## Problem
Custom agents were only installing to Claude Code (.claude/commands/)
but not to Antigravity (.agent/) or other IDEs that lack installCustomAgentLauncher function.
## Root Cause
Antigravity was missing the installCustomAgentLauncher function that the
IdeManager calls to install custom agents during agent installation.
## Solution
Added installCustomAgentLauncher function to Antigravity that:
- Creates .agent directory if needed
- Generates custom agent launchers with @agentPath references
- Uses same pattern as existing Antigravity agent launchers
- Returns proper installation result for tracking
## Result
Custom agents now install to:
- Claude Code: .claude/commands/bmad/custom/agents/ ✅
- Antigravity: .agent/bmad-custom-agents-{agentName}.md ✅
- Codex: (already working) ✅
All configured IDEs now receive custom agent installations!
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