fix(web): SSE 重连 401/404 fail-fast，单帧解析容错（R-7）

TaskRunHttpError 携带 status；非法 JSON 帧跳过并保留 seq。

Co-authored-by: Cursor <cursoragent@cursor.com>

web/src/api/taskRuns.ts

@@ -37,6 +37,19 @@ export function sleepMs(ms: number): Promise<void> {
   return new Promise((resolve) => setTimeout(resolve, ms));
 }
 
+export class TaskRunHttpError extends Error {
+  status: number;
+  constructor(status: number) {
+    super(`subscribe task run failed: HTTP ${status}`);
+    this.name = 'TaskRunHttpError';
+    this.status = status;
+  }
+}
+
+function isNonRetryableStatus(status: number): boolean {
+  return status === 401 || status === 404;
+}
+
 /** 单次 SSE 读取；意外 EOF 时返回 { terminal:false, lastSeq } 供上层重连。 */
 export async function readTaskRunSSEOnce(
   runId: string,
@@ -51,7 +64,7 @@ export async function readTaskRunSSEOnce(
     signal,
   });
   if (!resp.ok || !resp.body) {
-    throw new Error(`subscribe task run failed: HTTP ${resp.status}`);
+    throw new TaskRunHttpError(resp.status);
   }
   const reader = resp.body.getReader();
   const decoder = new TextDecoder();
@@ -113,6 +126,9 @@ export async function subscribeTaskRunEvents(
       // 意外 EOF：未见到 done/error，按 after_seq 重连
     } catch (err) {
       if (signal?.aborted) return;
+      if (err instanceof TaskRunHttpError && isNonRetryableStatus(err.status)) {
+        throw err;
+      }
       if (attempt >= maxReconnects) throw err;
     }
     if (attempt >= maxReconnects) {