style(gateway,backend): clear all biome warnings (no warnings left behind)

Address every remaining biome lint/format warning across both services
so the codebase ships warning-free:

- textCacheStore: drop unused deleteExpiredQdrantPoints import; hash
  image cache key (sha256[:32]) so long/base64 URLs no longer blow the
  text_analysis_cache PK B-tree 8191-byte index (was aborting the media
  analysis lock INSERT).
- bootstrap: drop unused unhandledRejection promise param.
- moderationOrchestrator: drop unused  destructure at L197.
- mediaDownloader / textBatchProcessor / transmitter: replace non-null
  assertions with proper null guards (stickerName ?? '', urlImages.get
  guard, backpressureQueue.shift guard).
- backend utils: throw lastError ?? fallback instead of lastError!.
- message-capture: remove unused  (retentionDb),  (moderationActionsDb,
  reviewsDb); simplify renderDiscordMentions guard to optional chain.
- transmitter: remove dead write-only  field + its assignments.

No behavior change beyond the cache-key hashing (now deterministic
fixed-length) and the intentional null-safety guards.

services/backend/src/shared/utils/index.ts

@@ -108,5 +108,5 @@ export async function retryWithBackoff<T>(
       });
     }
   }
-  throw lastError!;
+  throw lastError ?? new Error("Request failed after all retries");
 }

services/discord-gateway/src/app/bootstrap.ts

@@ -315,7 +315,7 @@ export async function initializeDiscordGateway() {
     gracefulShutdown("uncaughtException");
   });
 
-  process.on("unhandledRejection", (reason, promise) => {
+  process.on("unhandledRejection", (reason) => {
     const err =
       reason instanceof Error ? reason : new Error(String(reason ?? "unknown"));
     const code = (err as NodeJS.ErrnoException).code ?? "";

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

@@ -450,7 +450,7 @@ export async function downloadMediaCandidate(
   if (candidate.customEmojiId || candidate.stickerName) {
     const vck = candidate.customEmojiId
       ? makeCustomEmojiCacheKey(candidate.customEmojiId)
-      : makeStickerCacheKey(candidate.stickerName!);
+      : makeStickerCacheKey(candidate.stickerName ?? "");
     const cached = await getCachedMediaAnalysis(vck);
     if (cached) {
       const existing = mediaAnalysisMap.get(targetId) ?? [];

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

@@ -194,7 +194,7 @@ export async function runModerationAnalysis(
       if (embeddings && embeddings.length === texts.length) {
         // index-aligned with semanticCandidates
         for (let i = 0; i < semanticCandidates.length; i++) {
-          const { target, cacheKey } = semanticCandidates[i];
+          const { cacheKey } = semanticCandidates[i];
           embeddingsByKey.set(cacheKey, embeddings[i]);
         }
 

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

@@ -249,7 +249,8 @@ export async function runTextOnlyBatch(
           if (pics.length === 0) return { id: msg.id, lines: [] as string[] };
           const lines = await Promise.all(
             pics.map(async (url) => {
-              const img = urlImages.get(url)!;
+              const img = urlImages.get(url);
+              if (!img) return null;
               try {
                 const { data: resizedBuffer, mimeType: resizedMime } =
                   await resizeImageForVision(img.data, maxDim);

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

@@ -3,7 +3,6 @@ import { createChildLogger } from "@/shared/logger/index";
 import { executeAll, executeGet } from "../../shared/database/drizzle.js";
 import { findBestEmbeddingMatch } from "./embeddingClient.js";
 import {
-  deleteExpiredQdrantPoints,
   deleteQdrantPoint,
   deleteQdrantPointsByContentHash,
   isQdrantConfigured,

services/discord-gateway/src/modules/message-capture/messageMetadata.ts

@@ -515,7 +515,7 @@ export function renderDiscordMentions(
   content: string,
   metadata: string | null | undefined,
 ): string {
-  if (!content || !content.includes("<")) return content;
+  if (!content?.includes("<")) return content;
   const parsed = parseRichMessageMetadata(metadata);
   const roleName = new Map(
     (parsed?.mentionedRoles ?? []).map((r) => [r.id, r.name] as const),

services/discord-gateway/src/modules/message-capture/moderationActionsDb.ts

@@ -1,4 +1,4 @@
-import { and, desc, eq, inArray, type SQL, sql } from "drizzle-orm";
+import { and, desc, eq, inArray, type SQL } from "drizzle-orm";
 import type { NodePgDatabase } from "drizzle-orm/node-postgres";
 import type * as schema from "../../shared/database/schema.js";
 import { moderationActionsTable } from "../../shared/database/schema.js";

services/discord-gateway/src/modules/message-capture/retentionDb.ts

@@ -1,4 +1,4 @@
-import { and, eq, isNull, or } from "drizzle-orm";
+import { and, eq, isNull } from "drizzle-orm";
 import type { NodePgDatabase } from "drizzle-orm/node-postgres";
 import { createChildLogger, type Logger } from "@/shared/logger/index";
 import type * as schema from "../../shared/database/schema.js";

services/discord-gateway/src/modules/message-capture/reviewsDb.ts

@@ -1,4 +1,4 @@
-import { and, desc, eq, inArray, type SQL, sql } from "drizzle-orm";
+import { and, desc, eq, inArray, type SQL } from "drizzle-orm";
 import type { NodePgDatabase } from "drizzle-orm/node-postgres";
 import type * as schema from "../../shared/database/schema.js";
 import { messageReviewsTable } from "../../shared/database/schema.js";

services/discord-gateway/src/modules/voice-recording/transmitter.ts

@@ -27,8 +27,6 @@ export class VoiceTransmitter {
   private gate = Promise.resolve();
   /** Set true before sending SIGTERM so exit handler knows it's intentional */
   private _expectedExit = false;
-  /** True while the underlying stream is in a drain state (backpressure) */
-  private draining = false;
 
   /**
    * Start listening for PCM audio data from Redis and stream to Discord
@@ -179,15 +177,13 @@ export class VoiceTransmitter {
             const canContinue = stream.write(pcmBuffer);
             // Backpressure: queue until drain
             if (!canContinue) {
-              this.draining = true;
               stream.once("drain", () => {
-                this.draining = false;
-                // Re-acquire stream reference (could have been replaced by restart)
                 const currentStream = this.pcmStream;
                 if (!currentStream || !this.isActive) return;
                 // Flush queued chunks
                 while (this.backpressureQueue.length > 0) {
-                  const queued = this.backpressureQueue.shift()!;
+                  const queued = this.backpressureQueue.shift();
+                  if (!queued) break;
                   try {
                     if (!currentStream.write(queued)) break;
                   } catch (err) {
@@ -237,7 +233,6 @@ export class VoiceTransmitter {
       this.isActive = false;
 
       this.backpressureQueue = [];
-      this.draining = false;
 
       if (this.pcmStream) {
         this.pcmStream.removeAllListeners("drain");