fix(multiverse): introduce provisioning stub with its receiver

Signed-off-by: Logan Johnson <loganj@squareup.com>

desktop/src-tauri/src/managed_agents/broker_launch.rs

@@ -2,6 +2,8 @@
 //! Automatic issuance is not in the merged broker contract. Keep the production
 //! provider fail-closed until that host-owned adapter is supplied; do not mint a
 //! competing bearer token or fall back to exporting the agent key.
+use super::ManagedAgentRecord;
+use buzz_core_pkg::desktop_lifecycle::Outcome;
 use std::process::Command;
 
 pub(crate) struct LaunchScope<'a> {
@@ -106,6 +108,14 @@ impl BrokerSession {
     }
 }
 
+/// Explicit external integration gate, not a fabricated successful launch.
+pub(crate) fn provision(
+    _scope: LaunchScope<'_>,
+    _record: &ManagedAgentRecord,
+) -> Result<BrokerSession, Outcome> {
+    Err(Outcome::ProvisioningUnavailable)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;