fix: enforce one Pi runtime per user

backend/test/routes-sessions.test.ts

@@ -181,15 +181,25 @@ test("POST /sessions usa i settings (workspace/provider/model/thinking) e crea+a
   unlinkSync(modelKey);
 });
 
-test("POST /sessions reclaims a finalized runtime before enforcing the Pi limit", async () => {
+test("POST /sessions stops the user's previous open Pi runtime before creating another", async () => {
   const runtimes = new Map<string, any>();
-  const statuses = new Map<string, string>();
   const tornDown: string[] = [];
   const order: string[] = [];
   let nextId = 0;
   const app = buildApp(loadConfig({ THT_HARNESS_DIR: "../harness" }), {
     mgr: {
       get: (id: string) => runtimes.get(id),
+      teardownForPrincipal: () => {
+        const stopped: string[] = [];
+        for (const [id, runtime] of [...runtimes]) {
+          runtimes.delete(id);
+          stopped.push(id);
+          tornDown.push(id);
+          order.push(`teardown:${id}`);
+          runtime.bridge.emitClientEvent?.({ type: "system_event", event: "agent_end" });
+        }
+        return stopped;
+      },
       createFor: (id: string) => {
         order.push(`create:${id}`);
         if (runtimes.size >= 1) throw new Error("max Pi processes reached");
@@ -211,13 +221,8 @@ test("POST /sessions reclaims a finalized runtime before enforcing the Pi limit"
       sessionNew: async () => {
         const id = `s${++nextId}`;
         order.push(`new:${id}`);
-        statuses.set(id, "open");
         return { id };
       },
-      sessionShow: async (id: string) => {
-        order.push(`show:${id}`);
-        return { status: statuses.get(id) };
-      },
       searchPack: async () => {},
       failSession: async () => {},
     } as any,
@@ -227,7 +232,6 @@ test("POST /sessions reclaims a finalized runtime before enforcing the Pi limit"
 
   expect((await app.inject({ method: "POST", url: "/sessions", payload: { question: "one" } })).statusCode)
     .toBe(200);
-  statuses.set("s1", "finalized");
   order.length = 0;
 
   const second = await app.inject({ method: "POST", url: "/sessions", payload: { question: "two" } });
@@ -235,7 +239,7 @@ test("POST /sessions reclaims a finalized runtime before enforcing the Pi limit"
   expect(second.statusCode).toBe(200);
   expect(second.json()).toEqual({ id: "s2" });
   expect(tornDown).toEqual(["s1"]);
-  expect(order).toEqual(["show:s1", "teardown:s1", "new:s2", "create:s2"]);
+  expect(order).toEqual(["teardown:s1", "new:s2", "create:s2"]);
   expect(runtimes.has("s2")).toBe(true);
 });
 
@@ -401,6 +405,52 @@ test("POST /sessions/:id/resume usa il thinking globale se manca nel manifest",
   expect(configured.thinking).toBe("low");
 });
 
+test("resuming a different session stops the user's previous Pi runtime", async () => {
+  const runtimes = new Map<string, any>();
+  const mgr = {
+    get: (id: string) => runtimes.get(id),
+    teardownForPrincipal: () => {
+      const stopped = [...runtimes.keys()];
+      runtimes.clear();
+      return stopped;
+    },
+    createFor: (id: string) => {
+      if (runtimes.size >= 1) throw new Error("max Pi processes reached");
+      const runtime = { bridge: { onClientEvent: () => {}, turnState: () => "running" } };
+      runtimes.set(id, runtime);
+      return runtime;
+    },
+    configure: async () => {},
+    start: () => {},
+    teardownIfCurrent: (id: string, expected: any) => {
+      if (runtimes.get(id) !== expected) return false;
+      runtimes.delete(id);
+      return true;
+    },
+  } as any;
+  const app = buildApp(loadConfig({ THT_HARNESS_DIR: "../harness" }), {
+    mgr,
+    thtRunner: {
+      sessionNew: async () => ({ id: "s1" }),
+      sessionShow: async (id: string) => ({ id, status: "open", archived: false }),
+      reopenSession: async () => {},
+      searchPack: async () => {},
+      failSession: async () => {},
+    } as any,
+    readiness: { ensure: async () => ({ ok: true }) } as any,
+    getSettings: () => ({ workspace: "local" }) as any,
+  });
+  expect((await app.inject({ method: "POST", url: "/sessions", payload: { question: "one" } })).statusCode)
+    .toBe(200);
+
+  const resumed = await app.inject({ method: "POST", url: "/sessions/s2/resume" });
+
+  expect(resumed.statusCode).toBe(200);
+  expect(resumed.json()).toEqual({ id: "s2", alreadyActive: false });
+  expect(runtimes.has("s1")).toBe(false);
+  expect(runtimes.has("s2")).toBe(true);
+});
+
 test.each(["running", "waiting"])(
   "POST resume preserves a %s runtime",
   async (state) => {