diff --git a/src/App.spec.ts b/src/App.spec.ts
index b604ed1..f804ca6 100644
--- a/src/App.spec.ts
+++ b/src/App.spec.ts
@@ -73,6 +73,36 @@ describe("App", () => {
     wrapper.unmount();
   });
 
+  it("cancels an in-flight turn without committing and explicitly retries it", async () => {
+    const wrapper = await mountLoadedApp();
+    const composer = wrapper.get<HTMLTextAreaElement>('textarea[aria-label="自由输入"]');
+    const startingNode = wrapper.get(".statusline span").text();
+
+    await composer.setValue("我先听听雨声。");
+    await wrapper.get("form.composer").trigger("submit");
+    expect(wrapper.get(".cancel-turn-button").text()).toBe("停止生成");
+    expect(wrapper.get(".turn-status").text()).toContain("只有完整回应通过校验后");
+
+    await wrapper.get(".cancel-turn-button").trigger("click");
+    expect(wrapper.get(".cancel-turn-button").text()).toBe("停止中…");
+
+    await vi.waitFor(() => {
+      expect(wrapper.get(".turn-status").text()).toContain("已停止生成");
+      expect(wrapper.get(".turn-status").text()).toContain("本轮没有写入故事");
+    });
+    expect(wrapper.get(".statusline span").text()).toBe(startingNode);
+    expect(wrapper.find(".beat--action").exists()).toBe(false);
+    expect(wrapper.get(".retry-turn-button").text()).toBe("重试本轮");
+
+    await wrapper.get(".retry-turn-button").trigger("click");
+    await vi.waitFor(() => {
+      expect(wrapper.get(".statusline span").text()).toBe("node_002");
+      expect(wrapper.text()).toContain("我先听听雨声。");
+    });
+    expect(wrapper.find(".retry-turn-button").exists()).toBe(false);
+    wrapper.unmount();
+  });
+
   it("finishes the playable before-dawn slice and exposes its settled records", async () => {
     const wrapper = await mountLoadedApp();
     const composer = wrapper.get<HTMLTextAreaElement>('textarea[aria-label="自由输入"]');
@@ -178,6 +208,22 @@ describe("App", () => {
     wrapper.unmount();
   });
 
+  it("offers a deterministic, credential-free LAPP connection check in preview", async () => {
+    const wrapper = await mountLoadedApp();
+    await wrapper.get('button[aria-label="模型设置"]').trigger("click");
+
+    const testButton = wrapper.get(".connection-test-button");
+    expect(testButton.attributes("disabled")).toBeUndefined();
+    await testButton.trigger("click");
+    await flushPromises();
+
+    const result = wrapper.get(".connection-result");
+    expect(result.attributes("data-tone")).toBe("preview");
+    expect(result.text()).toContain("真实 LAPP 连接需在桌面端测试");
+    expect(wrapper.get("#settings-panel").text()).not.toMatch(/api[_-]?key\s*[:=]/i);
+    wrapper.unmount();
+  });
+
   it("closes the active panel with Escape", async () => {
     const wrapper = await mountLoadedApp();
     await wrapper.findAll(".top-actions button")[0].trigger("click");
diff --git a/src/App.vue b/src/App.vue
index 92c9949..e342f67 100644
--- a/src/App.vue
+++ b/src/App.vue
@@ -9,17 +9,28 @@ const {
   appInfo,
   branchList,
   busy,
+  canRetryTurn,
+  cancellingTurn,
   error,
   lastSubmittedIntent,
   loading,
   lappSettings,
+  lappTestStatus,
   pack,
   playerView,
+  testingLappConnection,
+  turnFailure,
+  turnInFlight,
+  turnNotice,
+  cancelActiveTurn,
+  clearLappTestStatus,
   forkBranch,
   renameBranch,
+  retryTurn,
   selectLappModel,
   submitTurn,
   switchBranch,
+  testLappConnection,
   turnError
 } = useDemo();
 const draft = ref("");
@@ -139,6 +150,7 @@ function setLappSelection(event: Event) {
   const target = event.target;
   if (target instanceof HTMLSelectElement) {
     lappSelection.value = target.value;
+    clearLappTestStatus();
   }
 }
 
@@ -155,6 +167,15 @@ async function saveLappSelection() {
   await selectLappModel(providerId, modelId);
 }
 
+const canTestLappConnection = computed(() => {
+  const settings = lappSettings.value;
+  if (!settings) return false;
+  return (
+    settings.mode === "demo" ||
+    Boolean(settings.selectedProviderId && settings.selectedModelId)
+  );
+});
+
 function handleEscape(event: KeyboardEvent) {
   if (event.key === "Escape" && activePanel.value) {
     closePanel();
@@ -274,21 +295,60 @@ onBeforeUnmount(() => window.removeEventListener("keydown", handleEscape));
           :disabled="busy || !playerView.canContinue"
           @click="continueStory"
         >
-          {{ busy && lastSubmittedIntent === "continue" ? "继续中…" : "继续" }}
+          {{ turnInFlight && lastSubmittedIntent === "continue" ? "继续中…" : "继续" }}
         </button>
         <button
           class="send-button"
           type="submit"
           :disabled="busy || !playerView.canContinue || draft.trim().length === 0"
         >
-          {{ busy && lastSubmittedIntent === "speak_or_act" ? "发送中…" : "发送" }}
+          {{ turnInFlight && lastSubmittedIntent === "speak_or_act" ? "发送中…" : "发送" }}
         </button>
       </form>
 
-      <p class="turn-status" aria-live="polite">
-        <span v-if="busy">故事正在回应，请稍候。</span>
-        <span v-else-if="turnError">请求未完成：{{ turnError }}</span>
-      </p>
+      <section class="turn-status" aria-live="polite" aria-label="回合状态">
+        <div v-if="turnInFlight" class="turn-status-card turn-status-card--progress">
+          <span>
+            <strong>{{ cancellingTurn ? "正在停止本轮" : "故事正在回应" }}</strong>
+            <small>
+              {{
+                cancellingTurn
+                  ? "等待引擎确认；未完成的回合不会写入故事。"
+                  : turnNotice ?? "只有完整回应通过校验后，才会写入当前线路。"
+              }}
+            </small>
+          </span>
+          <button
+            class="cancel-turn-button"
+            type="button"
+            :disabled="cancellingTurn"
+            @click="cancelActiveTurn"
+          >
+            {{ cancellingTurn ? "停止中…" : "停止生成" }}
+          </button>
+        </div>
+        <div v-else-if="turnFailure" class="turn-status-card turn-status-card--failure">
+          <span>
+            <strong>{{ turnFailure.title }}</strong>
+            <small>{{ turnFailure.message }} {{ turnFailure.noCommitMessage }}</small>
+          </span>
+          <button
+            v-if="turnFailure.retryable"
+            class="retry-turn-button"
+            type="button"
+            :disabled="!canRetryTurn"
+            @click="retryTurn"
+          >
+            重试本轮
+          </button>
+        </div>
+        <div v-else-if="turnNotice" class="turn-status-card turn-status-card--notice">
+          <span>{{ turnNotice }}</span>
+        </div>
+        <div v-else-if="turnError" class="turn-status-card turn-status-card--failure">
+          <span>操作未完成：{{ turnError }}</span>
+        </div>
+      </section>
 
       <footer class="statusline">
         <span>{{ playerView.nodeId }}</span>
@@ -501,13 +561,34 @@ onBeforeUnmount(() => window.removeEventListener("keydown", handleEscape));
                   {{ model.providerName ?? model.providerId }} · {{ model.modelName ?? model.modelId }}
                 </option>
               </select>
-              <button
-                type="button"
-                :disabled="busy || !selectedLappValue || lappSettings.mode === 'demo'"
-                @click="saveLappSelection"
+              <div class="settings-actions">
+                <button
+                  type="button"
+                  :disabled="busy || !selectedLappValue || lappSettings.mode === 'demo'"
+                  @click="saveLappSelection"
+                >
+                  应用模型
+                </button>
+                <button
+                  class="connection-test-button"
+                  type="button"
+                  :disabled="busy || !canTestLappConnection"
+                  @click="testLappConnection"
+                >
+                  {{ testingLappConnection ? "测试中…" : "测试当前连接" }}
+                </button>
+              </div>
+              <small class="connection-privacy">
+                测试只确认当前模型能否完成最小请求，不读取、展示或保存 API Key。
+              </small>
+              <p
+                v-if="lappTestStatus"
+                class="connection-result"
+                :data-tone="lappTestStatus.tone"
+                role="status"
               >
-                {{ busy ? "正在应用…" : "应用模型" }}
-              </button>
+                {{ lappTestStatus.message }}
+              </p>
             </div>
           </div>
         </aside>
diff --git a/src/app/bridge.spec.ts b/src/app/bridge.spec.ts
index ae7edf8..bd9fe1e 100644
--- a/src/app/bridge.spec.ts
+++ b/src/app/bridge.spec.ts
@@ -21,11 +21,13 @@ vi.mock("@tauri-apps/api/core", () => ({
 }));
 
 import {
+  cancelTurn,
   forkBranch,
   getBranchList,
   getLappSettings,
   submitTurn,
   switchBranch,
+  testLappConnection,
   updateLappSettings
 } from "./bridge";
 
@@ -46,6 +48,7 @@ describe("Tauri bridge", () => {
 
   afterEach(() => {
     delete window.__TAURI_INTERNALS__;
+    vi.useRealTimers();
   });
 
   it("sends only TurnRequest to the submit_turn command", async () => {
@@ -62,6 +65,48 @@ describe("Tauri bridge", () => {
     expect(invokeMock).toHaveBeenCalledWith("submit_turn", { request });
   });
 
+  it("uses narrow commands for cancellation and a credential-free connection test", async () => {
+    const connectionRequest: UpdateLappSettingsRequest = {
+      providerId: "provider",
+      modelId: "model"
+    };
+    const connectionResult = {
+      ok: true,
+      providerId: connectionRequest.providerId,
+      modelId: connectionRequest.modelId,
+      message: "connected",
+      diagnosticCode: null
+    };
+    invokeMock.mockResolvedValueOnce(true).mockResolvedValueOnce(connectionResult);
+
+    await expect(cancelTurn(request.actionId)).resolves.toBe(true);
+    await expect(testLappConnection(connectionRequest)).resolves.toEqual(connectionResult);
+    expect(invokeMock.mock.calls).toEqual([
+      ["cancel_turn", { actionId: request.actionId }],
+      ["test_lapp_connection", { request: connectionRequest }]
+    ]);
+  });
+
+  it("deterministically discards a cancelled browser-preview result", async () => {
+    delete window.__TAURI_INTERNALS__;
+    vi.useFakeTimers();
+    const pending = submitTurn(request, initialView as PlayerView);
+    const rejection = expect(pending).rejects.toMatchObject({
+      code: "cancelled",
+      retryable: true
+    });
+
+    await expect(cancelTurn(request.actionId)).resolves.toBe(true);
+    await vi.runAllTimersAsync();
+    await rejection;
+    await expect(
+      testLappConnection({ providerId: "browser-preview", modelId: "deterministic-demo" })
+    ).resolves.toMatchObject({
+      ok: true,
+      diagnosticCode: "browser_preview"
+    });
+  });
+
   it("sends only the typed fork request to the fork_branch command", async () => {
     const forkRequest: ForkBranchRequest = {
       storyId: initialView.storyId,
diff --git a/src/app/bridge.ts b/src/app/bridge.ts
index 3788189..d986a4d 100644
--- a/src/app/bridge.ts
+++ b/src/app/bridge.ts
@@ -19,6 +19,17 @@ import type {
 
 import { forkDemoBranch, submitDemoTurn } from "./turnAdapter";
 
+interface LappConnectionTestResult {
+  ok: boolean;
+  providerId: string;
+  modelId: string;
+  message: string;
+  diagnosticCode: string | null;
+}
+
+const browserActiveTurns = new Set<string>();
+const browserCancelledTurns = new Set<string>();
+
 function isTauri(): boolean {
   return typeof window !== "undefined" && window.__TAURI_INTERNALS__ !== undefined;
 }
@@ -127,16 +138,69 @@ export async function updateLappSettings(
   return invoke<LappSettings>("update_lapp_settings", { request });
 }
 
+/**
+ * Tests only the currently applied LAPP model. The desktop command owns profile
+ * and credential access; no secret or provider response crosses this boundary.
+ */
+export async function testLappConnection(
+  request: UpdateLappSettingsRequest
+): Promise<LappConnectionTestResult> {
+  if (!isTauri()) {
+    await Promise.resolve();
+    return {
+      ok: true,
+      providerId: request.providerId,
+      modelId: request.modelId,
+      message: "browser preview is deterministic",
+      diagnosticCode: "browser_preview"
+    };
+  }
+
+  return invoke<LappConnectionTestResult>("test_lapp_connection", { request });
+}
+
 export async function submitTurn(
   request: TurnRequest,
   currentView: PlayerView
 ): Promise<TurnResult> {
   if (!isTauri()) {
-    return submitDemoTurn(request, currentView);
+    browserActiveTurns.add(request.actionId);
+    try {
+      const result = await submitDemoTurn(request, currentView);
+      if (browserCancelledTurns.has(request.actionId)) {
+        throw {
+          code: "cancelled",
+          message: "browser preview turn was cancelled",
+          retryable: true
+        };
+      }
+      return result;
+    } finally {
+      browserActiveTurns.delete(request.actionId);
+      browserCancelledTurns.delete(request.actionId);
+    }
   }
   return invoke<TurnResult>("submit_turn", { request });
 }
 
+/**
+ * Requests cancellation of an uncommitted turn. The original submit_turn
+ * promise remains authoritative: it must settle as either a complete commit or
+ * a structured `cancelled` failure.
+ */
+export async function cancelTurn(actionId: string): Promise<boolean> {
+  if (!isTauri()) {
+    if (browserActiveTurns.has(actionId)) {
+      browserCancelledTurns.add(actionId);
+      await Promise.resolve();
+      return true;
+    }
+    await Promise.resolve();
+    return false;
+  }
+  return invoke<boolean>("cancel_turn", { actionId });
+}
+
 export async function forkBranch(
   request: ForkBranchRequest,
   currentView: PlayerView
diff --git a/src/app/errors.spec.ts b/src/app/errors.spec.ts
new file mode 100644
index 0000000..372a45e
--- /dev/null
+++ b/src/app/errors.spec.ts
@@ -0,0 +1,56 @@
+import { describe, expect, it } from "vitest";
+
+import {
+  describeConnectionDiagnostic,
+  describeConnectionFailure,
+  describeOperationFailure,
+  describeTurnFailure
+} from "./errors";
+
+describe("player-safe failure copy", () => {
+  it("offers an immediate retry only for retryable turn failures", () => {
+    const retryable = describeTurnFailure({
+      code: "provider_unavailable",
+      message: "upstream secret diagnostic",
+      retryable: true
+    });
+    const invalid = describeTurnFailure({
+      code: "invalid_input",
+      message: "private validation detail",
+      retryable: false
+    });
+
+    expect(retryable.retryable).toBe(true);
+    expect(retryable.noCommitMessage).toContain("没有写入故事");
+    expect(invalid.retryable).toBe(false);
+  });
+
+  it("does not echo provider or hidden-check diagnostics", () => {
+    const privateDetail = "roll=97 target=42 api_key=do-not-show";
+    const turn = describeTurnFailure({
+      code: "invalid_model_output",
+      message: privateDetail,
+      retryable: true
+    });
+
+    expect(JSON.stringify(turn)).not.toContain(privateDetail);
+    expect(describeOperationFailure({ message: privateDetail })).not.toContain(privateDetail);
+    expect(describeConnectionFailure({ message: privateDetail })).not.toContain(privateDetail);
+    expect(describeConnectionDiagnostic("VAULT_CREDENTIAL_NOT_FOUND")).not.toContain(privateDetail);
+  });
+
+  it("does not suggest blindly retrying a stale branch", () => {
+    const failure = describeTurnFailure({
+      code: "stale_node",
+      retryable: true
+    });
+
+    expect(failure.retryable).toBe(false);
+    expect(failure.message).toContain("重新打开");
+  });
+
+  it("uses connection diagnostic codes without displaying provider text", () => {
+    expect(describeConnectionDiagnostic("WAIT_TIMEOUT")).toContain("超时");
+    expect(describeConnectionDiagnostic("VAULT_CREDENTIAL_NOT_FOUND")).toContain("LAPP Vault");
+  });
+});
diff --git a/src/app/errors.ts b/src/app/errors.ts
new file mode 100644
index 0000000..1f41b7d
--- /dev/null
+++ b/src/app/errors.ts
@@ -0,0 +1,166 @@
+export interface PlayerTurnFailure {
+  code: string;
+  title: string;
+  message: string;
+  retryable: boolean;
+  noCommitMessage: string;
+}
+
+interface CommandFailureShape {
+  code?: unknown;
+  retryable?: unknown;
+}
+
+interface FailureCopy {
+  title: string;
+  message: string;
+  retryableByDefault: boolean;
+  supportsImmediateRetry: boolean;
+}
+
+const NO_COMMIT_MESSAGE = "本轮没有写入故事，当前节点保持不变。";
+
+const TURN_FAILURE_COPY: Record<string, FailureCopy> = {
+  cancelled: {
+    title: "已停止生成",
+    message: "这次回应已被完整丢弃。",
+    retryableByDefault: true,
+    supportsImmediateRetry: true
+  },
+  timed_out: {
+    title: "等待模型超时",
+    message: "模型没有及时完成回应，可以重试本轮。",
+    retryableByDefault: true,
+    supportsImmediateRetry: true
+  },
+  provider_unavailable: {
+    title: "模型暂时不可用",
+    message: "请检查模型设置或网络连接，也可以稍后重试。",
+    retryableByDefault: true,
+    supportsImmediateRetry: true
+  },
+  invalid_model_output: {
+    title: "模型回应无法使用",
+    message: "回应未通过完整性校验，可以重新生成本轮。",
+    retryableByDefault: true,
+    supportsImmediateRetry: true
+  },
+  storage_unavailable: {
+    title: "存档暂时不可用",
+    message: "故事未能安全保存，请稍后重试。",
+    retryableByDefault: true,
+    supportsImmediateRetry: true
+  },
+  internal: {
+    title: "本轮未能完成",
+    message: "应用遇到临时问题，可以重试本轮。",
+    retryableByDefault: true,
+    supportsImmediateRetry: true
+  },
+  turn_in_progress: {
+    title: "已有一轮正在生成",
+    message: "请等待正在进行的回合结束，再重试本轮。",
+    retryableByDefault: true,
+    supportsImmediateRetry: true
+  },
+  stale_node: {
+    title: "故事线路已经变化",
+    message: "当前画面不是最新节点，请重新打开对应线路后再行动。",
+    retryableByDefault: false,
+    supportsImmediateRetry: false
+  },
+  invalid_input: {
+    title: "这次行动无法提交",
+    message: "请调整输入后再试。",
+    retryableByDefault: false,
+    supportsImmediateRetry: false
+  }
+};
+
+function commandFailure(reason: unknown): CommandFailureShape | null {
+  if (typeof reason !== "object" || reason === null) return null;
+  return reason as CommandFailureShape;
+}
+
+function normalizedCode(reason: unknown): string {
+  const code = commandFailure(reason)?.code;
+  return typeof code === "string" && code.trim() ? code.trim().toLowerCase() : "unknown";
+}
+
+/**
+ * Converts a backend failure into player-safe copy.
+ *
+ * The backend message is intentionally not echoed: provider diagnostics may
+ * contain implementation details that do not belong in PlayerView-facing UI.
+ */
+export function describeTurnFailure(reason: unknown): PlayerTurnFailure {
+  const failure = commandFailure(reason);
+  const code = normalizedCode(reason);
+  const copy = TURN_FAILURE_COPY[code] ?? {
+    title: "请求没有完成",
+    message: "本轮没有产生可用的回应。",
+    retryableByDefault: false,
+    supportsImmediateRetry: true
+  };
+  const retryable =
+    copy.supportsImmediateRetry &&
+    (typeof failure?.retryable === "boolean" ? failure.retryable : copy.retryableByDefault);
+
+  return {
+    code,
+    title: copy.title,
+    message: copy.message,
+    retryable,
+    noCommitMessage: NO_COMMIT_MESSAGE
+  };
+}
+
+export function describeOperationFailure(reason: unknown): string {
+  switch (normalizedCode(reason)) {
+    case "timed_out":
+      return "操作等待超时，请稍后重试。";
+    case "provider_unavailable":
+      return "当前模型不可用，请检查模型设置。";
+    case "storage_unavailable":
+      return "故事存档暂时不可用，请稍后重试。";
+    case "stale_node":
+      return "故事线路已经变化，请重新打开对应线路。";
+    case "invalid_input":
+      return "提交的内容无法使用，请检查后重试。";
+    default:
+      return "操作没有完成，请稍后重试。";
+  }
+}
+
+export function describeConnectionFailure(reason: unknown): string {
+  switch (normalizedCode(reason)) {
+    case "timed_out":
+      return "连接测试超时，请检查网络后重试。";
+    case "provider_unavailable":
+      return "当前模型无法连接，请检查 LAPP profile 与网络。";
+    case "invalid_input":
+      return "当前模型配置不完整，请先应用可用模型。";
+    default:
+      return "连接测试没有完成；没有读取或显示任何凭据。";
+  }
+}
+
+export function describeConnectionDiagnostic(code: string | null): string {
+  switch (code?.toUpperCase()) {
+    case "ENV_SECRET_MISSING":
+    case "VAULT_BACKEND_UNAVAILABLE":
+    case "VAULT_CREDENTIAL_NOT_FOUND":
+    case "VAULT_BINDING_MISMATCH":
+    case "VAULT_ACCESS_DENIED":
+      return "LAPP profile 引用的凭据当前不可用，请在 LAPP Vault 中检查配置。";
+    case "WAIT_TIMEOUT":
+      return "最小请求等待超时，请检查网络后重试。";
+    case "HTTP_REQUEST_FAILED":
+    case "HTTP_STATUS":
+      return "供应商连接失败，请检查网络与模型服务状态。";
+    case "INVALID_RESPONSE":
+      return "模型返回了无法识别的响应，请确认所选协议与模型兼容。";
+    default:
+      return "当前模型没有完成最小请求，请检查 LAPP profile 与网络。";
+  }
+}
diff --git a/src/app/useDemo.ts b/src/app/useDemo.ts
index 915dc26..3f00f73 100644
--- a/src/app/useDemo.ts
+++ b/src/app/useDemo.ts
@@ -1,4 +1,4 @@
-import { onMounted, ref } from "vue";
+import { computed, onMounted, ref } from "vue";
 
 import type {
   AppInfo,
@@ -11,6 +11,7 @@ import type {
 } from "@contracts";
 
 import {
+  cancelTurn as cancelRuntimeTurn,
   forkBranch as forkRuntimeBranch,
   getAppInfo,
   getBranchList,
@@ -18,22 +19,30 @@ import {
   getDemoPlayerView,
   getLappSettings,
   renameBranch as renameRuntimeBranch,
+  submitTurn as submitRuntimeTurn,
   switchBranch as switchRuntimeBranch,
-  updateLappSettings,
-  submitTurn as submitRuntimeTurn
+  testLappConnection as testRuntimeLappConnection,
+  updateLappSettings
 } from "./bridge";
+import {
+  describeConnectionDiagnostic,
+  describeConnectionFailure,
+  describeOperationFailure,
+  describeTurnFailure,
+  type PlayerTurnFailure
+} from "./errors";
 
-function errorMessage(reason: unknown): string {
-  if (reason instanceof Error) return reason.message;
-  if (
-    typeof reason === "object" &&
-    reason !== null &&
-    "message" in reason &&
-    typeof reason.message === "string"
-  ) {
-    return reason.message;
-  }
-  return String(reason);
+type TurnPhase = "idle" | "submitting" | "cancelling";
+
+interface TurnAttempt {
+  request: TurnRequest;
+  sourceView: PlayerView;
+  intent: TurnIntent;
+}
+
+export interface LappTestStatus {
+  tone: "success" | "error" | "preview";
+  message: string;
 }
 
 export function useDemo() {
@@ -46,22 +55,35 @@ export function useDemo() {
   const error = ref<string | null>(null);
   const busy = ref(false);
   const turnError = ref<string | null>(null);
+  const turnFailure = ref<PlayerTurnFailure | null>(null);
+  const turnNotice = ref<string | null>(null);
+  const turnPhase = ref<TurnPhase>("idle");
   const lastSubmittedIntent = ref<TurnIntent | null>(null);
+  const testingLappConnection = ref(false);
+  const lappTestStatus = ref<LappTestStatus | null>(null);
   const branchViews = new Map<string, PlayerView>();
+  let activeTurn: TurnAttempt | null = null;
+  let retryableTurn: TurnAttempt | null = null;
+
+  const turnInFlight = computed(() => turnPhase.value !== "idle");
+  const cancellingTurn = computed(() => turnPhase.value === "cancelling");
+  const canRetryTurn = computed(
+    () => !busy.value && Boolean(retryableTurn && turnFailure.value?.retryable)
+  );
 
   onMounted(async () => {
     try {
       [appInfo.value, pack.value, playerView.value, branchList.value, lappSettings.value] =
         await Promise.all([
-        getAppInfo(),
-        getDemoPackSummary(),
-        getDemoPlayerView(),
-        getBranchList(),
-        getLappSettings()
-      ]);
+          getAppInfo(),
+          getDemoPackSummary(),
+          getDemoPlayerView(),
+          getBranchList(),
+          getLappSettings()
+        ]);
       if (playerView.value) branchViews.set(playerView.value.branchId, playerView.value);
     } catch (reason) {
-      error.value = errorMessage(reason);
+      error.value = describeOperationFailure(reason);
     } finally {
       loading.value = false;
     }
@@ -84,28 +106,89 @@ export function useDemo() {
       input: intent === "continue" ? "" : normalizedInput
     };
 
+    await runTurn({ request, sourceView: currentView, intent });
+  }
+
+  async function runTurn(attempt: TurnAttempt): Promise<void> {
+    if (busy.value) return;
+
     busy.value = true;
     turnError.value = null;
-    lastSubmittedIntent.value = intent;
+    turnFailure.value = null;
+    turnNotice.value = null;
+    retryableTurn = null;
+    turnPhase.value = "submitting";
+    lastSubmittedIntent.value = attempt.intent;
+    activeTurn = attempt;
 
     try {
-      const result = await submitRuntimeTurn(request, currentView);
+      const result = await submitRuntimeTurn(attempt.request, attempt.sourceView);
+      const cancellationWasRequested = cancellingTurn.value;
       playerView.value = result.playerView;
       branchViews.set(result.playerView.branchId, result.playerView);
       updateBranchHead(result.playerView);
+      turnNotice.value = cancellationWasRequested
+        ? "本轮在停止请求生效前已经完整完成，并已安全写入故事。"
+        : null;
     } catch (reason) {
-      turnError.value = errorMessage(reason);
+      const failure = describeTurnFailure(reason);
+      turnFailure.value = failure;
+      retryableTurn = failure.retryable ? attempt : null;
     } finally {
+      if (activeTurn === attempt) activeTurn = null;
+      turnPhase.value = "idle";
       busy.value = false;
     }
   }
 
+  async function cancelActiveTurn(): Promise<void> {
+    const attempt = activeTurn;
+    if (!attempt || turnPhase.value !== "submitting") return;
+
+    turnPhase.value = "cancelling";
+    turnNotice.value = null;
+    try {
+      const accepted = await cancelRuntimeTurn(attempt.request.actionId);
+      if (!accepted && activeTurn === attempt) {
+        turnPhase.value = "submitting";
+        turnNotice.value = "停止请求没有抢在提交前生效；正在等待本轮的最终结果。";
+      }
+    } catch (reason) {
+      if (activeTurn === attempt) {
+        turnPhase.value = "submitting";
+        turnNotice.value = `${describeOperationFailure(reason)} 当前回合仍在等待完成。`;
+      }
+    }
+  }
+
+  async function retryTurn(): Promise<void> {
+    const attempt = retryableTurn;
+    const currentView = playerView.value;
+    if (!attempt || !currentView || busy.value) return;
+
+    if (
+      currentView.storyId !== attempt.request.storyId ||
+      currentView.branchId !== attempt.request.branchId ||
+      currentView.nodeId !== attempt.request.expectedNodeId
+    ) {
+      retryableTurn = null;
+      turnFailure.value = describeTurnFailure({
+        code: "stale_node",
+        retryable: false
+      });
+      return;
+    }
+
+    // Keep the original action id: desktop retries can therefore be idempotent.
+    await runTurn(attempt);
+  }
+
   async function forkBranch(sourceNodeId: string): Promise<void> {
     const currentView = playerView.value;
     if (!currentView || busy.value || sourceNodeId === currentView.nodeId) return;
 
     busy.value = true;
-    turnError.value = null;
+    clearTurnFeedback();
     lastSubmittedIntent.value = null;
 
     try {
@@ -142,7 +225,7 @@ export function useDemo() {
         };
       }
     } catch (reason) {
-      turnError.value = errorMessage(reason);
+      turnError.value = describeOperationFailure(reason);
     } finally {
       busy.value = false;
     }
@@ -154,7 +237,7 @@ export function useDemo() {
     if (!currentView || !branches || busy.value || branchId === currentView.branchId) return;
 
     busy.value = true;
-    turnError.value = null;
+    clearTurnFeedback();
     lastSubmittedIntent.value = null;
     branchViews.set(currentView.branchId, currentView);
 
@@ -178,7 +261,7 @@ export function useDemo() {
         }))
       };
     } catch (reason) {
-      turnError.value = errorMessage(reason);
+      turnError.value = describeOperationFailure(reason);
     } finally {
       busy.value = false;
     }
@@ -190,14 +273,14 @@ export function useDemo() {
     if (!branches || busy.value || !normalized) return;
 
     busy.value = true;
-    turnError.value = null;
+    clearTurnFeedback();
     try {
       branchList.value = await renameRuntimeBranch(
         { storyId: branches.storyId, branchId, name: normalized },
         branches
       );
     } catch (reason) {
-      turnError.value = errorMessage(reason);
+      turnError.value = describeOperationFailure(reason);
     } finally {
       busy.value = false;
     }
@@ -206,16 +289,83 @@ export function useDemo() {
   async function selectLappModel(providerId: string, modelId: string): Promise<void> {
     if (busy.value) return;
     busy.value = true;
-    turnError.value = null;
+    lappTestStatus.value = null;
     try {
       lappSettings.value = await updateLappSettings({ providerId, modelId });
     } catch (reason) {
-      turnError.value = errorMessage(reason);
+      lappTestStatus.value = {
+        tone: "error",
+        message: describeOperationFailure(reason)
+      };
     } finally {
       busy.value = false;
     }
   }
 
+  async function testLappConnection(): Promise<void> {
+    const settings = lappSettings.value;
+    if (!settings || busy.value) return;
+    if (
+      settings.mode !== "demo" &&
+      (!settings.selectedProviderId || !settings.selectedModelId)
+    ) {
+      lappTestStatus.value = {
+        tone: "error",
+        message: "请先应用一个支持聊天与工具调用的模型。"
+      };
+      return;
+    }
+
+    busy.value = true;
+    testingLappConnection.value = true;
+    lappTestStatus.value = null;
+    try {
+      const request =
+        settings.mode === "demo"
+          ? { providerId: "browser-preview", modelId: "deterministic-demo" }
+          : {
+              providerId: settings.selectedProviderId!,
+              modelId: settings.selectedModelId!
+            };
+      const result = await testRuntimeLappConnection(request);
+      if (result.diagnosticCode === "browser_preview") {
+        lappTestStatus.value = {
+          tone: "preview",
+          message: "浏览器演示路径正常；真实 LAPP 连接需在桌面端测试。"
+        };
+      } else if (result.ok) {
+        lappTestStatus.value = {
+          tone: "success",
+          message: "连接测试通过，当前模型可用于新的故事回合。"
+        };
+      } else {
+        lappTestStatus.value = {
+          tone: "error",
+          message: describeConnectionDiagnostic(result.diagnosticCode)
+        };
+      }
+    } catch (reason) {
+      lappTestStatus.value = {
+        tone: "error",
+        message: describeConnectionFailure(reason)
+      };
+    } finally {
+      testingLappConnection.value = false;
+      busy.value = false;
+    }
+  }
+
+  function clearLappTestStatus(): void {
+    lappTestStatus.value = null;
+  }
+
+  function clearTurnFeedback(): void {
+    turnError.value = null;
+    turnFailure.value = null;
+    turnNotice.value = null;
+    retryableTurn = null;
+  }
+
   function currentHistoryLabel(view: PlayerView): string {
     return view.history.find((node) => node.isCurrent)?.label ?? view.sceneTitle;
   }
@@ -243,17 +393,28 @@ export function useDemo() {
     appInfo,
     branchList,
     busy,
+    canRetryTurn,
+    cancellingTurn,
     error,
     lastSubmittedIntent,
-    loading,
     lappSettings,
+    lappTestStatus,
+    loading,
     pack,
     playerView,
+    testingLappConnection,
+    turnError,
+    turnFailure,
+    turnInFlight,
+    turnNotice,
+    cancelActiveTurn,
+    clearLappTestStatus,
     forkBranch,
     renameBranch,
+    retryTurn,
     selectLappModel,
     submitTurn,
     switchBranch,
-    turnError
+    testLappConnection
   };
 }
diff --git a/src/styles/main.css b/src/styles/main.css
index 26551ad..0390703 100644
--- a/src/styles/main.css
+++ b/src/styles/main.css
@@ -431,15 +431,86 @@ textarea:focus-visible {
 
 .turn-status {
   position: absolute;
-  right: 18%;
-  bottom: 18px;
-  z-index: 14;
+  right: 7%;
+  bottom: 108px;
+  z-index: 16;
+  width: min(620px, 72%);
   margin: 0;
-  color: rgb(241 196 178 / 72%);
-  font-size: 11px;
   pointer-events: none;
 }
 
+.turn-status-card {
+  display: flex;
+  min-height: 54px;
+  align-items: center;
+  justify-content: space-between;
+  gap: 18px;
+  padding: 10px 12px 10px 16px;
+  color: rgb(245 241 234 / 78%);
+  font-size: 12px;
+  background: rgb(11 14 23 / 94%);
+  border: 1px solid rgb(255 255 255 / 12%);
+  border-radius: 11px;
+  box-shadow: 0 12px 34px rgb(0 0 0 / 32%);
+  backdrop-filter: blur(16px);
+  pointer-events: auto;
+}
+
+.turn-status-card > span {
+  display: grid;
+  gap: 3px;
+  line-height: 1.45;
+}
+
+.turn-status-card strong {
+  color: rgb(247 243 237 / 88%);
+  font-weight: 600;
+}
+
+.turn-status-card small {
+  color: rgb(245 241 234 / 48%);
+  font-size: 11px;
+}
+
+.turn-status-card--progress {
+  border-color: rgb(184 205 222 / 24%);
+}
+
+.turn-status-card--failure {
+  border-color: rgb(231 167 167 / 32%);
+}
+
+.turn-status-card--notice {
+  min-height: 40px;
+  color: rgb(211 224 231 / 72%);
+}
+
+.turn-status-card button {
+  flex: 0 0 auto;
+  padding: 8px 12px;
+  cursor: pointer;
+  color: rgb(245 241 234 / 78%);
+  background: rgb(255 255 255 / 5%);
+  border: 1px solid rgb(255 255 255 / 14%);
+  border-radius: 8px;
+}
+
+.turn-status-card button:hover:not(:disabled) {
+  color: #f4c8b5;
+  border-color: rgb(231 184 164 / 38%);
+}
+
+.turn-status-card button:disabled {
+  cursor: default;
+  opacity: 0.46;
+}
+
+.turn-status-card .retry-turn-button {
+  color: #241b1a;
+  background: #e7b8a4;
+  border-color: transparent;
+}
+
 .statusline {
   position: absolute;
   right: 8%;
@@ -687,7 +758,8 @@ textarea:focus-visible {
 
 .branch-heading,
 .branch-actions,
-.settings-status {
+.settings-status,
+.settings-actions {
   display: flex;
   align-items: center;
   justify-content: space-between;
@@ -733,7 +805,7 @@ textarea:focus-visible {
 }
 
 .branch-actions button,
-.settings-card button {
+.settings-actions button {
   padding: 8px 10px;
   cursor: pointer;
   color: rgb(245 241 234 / 72%);
@@ -743,7 +815,7 @@ textarea:focus-visible {
 }
 
 .branch-actions button:disabled,
-.settings-card button:disabled {
+.settings-actions button:disabled {
   cursor: default;
   opacity: 0.42;
 }
@@ -778,6 +850,46 @@ textarea:focus-visible {
   background: #f3f0eb;
 }
 
+.settings-actions {
+  align-items: stretch;
+}
+
+.settings-actions button {
+  flex: 1;
+}
+
+.settings-actions .connection-test-button {
+  color: #eac0ae;
+  border-color: rgb(231 184 164 / 24%);
+}
+
+.settings-card .connection-privacy {
+  color: rgb(245 241 234 / 34%);
+  font-size: 10px;
+  line-height: 1.6;
+}
+
+.settings-card .connection-result {
+  padding: 10px 12px;
+  color: rgb(211 224 231 / 72%);
+  font-size: 12px;
+  background: rgb(123 164 190 / 8%);
+  border: 1px solid rgb(123 164 190 / 18%);
+  border-radius: 8px;
+}
+
+.settings-card .connection-result[data-tone="success"] {
+  color: #b9dac6;
+  background: rgb(118 184 143 / 8%);
+  border-color: rgb(118 184 143 / 20%);
+}
+
+.settings-card .connection-result[data-tone="error"] {
+  color: #e7b0aa;
+  background: rgb(205 113 113 / 8%);
+  border-color: rgb(205 113 113 / 20%);
+}
+
 .settings-status span[data-mode="unavailable"] {
   color: #e7a7a7;
   border-color: rgb(231 167 167 / 28%);