feat(gateway): implement separate Piscina pools for text and media analysis to optimize processing

services/discord-gateway/src/modules/ai-moderation/circuitBreaker.ts

@@ -6,7 +6,16 @@ import { config } from "../../shared/config/config.js";
 import type { MessageRecord } from "../message-capture/types.js";
 
 // ---------------------------------------------------------------------------
-// Piscina worker pool (shared by batch + individual pipelines)
+// Piscina worker pools (2026-08-31: split text vs media)
+//
+// Both the batch and individual-fallback pipelines used to share ONE pool.
+// A conversation batch containing images/stickers/embeds routes through
+// runMediaBatch (download + vision + LLM — tens of seconds per batch), and
+// Piscina hands each worker thread exactly one task at a time. With a small
+// fixed thread count, a handful of slow media batches could occupy every
+// thread and leave fast text-only batches for OTHER conversations queued
+// behind them for the whole media duration. Text and media now get their
+// own dedicated pools so a media backlog can never starve text analysis.
 // ---------------------------------------------------------------------------
 
 function getAnalysisWorkerUrl(): URL {
@@ -25,12 +34,32 @@ function getAnalysisWorkerUrl(): URL {
   return candidates[2];
 }
 
-export const workerPool = new Piscina({
-  filename: fileURLToPath(getAnalysisWorkerUrl()),
+const analysisWorkerFilename = fileURLToPath(getAnalysisWorkerUrl());
+
+/** Dedicated pool for text-only batch/individual analysis jobs. */
+export const textWorkerPool = new Piscina({
+  filename: analysisWorkerFilename,
   execArgv: process.execArgv,
   maxThreads: config.PISCINA_MAX_THREADS ?? availableParallelism(),
 });
 
+/**
+ * Dedicated pool for jobs whose batch contains at least one message with
+ * media (attachments/stickers/embeds). Kept separate so slow image/vision
+ * analysis never blocks the text pool above.
+ */
+export const mediaWorkerPool = new Piscina({
+  filename: analysisWorkerFilename,
+  execArgv: process.execArgv,
+  maxThreads: config.PISCINA_MEDIA_MAX_THREADS ?? 2,
+});
+
+/**
+ * @deprecated Use `textWorkerPool` or `mediaWorkerPool` directly. Kept as an
+ * alias to the text pool only for anything not yet migrated.
+ */
+export const workerPool = textWorkerPool;
+
 /**
  * Gets the conversation key for a message (thread_id or channel_id).
  */