpublished). Both writers dispatch from finishInstall.
settings.json is golden-excluded (HOOK_CONFIG_FILES); mcp_config.json (portable,
no absolute paths) is golden-tracked → only antigravity.json changes.
Tests: declarative-reference-antigravity extended (source-grep guard across 4
modules, fail-closed for the 4 undocumented sub-axes, validator acceptance) +
antigravity-upgrades (permission-writer + mcp_config live-install, idempotency,
user-preservation). Matrix + ADR-1016 + capability-manifest + CONTEXT.md +
connect-gsd-mcp-server docs updated; changeset (Changed).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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