fix: S3→Telegram upload pipeline — OOM, queue limits, shutdown drain, timeouts

CRITICAL:
- Content-MD5 no longer loads entire file via arrayBuffer() — MD5 computed
  incrementally in streamBodyToTemp alongside SHA-256 (fixes OOM for GB files)

HIGH:
- Add 120s timeout to Telegraf API calls via Promise.race in executeWithBotRetry
  (prevents queue slot exhaustion from hung Telegram connections)
- Add queue size limit (1000 pending max) — reject new tasks when full
- Add graceful shutdown drain — waitForQueue with 30s timeout before exit
- Fix temp file leak when findFileByBucketAndKey throws (wrap in try-catch)
- Fix createReadStream fd leak — destroy stream on forwardToStorage error
- writer.end() wrapped in silent try-catch to prevent error swallowing
- writer.end() result ignored, writerFailed flag prevents double-end

MEDIUM:
- Remove 'retry after' from isTransientError patterns to stop double-retry
  layering (was causing up to 96 bot attempts per chunk)

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/infrastructure/telegram/bot-pool.ts

@@ -42,7 +42,9 @@ const sleep = (ms: number): Promise<void> => {
 const isTransientError = (error: unknown): boolean => {
   const str = error instanceof Error ? error.message : String(error);
   const transientPatterns = [
-    'retry after',
+    // 'retry after' is deliberately omitted — 429 is handled by
+    // executeWithBotRetry at a deeper layer. Including it here would
+    // cause double-retry (up to 96 attempts per chunk).
     'timeout',
     'Timed out',
     'etimedout',
@@ -76,6 +78,12 @@ const isTransientError = (error: unknown): boolean => {
  */
 const MAX_TRANSIENT_RETRIES = 3;
 
+/**
+ * Timeout in milliseconds for individual Telegram API calls.
+ * 120 seconds to accommodate large document uploads.
+ */
+const TELEGRAM_API_TIMEOUT_MS = 120_000;
+
 /**
  * Manages a pool of Telegram bots with automatic rotation and rate-limit handling.
  *
@@ -129,7 +137,17 @@ export class BotPool implements ITelegramService {
     const currentBot = this.bots[botIndex];
     const currentToken = this.botTokens[botIndex];
     try {
-      return await action(currentBot, currentToken);
+      // Add timeout to prevent hung API calls from occupying queue slots
+      const result = await Promise.race([
+        action(currentBot, currentToken),
+        new Promise<never>((_, reject) =>
+          setTimeout(
+            () => reject(new Error(`Telegram API timeout after ${TELEGRAM_API_TIMEOUT_MS}ms`)),
+            TELEGRAM_API_TIMEOUT_MS,
+          ),
+        ),
+      ]);
+      return result;
     } catch (error: unknown) {
       const errorStr = error instanceof Error ? error.message : String(error);
       const match = errorStr.match(/retry after (\d+)/i);

src/infrastructure/telegram/upload-queue.ts

@@ -2,6 +2,13 @@ import PQueue from 'p-queue';
 import { config } from '../../env';
 import logger from '../../shared/logger/index';
 
+/**
+ * Maximum number of pending (queued + in-flight) upload tasks before
+ * new submissions are rejected. Prevents unbounded memory growth when
+ * Telegram is slow or unavailable.
+ */
+const MAX_QUEUE_PENDING = 1000;
+
 /**
  * P-queue instance for serialising Telegram upload tasks.
  *
@@ -16,7 +23,11 @@ const uploadQueue = new PQueue({
 uploadQueue.on('add', () => {
   const stats = getQueueStats();
   if (stats.size > 5) {
-    logger.warn('Upload queue building up', { pending: stats.pending, size: stats.size });
+    logger.warn('Upload queue building up', {
+      pending: stats.pending,
+      size: stats.size,
+      max: MAX_QUEUE_PENDING,
+    });
   }
 });
 
@@ -34,6 +45,14 @@ uploadQueue.on('next', () => {
  * @returns A promise that resolves with the task's result.
  */
 export const enqueueUpload = <T>(task: () => Promise<T>): Promise<T> => {
+  const stats = getQueueStats();
+  if (stats.pending + stats.size > MAX_QUEUE_PENDING) {
+    return Promise.reject(
+      new Error(
+        `Upload queue full (${stats.pending + stats.size} pending, max ${MAX_QUEUE_PENDING})`,
+      ),
+    );
+  }
   return uploadQueue.add(task);
 };