- extraEnv overrides agent_kinds.encrypted_env same-name keys (spec §6.1 #11)
- Prevents admin from hard-coding ACW_MCP_TOKEN in agent_kinds
- SessionService passes nil for now; system token wiring lands in I4
- BuildSpawnEnv exported for testing the override priority
- Fix app.go NewSupervisor call to match updated signature (from I5)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>