fix(security): sanitize session bootstrap failures

backend/test/routes-sessions.test.ts

@@ -471,3 +471,51 @@ test("POST /sessions returns after bridge attachment but starts only after retri
   await new Promise((resolve) => setImmediate(resolve));
   expect(started).toBe(true);
 });
+
+test("POST /sessions bootstrap failure emits only a fixed recovery message", async () => {
+  const published: Array<{ event: string; data: any }> = [];
+  let listener: ((event: any) => void) | undefined;
+  const bridge = {
+    onClientEvent: (callback: (event: any) => void) => { listener = callback; },
+    emitClientEvent: (event: any) => listener?.(event),
+  };
+  const runtime = { bridge } as any;
+  const rawFailure =
+    "connect https://secret.invalid/bootstrap?token=DO_NOT_LEAK using /srv/private/model-key";
+  const app = buildApp(loadConfig({ THT_HARNESS_DIR: "../harness" }), {
+    mgr: {
+      createFor: () => runtime,
+      configure: async () => { throw new Error(rawFailure); },
+      start: () => {},
+      teardown: () => {},
+    } as any,
+    hub: {
+      publish: (_id: string, event: string, data: any) => published.push({ event, data }),
+    } as any,
+    thtRunner: {
+      ollamaEnsure: async () => ({ ok: true }),
+      sessionNew: async () => ({ id: "s-bootstrap" }),
+      searchPack: async () => {},
+      failSession: async () => {},
+    } as any,
+    getSettings: () => ({ workspace: "psd" }) as any,
+  });
+
+  const response = await app.inject({
+    method: "POST",
+    url: "/sessions",
+    payload: { question: "q" },
+  });
+  await new Promise((resolve) => setImmediate(resolve));
+
+  expect(response.json()).toEqual({ id: "s-bootstrap" });
+  expect(published.map(({ data }) => data)).toContainEqual({
+    type: "info",
+    level: "error",
+    text: "Session startup failed. Check configuration and connectivity, then Resume the session.",
+  });
+  const clientOutput = JSON.stringify(published);
+  expect(clientOutput).not.toContain("secret.invalid");
+  expect(clientOutput).not.toContain("DO_NOT_LEAK");
+  expect(clientOutput).not.toContain("/srv/private/model-key");
+});