diff --git a/worker/src/archive/split.ts b/worker/src/archive/split.ts
index 17d6401..f427da9 100644
--- a/worker/src/archive/split.ts
+++ b/worker/src/archive/split.ts
@@ -6,8 +6,12 @@ import { childLogger } from "../util/logger.js";
 
 const log = childLogger("split");
 
-/** 2GB in bytes — Telegram's file size limit */
-const MAX_PART_SIZE = 2n * 1024n * 1024n * 1024n;
+/**
+ * 1950 MiB — safely under Telegram's 2GB upload limit.
+ * At exactly 2GiB, TDLib's internal 512KB chunking can exceed Telegram's
+ * 4000-part threshold, causing FILE_PARTS_INVALID errors.
+ */
+const MAX_PART_SIZE = 1950n * 1024n * 1024n;
 
 /**
  * Split a file into ≤2GB parts using byte-level splitting.
diff --git a/worker/src/tdlib/download.ts b/worker/src/tdlib/download.ts
index 336a83b..e96e07d 100644
--- a/worker/src/tdlib/download.ts
+++ b/worker/src/tdlib/download.ts
@@ -353,11 +353,14 @@ export async function downloadFile(
   return new Promise<void>((resolve, reject) => {
     let lastLoggedPercent = 0;
     let settled = false;
+    let downloadStarted = false; // True once TDLib reports is_downloading_active
+    let lastProgressBytes = 0;
+    let lastProgressTime = Date.now();
 
-    // Timeout: 15 minutes per GB, minimum 10 minutes
+    // Timeout: 20 minutes per GB, minimum 15 minutes
     const timeoutMs = Math.max(
-      10 * 60_000,
-      (totalBytes / (1024 * 1024 * 1024)) * 15 * 60_000
+      15 * 60_000,
+      (totalBytes / (1024 * 1024 * 1024)) * 20 * 60_000
     );
     const timer = setTimeout(() => {
       if (!settled) {
@@ -371,6 +374,23 @@ export async function downloadFile(
       }
     }, timeoutMs);
 
+    // Stall detection: no progress for 5 minutes after download started → reject
+    const STALL_TIMEOUT_MS = 5 * 60_000;
+    const stallChecker = setInterval(() => {
+      if (settled || !downloadStarted) return;
+      const stallMs = Date.now() - lastProgressTime;
+      if (stallMs >= STALL_TIMEOUT_MS) {
+        settled = true;
+        cleanup();
+        reject(
+          new Error(
+            `Download stalled for ${fileName} — no progress for ${Math.round(stallMs / 60_000)}min ` +
+              `(${lastProgressBytes}/${totalBytes} bytes)`
+          )
+        );
+      }
+    }, 30_000);
+
     // Listen for file update events to track progress
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     const handleUpdate = (update: any) => {
@@ -382,6 +402,17 @@ export async function downloadFile(
       const percent =
         totalBytes > 0 ? Math.round((downloaded / totalBytes) * 100) : 0;
 
+      // Track whether the download has actually started
+      if (file.local.is_downloading_active) {
+        downloadStarted = true;
+      }
+
+      // Reset stall timer when bytes advance
+      if (downloaded > lastProgressBytes) {
+        lastProgressBytes = downloaded;
+        lastProgressTime = Date.now();
+      }
+
       // Log at every 10% increment
       if (percent >= lastLoggedPercent + 10) {
         lastLoggedPercent = percent - (percent % 10);
@@ -412,8 +443,11 @@ export async function downloadFile(
         }
       }
 
-      // Download stopped without completing (network error, cancelled, etc.)
+      // Download stopped without completing — only if it had actually started.
+      // TDLib may emit an initial updateFile with is_downloading_active=false
+      // before the download begins; ignoring that prevents false positives.
       if (
+        downloadStarted &&
         !file.local.is_downloading_active &&
         !file.local.is_downloading_completed
       ) {
@@ -432,6 +466,7 @@ export async function downloadFile(
 
     const cleanup = () => {
       clearTimeout(timer);
+      clearInterval(stallChecker);
       client.off("update", handleUpdate);
     };
 
diff --git a/worker/src/upload/channel.ts b/worker/src/upload/channel.ts
index e019d33..fd6212f 100644
--- a/worker/src/upload/channel.ts
+++ b/worker/src/upload/channel.ts
@@ -93,11 +93,13 @@ async function sendAndWaitForUpload(
     let settled = false;
     let lastLoggedPercent = 0;
     let tempMsgId: number | null = null;
+    let uploadStarted = false;
+    let lastProgressTime = Date.now();
 
-    // Timeout: 15 minutes per GB, minimum 10 minutes
+    // Timeout: 20 minutes per GB, minimum 15 minutes
     const timeoutMs = Math.max(
-      10 * 60_000,
-      (fileSizeMB / 1024) * 15 * 60_000
+      15 * 60_000,
+      (fileSizeMB / 1024) * 20 * 60_000
     );
 
     const timer = setTimeout(() => {
@@ -112,12 +114,31 @@ async function sendAndWaitForUpload(
       }
     }, timeoutMs);
 
+    // Stall detection: no progress for 5 minutes after upload started → reject
+    const STALL_TIMEOUT_MS = 5 * 60_000;
+    const stallChecker = setInterval(() => {
+      if (settled || !uploadStarted) return;
+      const stallMs = Date.now() - lastProgressTime;
+      if (stallMs >= STALL_TIMEOUT_MS) {
+        settled = true;
+        cleanup();
+        reject(
+          new Error(
+            `Upload stalled for ${fileName} — no progress for ${Math.round(stallMs / 60_000)}min`
+          )
+        );
+      }
+    }, 30_000);
+
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     const handleUpdate = (update: any) => {
       // Track upload progress via updateFile events
       if (update?._ === "updateFile") {
         const file = update.file;
         if (file?.remote?.is_uploading_active && file.expected_size > 0) {
+          uploadStarted = true;
+          lastProgressTime = Date.now();
+
           const uploaded = file.remote.uploaded_size ?? 0;
           const total = file.expected_size;
           const percent = Math.round((uploaded / total) * 100);
@@ -165,6 +186,7 @@ async function sendAndWaitForUpload(
 
     const cleanup = () => {
       clearTimeout(timer);
+      clearInterval(stallChecker);
       client.off("update", handleUpdate);
     };
 
diff --git a/worker/src/worker.ts b/worker/src/worker.ts
index f028132..37d134e 100644
--- a/worker/src/worker.ts
+++ b/worker/src/worker.ts
@@ -999,7 +999,7 @@ async function processOneArchiveSet(
       (sum, p) => sum + p.fileSize,
       0n
     );
-    const MAX_UPLOAD_SIZE = 2n * 1024n * 1024n * 1024n;
+    const MAX_UPLOAD_SIZE = 1950n * 1024n * 1024n; // Match split.ts MAX_PART_SIZE
     const hasOversizedPart = archiveSet.parts.some((p) => p.fileSize > MAX_UPLOAD_SIZE);
 
     if (hasOversizedPart) {