fix: stabilize ssh artifact downloads

scripts/src/ssh-file-transfer.ts

@@ -53,7 +53,9 @@ class SshFileTransferError extends Error {
 const fileTransferReadBlockBytes = 45_000;
 const fileTransferWriteB64ArgvLimit = 48_000;
 const fileTransferWriteB64ChunkChars = 12_000;
-const fileTransferReadBlockMaxAttempts = 3;
+const fileTransferReadBlockMaxAttempts = 12;
+const fileTransferReadEmptyRetryDelayMs = 250;
+const fileTransferProgressEveryChunks = 64;
 
 export function isSshFileTransferOperation(args: string[]): boolean {
   const subcommand = args[0] ?? "";
@@ -210,6 +212,7 @@ async function readRemoteFileVerified(
     chunks.push(chunk);
     actualBytes += chunk.length;
     chunkCount += 1;
+    emitDownloadProgress(invocation, remotePath, blockIndex, chunkCount, actualBytes, remote.bytes, chunk.length);
   }
   const content = Buffer.concat(chunks);
   const actual = { bytes: content.length, sha256: sha256HexBuffer(content) };
@@ -234,11 +237,19 @@ async function readRemoteBase64BlockWithRetry(
       const encoded = read.stdout.replace(/\s+/gu, "");
       if (encoded.length > 0) return encoded;
       attemptErrors.push({ attempt, exitCode: read.exitCode, stdoutBytes: read.stdout.length, stderrTail: read.stderr.slice(-500) });
+      if (attempt < fileTransferReadBlockMaxAttempts) {
+        emitEmptyReadRetryProgress(invocation, remotePath, blockIndex, attempt, expectedBytes, actualBytes);
+        await delayMs(fileTransferReadEmptyRetryDelayMs);
+      }
     } catch (error) {
       attemptErrors.push({
         attempt,
         error: error instanceof Error ? error.message : String(error),
       });
+      if (attempt < fileTransferReadBlockMaxAttempts) {
+        emitEmptyReadRetryProgress(invocation, remotePath, blockIndex, attempt, expectedBytes, actualBytes);
+        await delayMs(fileTransferReadEmptyRetryDelayMs);
+      }
     }
   }
   throw new SshFileTransferError("remote download returned an empty block before EOF after retries", {
@@ -252,6 +263,54 @@ async function readRemoteBase64BlockWithRetry(
   });
 }
 
+function emitDownloadProgress(
+  invocation: ParsedSshInvocation,
+  remotePath: string,
+  blockIndex: number,
+  chunkCount: number,
+  actualBytes: number,
+  expectedBytes: number,
+  lastChunkBytes: number,
+): void {
+  if (chunkCount !== 1 && actualBytes < expectedBytes && chunkCount % fileTransferProgressEveryChunks !== 0) return;
+  process.stderr.write(`${JSON.stringify({
+    event: "unidesk.ssh.download.progress",
+    route: invocation.route.raw,
+    providerId: invocation.providerId,
+    remotePath,
+    blockIndex,
+    chunks: chunkCount,
+    actualBytes,
+    expectedBytes,
+    lastChunkBytes,
+  })}\n`);
+}
+
+function emitEmptyReadRetryProgress(
+  invocation: ParsedSshInvocation,
+  remotePath: string,
+  blockIndex: number,
+  attempt: number,
+  expectedBytes: number,
+  actualBytes: number,
+): void {
+  process.stderr.write(`${JSON.stringify({
+    event: "unidesk.ssh.download.empty-read-retry",
+    route: invocation.route.raw,
+    providerId: invocation.providerId,
+    remotePath,
+    blockIndex,
+    attempt,
+    maxAttempts: fileTransferReadBlockMaxAttempts,
+    actualBytes,
+    expectedBytes,
+  })}\n`);
+}
+
+function delayMs(ms: number): Promise<void> {
+  return new Promise((resolve) => setTimeout(resolve, ms));
+}
+
 async function statRemoteFile(
   invocation: ParsedSshInvocation,
   executor: SshRemoteCommandExecutor,