fix: poll for preview results to avoid undici headers timeout (#8682)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cli/src/commands/flow/flow.ts

@@ -15,7 +15,7 @@ import { buildFolderPath, getMetadataFileName, loadNonDottedPathsSetting } from
 
 import { requireLogin } from "../../core/auth.ts";
 import { resolveWorkspace, validatePath } from "../../core/context.ts";
-import { resolve, track_job } from "../script/script.ts";
+import { resolve, track_job, pollForJobResult } from "../script/script.ts";
 import { defaultFlowDefinition } from "../../../bootstrap/flow_bootstrap.ts";
 import { SyncOptions, mergeConfigWithConfigFile } from "../../core/conf.ts";
 import { FSFSElement, elementsToMap, ignoreF } from "../sync/sync.ts";
@@ -574,32 +574,27 @@ async function preview(
 
   log.debug(`Flow value: ${JSON.stringify(localFlow.value, null, 2)}`);
 
-  // Run the flow preview
-  let result;
-  try {
-    result = await wmill.runFlowPreviewAndWaitResult({
-      workspace: workspace.workspaceId,
-      requestBody: {
-        value: localFlow.value,
-        path: flowPath.substring(0, flowPath.indexOf(".flow")).replaceAll(SEP, "/"),
-        args: input,
-      },
-    });
-  } catch (e: any) {
-    if (e.body) {
-      // If a failure_module ran, the body contains its result — not an error
-      if (e.body.result !== undefined) {
-        if (opts.silent) {
-          console.log(JSON.stringify(e.body.result));
-        } else {
-          log.info(colors.yellow.bold("Flow failed, error handler result:"));
-          log.info(JSON.stringify(e.body.result, null, 2));
-        }
-        process.exitCode = 1;
-        return;
-      }
+  // Run the flow preview — start the job, then poll for completion
+  const jobId = await wmill.runFlowPreview({
+    workspace: workspace.workspaceId,
+    requestBody: {
+      value: localFlow.value,
+      path: flowPath.substring(0, flowPath.indexOf(".flow")).replaceAll(SEP, "/"),
+      args: input,
+    },
+  });
+
+  const { result, success } = await pollForJobResult(workspace.workspaceId, jobId);
+
+  if (!success) {
+    if (opts.silent) {
+      console.log(JSON.stringify(result));
+    } else {
+      log.info(colors.yellow.bold("Flow failed, error handler result:"));
+      log.info(JSON.stringify(result, null, 2));
     }
-    throw e;
+    process.exitCode = 1;
+    return;
   }
 
   if (opts.silent) {

cli/src/commands/script/script.ts

@@ -1118,6 +1118,27 @@ export async function track_job(workspace: string, id: string) {
   }
 }
 
+const POLL_INTERVAL_MS = 2000;
+
+export async function pollForJobResult(
+  workspace: string,
+  jobId: string,
+): Promise<{ result: unknown; success: boolean }> {
+  while (true) {
+    const maybeResult = await wmill.getCompletedJobResultMaybe({
+      workspace,
+      id: jobId,
+      getStarted: false,
+    });
+
+    if (maybeResult.completed) {
+      return { result: maybeResult.result, success: maybeResult.success ?? false };
+    }
+
+    await new Promise((resolve) => setTimeout(resolve, POLL_INTERVAL_MS));
+  }
+}
+
 async function show(opts: GlobalOptions, path: string) {
   const workspace = await resolveWorkspace(opts);
   await requireLogin(opts);
@@ -1532,8 +1553,8 @@ async function preview(
       }
     }
   } else {
-    // For regular scripts, use the standard preview API
-    const result = await wmill.runScriptPreviewAndWaitResult({
+    // For regular scripts, start the preview job then poll for completion
+    const jobId = await wmill.runScriptPreview({
       workspace: workspace.workspaceId,
       requestBody: {
         content,
@@ -1544,8 +1565,21 @@ async function preview(
       },
     });
 
+    const { result, success } = await pollForJobResult(workspace.workspaceId, jobId);
+
+    if (!success) {
+      if (opts.silent) {
+        console.log(JSON.stringify(result));
+      } else {
+        log.info(colors.red.bold("Preview failed"));
+        log.info(JSON.stringify(result, null, 2));
+      }
+      process.exitCode = 1;
+      return;
+    }
+
     if (opts.silent) {
-      console.log(JSON.stringify(result, null, 2));
+      console.log(JSON.stringify(result));
     } else {
       log.info(colors.bold.underline.green("Preview completed"));
       log.info(JSON.stringify(result, null, 2));