Define grain traffic policy with ManagedCode.Orleans.Graph

[KSemenenko]

Problem

The embedded host needs explicit grain-to-grain traffic policy before the session model grows into a fleet runtime.

Scope

• Define the allowed grain transitions for session, workspace, fleet, policy, and artifact grains
• Track where Orleans.Graph should enforce and visualize the policy
• Keep deadlock and reentrancy considerations visible

Out of scope

• General Orleans coding standards outside grain traffic policy
• Provider adapter implementation details

Implementation notes

• Use Orleans.Graph to make runtime boundaries explicit instead of tribal knowledge
• Keep the policy maintainable as more grains are added later
• Ensure the issue describes both configured policy and runtime visibility needs

Definition of Done

• The planned grain graph is explicit enough to implement and test later
• Future Orleans integration tests know which transitions are allowed and denied

Verification

• Review the issue against the planned grain list from the embedded-host issue

Dependencies

• Parent epic: [Epic] Add the embedded agent runtime host to the Uno desktop app #12
• Depends on: Embed an Orleans silo in the Uno desktop host and register the core grains