diff --git a/src/api/aiGenerationClient.ts b/src/api/aiGenerationClient.ts
index db00e1f..bfdc128 100644
--- a/src/api/aiGenerationClient.ts
+++ b/src/api/aiGenerationClient.ts
@@ -1,12 +1,18 @@
 import {
   buildApiUrl,
   buildAuthHeaders,
-  isRecord,
   readJsonResponse,
   serverRequest,
   throwResponseError,
 } from "./serverConnection";
 import { isOptionalApiRouteMissing } from "./apiErrorUtils";
+import {
+  parseAiTaskStatus,
+  parseAiTaskStatusList,
+  parseImageTaskCreateResponse,
+  parseSseTaskFrame,
+  parseTaskCreateResponse,
+} from "./dtoParsers";
 import type { WebGenerationPreviewTask } from "../types";
 
 export interface ImageGenInput {
@@ -190,13 +196,6 @@ function parseContentDispositionFilename(value: string | null): string | undefin
   return plainMatch?.[1]?.trim() || undefined;
 }
 
-function extractTaskList(payload: unknown): AiTaskStatus[] {
-  if (Array.isArray(payload)) return payload as AiTaskStatus[];
-  if (!isRecord(payload)) return [];
-  const rows = payload.tasks ?? payload.items;
-  return Array.isArray(rows) ? (rows as AiTaskStatus[]) : [];
-}
-
 function getStoredSessionRole(): string {
   try {
     if (typeof window === "undefined") return "";
@@ -251,67 +250,73 @@ export const aiGenerationClient = {
       projectId: input.projectId,
       conversationId: input.conversationId,
     });
-    const payload = await serverRequest<ImageTaskCreateResponse>("ai/image", {
+    const payload = await serverRequest<unknown>("ai/image", {
       method: "POST",
       body: input,
       timeoutMs: TASK_SUBMIT_TIMEOUT_MS,
       maxRetries: NON_RETRYING_REQUEST.maxRetries,
       fallbackMessage: "Image generation request failed",
     });
-    if (payload.providerDebug) {
-      emitImageRouteDebug("[ai/image-provider-debug]", payload.providerDebug as Record<string, unknown>);
+    const parsed = parseImageTaskCreateResponse(payload);
+    if (parsed.providerDebug) {
+      emitImageRouteDebug("[ai/image-provider-debug]", parsed.providerDebug as Record<string, unknown>);
     }
-    return payload;
+    return parsed;
   },
 
   async createVideoTask(input: VideoGenInput): Promise<{ taskId: string }> {
-    return serverRequest<{ taskId: string }>("ai/video", {
+    const payload = await serverRequest<unknown>("ai/video", {
       method: "POST",
       body: input,
       timeoutMs: TASK_SUBMIT_TIMEOUT_MS,
       maxRetries: NON_RETRYING_REQUEST.maxRetries,
       fallbackMessage: "Video generation request failed",
     });
+    return parseTaskCreateResponse(payload);
   },
 
   async createVideoSuperResolveTask(input: VideoSuperResolveInput): Promise<{ taskId: string }> {
-    return serverRequest<{ taskId: string }>("ai/video/super-resolve", {
+    const payload = await serverRequest<unknown>("ai/video/super-resolve", {
       method: "POST",
       body: input,
       timeoutMs: TASK_SUBMIT_TIMEOUT_MS,
       maxRetries: NON_RETRYING_REQUEST.maxRetries,
       fallbackMessage: "Video super-resolution request failed",
     });
+    return parseTaskCreateResponse(payload);
   },
 
   async createEraseSubtitlesTask(input: EraseSubtitlesInput): Promise<{ taskId: string }> {
-    return serverRequest<{ taskId: string }>("ai/video/erase-subtitles", {
+    const payload = await serverRequest<unknown>("ai/video/erase-subtitles", {
       method: "POST",
       body: input,
       timeoutMs: TASK_SUBMIT_TIMEOUT_MS,
       maxRetries: NON_RETRYING_REQUEST.maxRetries,
       fallbackMessage: "Subtitle removal request failed",
     });
+    return parseTaskCreateResponse(payload);
   },
 
   async createImageSuperResolveTask(input: ImageSuperResolveInput): Promise<{ taskId: string }> {
-    return serverRequest<{ taskId: string }>("ai/image/super-resolve", {
+    const payload = await serverRequest<unknown>("ai/image/super-resolve", {
       method: "POST",
       body: input,
       timeoutMs: TASK_SUBMIT_TIMEOUT_MS,
       maxRetries: NON_RETRYING_REQUEST.maxRetries,
       fallbackMessage: "Image super-resolution request failed",
     });
+    return parseTaskCreateResponse(payload);
   },
 
   async createImageEditTask(input: ImageEditInput): Promise<{ taskId: string }> {
-    return serverRequest<{ taskId: string }>("ai/image/edit", {
+    const payload = await serverRequest<unknown>("ai/image/edit", {
       method: "POST",
       body: input,
       timeoutMs: TASK_SUBMIT_TIMEOUT_MS,
       maxRetries: NON_RETRYING_REQUEST.maxRetries,
       fallbackMessage: "Image edit request failed",
     });
+    return parseTaskCreateResponse(payload);
   },
 
   async cancelTask(taskId: string): Promise<void> {
@@ -328,10 +333,11 @@ export const aiGenerationClient = {
   },
 
   async getTaskStatus(taskId: string): Promise<AiTaskStatus> {
-    return serverRequest<AiTaskStatus>(`ai/tasks/${taskId}`, {
+    const payload = await serverRequest<unknown>(`ai/tasks/${taskId}`, {
       timeoutMs: TASK_STATUS_TIMEOUT_MS,
       fallbackMessage: "Task status request failed",
     });
+    return parseAiTaskStatus(payload);
   },
 
   async downloadTaskResult(taskId: string): Promise<{ blob: Blob; filename?: string; contentType?: string }> {
@@ -361,7 +367,7 @@ export const aiGenerationClient = {
       const payload = await serverRequest<unknown>(`ai/tasks${search.toString() ? `?${search}` : ""}`, {
         fallbackMessage: "Task history request failed",
       });
-      return extractTaskList(payload).map(toPreviewTask);
+      return parseAiTaskStatusList(payload).map(toPreviewTask);
     } catch (error) {
       if (isOptionalApiRouteMissing(error)) {
         taskHistoryRouteMissing = true;
@@ -451,7 +457,7 @@ export const aiGenerationClient = {
             if (!line.startsWith("data: ")) continue;
             try {
               const data = JSON.parse(line.slice(6));
-              onUpdate(data);
+              onUpdate(parseSseTaskFrame(data));
             } catch { /* ignore */ }
           }
         }
diff --git a/src/api/dtoParsers.test.ts b/src/api/dtoParsers.test.ts
new file mode 100644
index 0000000..6d406eb
--- /dev/null
+++ b/src/api/dtoParsers.test.ts
@@ -0,0 +1,184 @@
+import { describe, it, expect } from "vitest";
+import {
+  parseAiTaskStatus,
+  parseTaskCreateResponse,
+  parseImageTaskCreateResponse,
+  parseAiTaskStatusList,
+  parseSseTaskFrame,
+} from "./dtoParsers";
+
+describe("parseAiTaskStatus", () => {
+  it("parses a well-formed camelCase DTO", () => {
+    const result = parseAiTaskStatus({
+      taskId: "task-1",
+      type: "video",
+      status: "running",
+      progress: 42,
+      resultUrl: "https://example.com/r.mp4",
+      error: null,
+      createdAt: "2026-01-01T00:00:00Z",
+      updatedAt: "2026-01-01T00:01:00Z",
+    });
+    expect(result.taskId).toBe("task-1");
+    expect(result.type).toBe("video");
+    expect(result.status).toBe("running");
+    expect(result.progress).toBe(42);
+    expect(result.resultUrl).toBe("https://example.com/r.mp4");
+  });
+
+  it("tolerates snake_case field names", () => {
+    const result = parseAiTaskStatus({
+      task_id: "task-2",
+      result_url: "https://example.com/x.png",
+      created_at: "2026-01-01T00:00:00Z",
+      updated_at: "2026-01-01T00:00:00Z",
+    });
+    expect(result.taskId).toBe("task-2");
+    expect(result.resultUrl).toBe("https://example.com/x.png");
+  });
+
+  it("falls back to safe defaults for missing fields", () => {
+    const result = parseAiTaskStatus({});
+    expect(result.taskId).toBe("");
+    expect(result.type).toBe("image");
+    expect(result.status).toBe("failed");
+    expect(result.progress).toBe(0);
+    expect(result.resultUrl).toBeNull();
+    expect(result.error).toBeNull();
+  });
+
+  it("rejects unknown status/type values", () => {
+    const result = parseAiTaskStatus({ status: "weird", type: "audio" });
+    expect(result.status).toBe("failed");
+    expect(result.type).toBe("image");
+  });
+
+  it("clamps progress to [0, 100]", () => {
+    expect(parseAiTaskStatus({ progress: 150 }).progress).toBe(100);
+    expect(parseAiTaskStatus({ progress: -10 }).progress).toBe(0);
+    expect(parseAiTaskStatus({ progress: "not-a-number" }).progress).toBe(0);
+  });
+
+  it("preserves numeric conversationId and nulls others", () => {
+    expect(parseAiTaskStatus({ conversationId: 7 }).conversationId).toBe(7);
+    expect(parseAiTaskStatus({ conversation_id: 9 }).conversationId).toBe(9);
+    expect(parseAiTaskStatus({ conversationId: "nope" }).conversationId).toBeNull();
+    expect(parseAiTaskStatus({}).conversationId).toBeNull();
+  });
+
+  it("returns empty string for a non-record payload", () => {
+    const result = parseAiTaskStatus("garbage");
+    expect(result.taskId).toBe("");
+    expect(result.status).toBe("failed");
+  });
+});
+
+describe("parseTaskCreateResponse", () => {
+  it("extracts taskId from a create response", () => {
+    expect(parseTaskCreateResponse({ taskId: "abc" }).taskId).toBe("abc");
+    expect(parseTaskCreateResponse({ task_id: "def" }).taskId).toBe("def");
+    expect(parseTaskCreateResponse({ id: "ghi" }).taskId).toBe("ghi");
+  });
+
+  it("throws when taskId is missing", () => {
+    expect(() => parseTaskCreateResponse({})).toThrow();
+    expect(() => parseTaskCreateResponse({ taskId: "" })).toThrow();
+    expect(() => parseTaskCreateResponse({ taskId: "  " })).toThrow();
+  });
+});
+
+describe("parseImageTaskCreateResponse", () => {
+  it("includes providerDebug when present", () => {
+    const result = parseImageTaskCreateResponse({
+      taskId: "img-1",
+      providerDebug: {
+        requestedModel: "gpt-image",
+        effectiveModel: "dall-e-3",
+        route: ["primary", "fallback"],
+        candidates: [{ provider: "openai", model: "dall-e-3" }],
+      },
+    });
+    expect(result.taskId).toBe("img-1");
+    expect(result.providerDebug?.effectiveModel).toBe("dall-e-3");
+    expect(result.providerDebug?.route).toEqual(["primary", "fallback"]);
+    expect(result.providerDebug?.candidates?.[0]?.model).toBe("dall-e-3");
+  });
+
+  it("omits providerDebug when absent", () => {
+    const result = parseImageTaskCreateResponse({ taskId: "img-2" });
+    expect(result.taskId).toBe("img-2");
+    expect(result.providerDebug).toBeUndefined();
+  });
+
+  it("tolerates snake_case providerDebug fields", () => {
+    const result = parseImageTaskCreateResponse({
+      taskId: "img-3",
+      provider_debug: { requested_model: "x", primary_provider: "openai" },
+    });
+    expect(result.providerDebug?.requestedModel).toBe("x");
+    expect(result.providerDebug?.primaryProvider).toBe("openai");
+  });
+
+  it("throws when taskId missing even if providerDebug present", () => {
+    expect(() => parseImageTaskCreateResponse({ providerDebug: {} })).toThrow();
+  });
+});
+
+describe("parseAiTaskStatusList", () => {
+  it("parses a bare array", () => {
+    const result = parseAiTaskStatusList([{ taskId: "a" }, { taskId: "b" }]);
+    expect(result).toHaveLength(2);
+    expect(result[0].taskId).toBe("a");
+  });
+
+  it("parses an envelope { tasks: [...] }", () => {
+    const result = parseAiTaskStatusList({ tasks: [{ taskId: "a" }, { task_id: "b" }] });
+    expect(result).toHaveLength(2);
+    expect(result[1].taskId).toBe("b");
+  });
+
+  it("parses an envelope { items: [...] }", () => {
+    const result = parseAiTaskStatusList({ items: [{ taskId: "a" }] });
+    expect(result).toHaveLength(1);
+  });
+
+  it("drops rows with no taskId rather than crashing", () => {
+    const result = parseAiTaskStatusList([{ taskId: "keep" }, { status: "running" }, {}]);
+    expect(result).toHaveLength(1);
+    expect(result[0].taskId).toBe("keep");
+  });
+
+  it("returns empty array for non-array non-record payload", () => {
+    expect(parseAiTaskStatusList(null)).toEqual([]);
+    expect(parseAiTaskStatusList("nope")).toEqual([]);
+    expect(parseAiTaskStatusList({})).toEqual([]);
+  });
+});
+
+describe("parseSseTaskFrame", () => {
+  it("parses a well-formed SSE frame", () => {
+    const frame = parseSseTaskFrame({
+      taskId: "sse-1",
+      status: "completed",
+      progress: 100,
+      resultUrl: "https://example.com/done.png",
+    });
+    expect(frame.taskId).toBe("sse-1");
+    expect(frame.status).toBe("completed");
+    expect(frame.progress).toBe(100);
+    expect(frame.resultUrl).toBe("https://example.com/done.png");
+  });
+
+  it("clamps progress and rejects unknown status", () => {
+    const frame = parseSseTaskFrame({ taskId: "sse-2", status: "oops", progress: 999 });
+    expect(frame.status).toBe("failed");
+    expect(frame.progress).toBe(100);
+  });
+
+  it("handles a non-object payload", () => {
+    const frame = parseSseTaskFrame("garbage");
+    expect(frame.taskId).toBe("");
+    expect(frame.status).toBe("failed");
+    expect(frame.progress).toBe(0);
+  });
+});
diff --git a/src/api/dtoParsers.ts b/src/api/dtoParsers.ts
new file mode 100644
index 0000000..66d3a03
--- /dev/null
+++ b/src/api/dtoParsers.ts
@@ -0,0 +1,173 @@
+// DTO 解析层：把后端返回的 unknown 安全地解析成强类型 view model。
+// 所有从 serverRequest / SSE / localStorage 进入前端状态的 DTO 都应经过这里的 parser，
+// 避免 as unknown as / as T 这类静默断言在后端变形时把 undefined/错误类型传到 UI。
+//
+// helper 与 keyServerClient 里的 toNumber/toStringValue 同构，为避免改动 keyServerClient
+// 暂在此自带一份；后续可统一到共享 dtoHelpers 模块。
+
+import { isRecord } from "./serverConnection";
+import type { AiTaskStatus, ImageTaskCreateResponse, ImageProviderDebug } from "./aiGenerationClient";
+
+function toNumber(value: unknown, fallback = 0): number {
+  const numberValue = typeof value === "number" ? value : Number(value);
+  return Number.isFinite(numberValue) ? numberValue : fallback;
+}
+
+function toNullableString(value: unknown): string | null {
+  if (typeof value !== "string") return null;
+  const trimmed = value.trim();
+  return trimmed || null;
+}
+
+const TASK_STATUS_VALUES: ReadonlySet<string> = new Set(["pending", "running", "completed", "failed", "cancelled"]);
+const TASK_TYPE_VALUES: ReadonlySet<string> = new Set(["image", "video"]);
+
+function normalizeTaskStatusValue(value: unknown): AiTaskStatus["status"] {
+  return typeof value === "string" && TASK_STATUS_VALUES.has(value)
+    ? (value as AiTaskStatus["status"])
+    : "failed";
+}
+
+function normalizeTaskTypeValue(value: unknown): AiTaskStatus["type"] {
+  return typeof value === "string" && TASK_TYPE_VALUES.has(value) ? (value as AiTaskStatus["type"]) : "image";
+}
+
+interface ProviderDebugCandidate {
+  provider?: string;
+  transport?: string;
+  model?: string;
+  requestedModel?: string;
+  billingProvider?: string;
+  fallbackOf?: string;
+}
+
+function normalizeProviderDebugCandidate(raw: unknown): ProviderDebugCandidate {
+  if (!isRecord(raw)) return {};
+  return {
+    provider: toNullableString(raw.provider) ?? undefined,
+    transport: toNullableString(raw.transport) ?? undefined,
+    model: toNullableString(raw.model) ?? undefined,
+    requestedModel: toNullableString(raw.requestedModel ?? raw.requested_model) ?? undefined,
+    billingProvider: toNullableString(raw.billingProvider ?? raw.billing_provider) ?? undefined,
+    fallbackOf: toNullableString(raw.fallbackOf ?? raw.fallback_of) ?? undefined,
+  };
+}
+
+function toStringArray(raw: unknown): string[] | undefined {
+  if (!Array.isArray(raw)) return undefined;
+  return (raw as unknown[])
+    .map((item) => toNullableString(item))
+    .filter((item): item is string => item !== null);
+}
+
+function normalizeProviderDebug(raw: unknown): ImageProviderDebug | undefined {
+  if (!isRecord(raw)) return undefined;
+  const hasAny =
+    (raw.requestedModel ?? raw.requested_model) !== undefined ||
+    (raw.effectiveModel ?? raw.effective_model) !== undefined ||
+    (raw.primaryProvider ?? raw.primary_provider) !== undefined ||
+    (raw.fallbackProviders ?? raw.fallback_providers) !== undefined ||
+    raw.route !== undefined ||
+    raw.candidates !== undefined;
+  if (!hasAny) return undefined;
+  const fallbackProviders = toStringArray(raw.fallbackProviders ?? raw.fallback_providers);
+  const route = toStringArray(raw.route);
+  const candidates = Array.isArray(raw.candidates)
+    ? (raw.candidates as unknown[]).map(normalizeProviderDebugCandidate)
+    : undefined;
+  return {
+    requestedModel: toNullableString(raw.requestedModel ?? raw.requested_model) ?? undefined,
+    effectiveModel: toNullableString(raw.effectiveModel ?? raw.effective_model) ?? undefined,
+    primaryProvider: toNullableString(raw.primaryProvider ?? raw.primary_provider) ?? undefined,
+    fallbackProviders,
+    route,
+    candidates,
+  };
+}
+
+/**
+ * Parse a single task status DTO. Returns a well-formed AiTaskStatus with safe
+ * defaults for any missing/malformed field, so downstream code never sees
+ * undefined where it expects a value.
+ */
+export function parseAiTaskStatus(payload: unknown): AiTaskStatus {
+  const task = isRecord(payload) ? payload : {};
+  return {
+    taskId: toNullableString(task.taskId ?? task.task_id ?? task.id) ?? "",
+    projectId: toNullableString(task.projectId ?? task.project_id) ?? undefined,
+    conversationId: typeof task.conversationId === "number" || typeof task.conversation_id === "number"
+      ? ((task.conversationId ?? task.conversation_id) as number)
+      : null,
+    clientQueueId: toNullableString(task.clientQueueId ?? task.client_queue_id),
+    type: normalizeTaskTypeValue(task.type),
+    status: normalizeTaskStatusValue(task.status),
+    progress: Math.max(0, Math.min(100, toNumber(task.progress))),
+    resultUrl: toNullableString(task.resultUrl ?? task.result_url),
+    error: toNullableString(task.error),
+    params: isRecord(task.params) ? task.params : undefined,
+    createdAt: toNullableString(task.createdAt ?? task.created_at) ?? "",
+    updatedAt: toNullableString(task.updatedAt ?? task.updated_at) ?? "",
+    completedAt: toNullableString(task.completedAt ?? task.completed_at),
+  };
+}
+
+/**
+ * Parse a task-create response ({ taskId }). Throws if taskId is missing,
+ * rather than silently returning { taskId: undefined }.
+ */
+export function parseTaskCreateResponse(payload: unknown): { taskId: string } {
+  const body = isRecord(payload) ? payload : {};
+  const taskId = toNullableString(body.taskId ?? body.task_id ?? body.id);
+  if (!taskId) {
+    throw new Error("任务创建失败：服务端未返回任务 ID");
+  }
+  return { taskId };
+}
+
+/**
+ * Parse an image task-create response, including optional provider debug info.
+ */
+export function parseImageTaskCreateResponse(payload: unknown): ImageTaskCreateResponse {
+  const base = parseTaskCreateResponse(payload);
+  const body = isRecord(payload) ? payload : {};
+  const providerDebug = normalizeProviderDebug(body.providerDebug ?? body.provider_debug);
+  return providerDebug ? { ...base, providerDebug } : base;
+}
+
+/**
+ * Parse a task list payload that may be a bare array or an envelope
+ * ({ tasks | items: [...] }). Malformed elements are dropped, not coerced,
+ * because a single bad row should not corrupt the whole history list.
+ */
+export function parseAiTaskStatusList(payload: unknown): AiTaskStatus[] {
+  let rows: unknown[];
+  if (Array.isArray(payload)) {
+    rows = payload;
+  } else if (isRecord(payload)) {
+    const nested = payload.tasks ?? payload.items;
+    rows = Array.isArray(nested) ? nested : [];
+  } else {
+    rows = [];
+  }
+  // Keep only rows that have a non-empty taskId — empty-id rows are useless
+  // to the UI and indicate a malformed DTO.
+  return rows.map(parseAiTaskStatus).filter((task) => task.taskId);
+}
+
+/**
+ * Parse an SSE task frame. SSE data is untyped JSON from the server stream;
+ * this validates the subset of fields that subscribeTaskStatus forwards.
+ */
+export function parseSseTaskFrame(payload: unknown): Pick<
+  AiTaskStatus,
+  "taskId" | "status" | "progress" | "resultUrl" | "error"
+> {
+  const frame = isRecord(payload) ? payload : {};
+  return {
+    taskId: toNullableString(frame.taskId ?? frame.task_id) ?? "",
+    status: normalizeTaskStatusValue(frame.status),
+    progress: Math.max(0, Math.min(100, toNumber(frame.progress))),
+    resultUrl: toNullableString(frame.resultUrl ?? frame.result_url),
+    error: toNullableString(frame.error),
+  };
+}
diff --git a/src/api/serverConnection.ts b/src/api/serverConnection.ts
index 2316f72..78f5650 100644
--- a/src/api/serverConnection.ts
+++ b/src/api/serverConnection.ts
@@ -82,9 +82,19 @@ function parseStoredSession(raw: string | null): WebUserSession | null {
 
   try {
     const parsed = JSON.parse(raw) as unknown;
-    return isRecord(parsed) && typeof parsed.token === "string" && isRecord(parsed.user)
-      ? (parsed as unknown as WebUserSession)
-      : null;
+    // Require token + a user object with at least an id, so a malformed/partial
+    // cached session does not get cast wholesale into WebUserSession and then
+    // crash UI code that reads user.id / user.username.
+    if (!isRecord(parsed) || typeof parsed.token !== "string" || !isRecord(parsed.user)) {
+      return null;
+    }
+    const user = parsed.user;
+    const userId = user.id ?? user.userId ?? user.user_id;
+    const username = user.username ?? user.name;
+    if (userId === undefined || typeof username !== "string" || !username.trim()) {
+      return null;
+    }
+    return parsed as unknown as WebUserSession;
   } catch {
     return null;
   }