GHSA-9rjw-3gwp-f59v: Coder's workspace app upsert allows cross-workspace agent rebinding via user-controlled app ID

A vulnerability in Coder's workspace app system allows attackers with template authorship or external provisioner access to redirect another user's app traffic to their own workspace. The flaw occurs because the system doesn't properly verify that an app ID belongs to the correct workspace before rebinding it to a different agent (the component that handles connections). App IDs are publicly discoverable, making this attack feasible for privileged users.