feat(update): show stderr for failed steps

src/cli/update-cli.ts

@@ -64,6 +64,15 @@ function createUpdateProgress(enabled: boolean): ProgressController {
 
       currentSpinner.stop(`${icon} ${label} ${duration}`);
       currentSpinner = null;
+
+      if (step.exitCode !== 0 && step.stderrTail) {
+        const lines = step.stderrTail.split("\n").slice(-10);
+        for (const line of lines) {
+          if (line.trim()) {
+            defaultRuntime.log(`    ${theme.error(line)}`);
+          }
+        }
+      }
     },
   };
 

src/infra/update-runner.ts

@@ -40,6 +40,7 @@ export type UpdateStepInfo = {
 export type UpdateStepCompletion = UpdateStepInfo & {
   durationMs: number;
   exitCode: number | null;
+  stderrTail?: string | null;
 };
 
 export type UpdateStepProgress = {
@@ -199,10 +200,13 @@ async function runStep(opts: RunStepOptions): Promise<UpdateStepResult> {
   const result = await runCommand(argv, { cwd, timeoutMs, env });
   const durationMs = Date.now() - started;
 
+  const stderrTail = trimLogTail(result.stderr, MAX_LOG_CHARS);
+
   progress?.onStepComplete?.({
     ...stepInfo,
     durationMs,
     exitCode: result.code,
+    stderrTail,
   });
 
   return {