fix(runtime): isolate agent state by project (#101)

crates/domain/src/ids.rs

@@ -115,3 +115,34 @@ typed_id!(
     /// Identifies a first-class background task.
     TaskId
 );
+
+/// Runtime-only key for an agent scoped by its project.
+///
+/// `AgentId` is persisted inside a project and is not globally unique across
+/// simultaneously opened projects. Any app-wide in-memory registry that tracks
+/// live runtime state for an agent must use this key instead of `AgentId` alone.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct RuntimeAgentKey {
+    /// Project that owns the runtime agent.
+    pub project_id: ProjectId,
+    /// Agent inside that project.
+    pub agent_id: AgentId,
+}
+
+impl RuntimeAgentKey {
+    /// Builds a scoped runtime key from its persisted identifiers.
+    #[must_use]
+    pub const fn new(project_id: ProjectId, agent_id: AgentId) -> Self {
+        Self {
+            project_id,
+            agent_id,
+        }
+    }
+}
+
+impl std::fmt::Display for RuntimeAgentKey {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}:{}", self.project_id, self.agent_id)
+    }
+}