pub fn resolve_shared_definitions_dir() -> Option<PathBuf>Expand description
Resolve the GLOBAL <home>/shared/agents/definitions/ directory.
Sibling of resolve_shared_registry_dir: since P0.3 both the definition
store and the instance registry are channel-independent, resolved via
the same resolve_global_shared_root so an agent created/named in one
channel is visible in every channel (cross-channel agent persistence,
P0.2/P0.3). Resolves via the launcher-exported AGENTMUX_SHARED_DIR, with
a test override and a ~/.agentmux/shared fallback.