feat(FN-940): allow terminated agents to restart as active or running

- Remove blanket block on terminated→any state transitions in agent-store
- Add active and running as valid transitions from terminated state in types
- Update tests to verify terminated→active and terminated→running succeed
- Add tests for invalid terminated transitions (idle, paused) still throwing

packages/core/src/agent-store.test.ts

@@ -405,17 +405,35 @@ describe("AgentStore", () => {
       ).rejects.toThrow("Invalid state transition: idle -> terminated");
     });
 
-    it("transition from terminated to any state throws", async () => {
+    it("transition from terminated to invalid states throws", async () => {
       const agent = await createReadyAgent(store, "Terminated");
       await store.updateAgentState(agent.id, "active");
       await store.updateAgentState(agent.id, "terminated");
 
-      await expect(
-        store.updateAgentState(agent.id, "active")
-      ).rejects.toThrow("Cannot transition from terminated");
       await expect(
         store.updateAgentState(agent.id, "idle")
-      ).rejects.toThrow("Cannot transition from terminated");
+      ).rejects.toThrow("Invalid state transition: terminated -> idle");
+      await expect(
+        store.updateAgentState(agent.id, "paused")
+      ).rejects.toThrow("Invalid state transition: terminated -> paused");
+    });
+
+    it("terminated → active transition succeeds", async () => {
+      const agent = await createReadyAgent(store, "RestartActive");
+      await store.updateAgentState(agent.id, "active");
+      await store.updateAgentState(agent.id, "terminated");
+
+      const updated = await store.updateAgentState(agent.id, "active");
+      expect(updated.state).toBe("active");
+    });
+
+    it("terminated → running transition succeeds", async () => {
+      const agent = await createReadyAgent(store, "RestartRunning");
+      await store.updateAgentState(agent.id, "active");
+      await store.updateAgentState(agent.id, "terminated");
+
+      const updated = await store.updateAgentState(agent.id, "running");
+      expect(updated.state).toBe("running");
     });
 
     it("emits both 'agent:stateChanged' and 'agent:updated' events", async () => {

packages/core/src/agent-store.ts

@@ -244,10 +244,6 @@ export class AgentStore extends EventEmitter {
         return agent; // No change needed
       }
 
-      if (currentState === "terminated") {
-        throw new Error(`Cannot transition from terminated state to ${newState}`);
-      }
-
       const validTransitions = AGENT_VALID_TRANSITIONS[currentState];
       if (!validTransitions.includes(newState)) {
         throw new Error(

packages/core/src/types.ts

@@ -1292,7 +1292,7 @@ export const AGENT_VALID_TRANSITIONS: Record<AgentState, AgentState[]> = {
   running: ["active", "paused", "error", "terminated"],
   paused: ["active", "terminated"],
   error: ["active", "terminated"],
-  terminated: [], // Terminal state - no exits
+  terminated: ["active", "running"], // Can be restarted
 };
 
 /** Single heartbeat event recorded for an agent */