fix(cli): stop download tmp cleanup racing the write stream open

packages/cli/src/utils/download.ts

@@ -31,6 +31,20 @@ export function downloadFile(
   const timeoutMs = options.timeoutMs ?? DEFAULT_DOWNLOAD_TIMEOUT_MS;
   return new Promise((resolve, reject) => {
     const follow = (u: string) => {
+      // Set once the 200 branch hands the response to pipeline(). From that
+      // point the pipeline's catch owns BOTH cleanup and rejection: it settles
+      // only after the write stream has closed, so the `.tmp` file provably
+      // exists (or never will) when it unlinks. The request "error" handler
+      // must NOT clean up or reject in that window — createWriteStream opens
+      // asynchronously, so an early unlink+reject races the open and can leave
+      // a stray `.tmp` created AFTER cleanup ran (flaked in CI as
+      // download.test.ts "removes the partial file"; in the wild it strands
+      // partials in the cache dir).
+      let pipelineOwnsCleanup = false;
+      // The request's error (e.g. the timeout message) is more precise than
+      // what the pipeline surfaces for the same failure (destroying the
+      // request can reject the pipeline with a generic premature-close).
+      let requestError: Error | undefined;
       const request = httpsGet(u, (res) => {
         if (res.statusCode === 301 || res.statusCode === 302) {
           const location = res.headers.location;
@@ -46,6 +60,7 @@ export function downloadFile(
           reject(new Error(`Download failed: HTTP ${res.statusCode}`));
           return;
         }
+        pipelineOwnsCleanup = true;
         const file = createWriteStream(tmp);
         pipeline(res, file)
           .then(() => {
@@ -54,13 +69,17 @@ export function downloadFile(
           })
           .catch((err) => {
             removePartialFile(tmp);
-            reject(err);
+            reject(requestError ?? err);
           });
       });
       request.setTimeout(timeoutMs, () => {
         request.destroy(new Error(`Download timed out after ${timeoutMs}ms`));
       });
       request.on("error", (err) => {
+        if (pipelineOwnsCleanup) {
+          requestError = err;
+          return;
+        }
         removePartialFile(tmp);
         reject(err);
       });