fix(gateway): image vision analysis + media cache lock failures

Two root causes behind 'all image analysis failing':

1. imageResizer still emitted lossless PNG for vision input. A 1024px
   Facebook photo balloons to multi-MB PNG base64 that the vision model
   silently rejects ('Vision API null response'). Switch to JPEG q85
   (no upscaling) — same photo drops to ~100-400KB, model processes fine.
   Re-encodes even already-small images so raw originals never bloat the
   data URL. Added tests/imageResizer.test.ts covering both cases.

2. acquireMediaAnalysisLock INSERT aborted with 'index row requires N
   bytes, maximum size is 8191'. text_analysis_cache.text is the PK in a
   B-tree index (8191-byte/row cap); callers pass the raw image URL as the
   key, and base64 data URLs / very long URLs blow past the limit, so the
   lock INSERT fails and every media analysis is skipped. Hash the URL in
   makeImageCacheKey (image:<sha256[:32]>) — fixed-length, deterministic,
   well under the limit. All store/get/lock/delete callers already route
   through this function so lookup stays consistent.

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

@@ -77,14 +77,16 @@ export function makeCustomEmojiCacheKey(emojiId: string): string {
  * (different URLs) never collide.
  */
 export function makeImageCacheKey(imageUrl: string): string {
-  try {
+  // Hash the URL to a fixed-length key. The raw Discord CDN URL is short,
-    const u = new URL(imageUrl);
+  // but callers sometimes pass base64 data URLs (can be multi-MB) or very
-    u.search = "";
+  // long signed/external URLs. text_analysis_cache.text is the PK and lives
-    u.hash = "";
+  // in a B-tree index with an 8191-byte per-row limit — inserting a long URL
-    return `image:${u.toString()}`;
+  // as the key aborts the whole INSERT ("index row requires N bytes, maximum
-  } catch {
+  // size is 8191"), which fails acquireMediaAnalysisLock and silently skips
-    return `image:${imageUrl}`;
+  // every media analysis. A 32-char sha256 keeps the key well under the limit
-  }
+  // and is still deterministic (same attachment → same key).
+  const hash = createHash("sha256").update(imageUrl).digest("hex").slice(0, 32);
+  return `image:${hash}`;
 }
 
 /**

services/discord-gateway/src/modules/attachment-upload/imageResizer.ts

@@ -4,10 +4,17 @@ import { createChildLogger } from "@/shared/logger/index";
 const log = createChildLogger("imageResizer");
 
 /**
- * Prepare an image buffer for optimal vision LLM analysis.
+ * Prepare an image buffer for vision LLM analysis.
  *
- * - Resizes to maxDim x maxDim maintaining aspect ratio (only if larger)
+ * - Resizes to maxDim x maxDim maintaining aspect ratio WITHOUT upscaling
- * - Converts to PNG (lossless) to preserve full image detail
+ *   (small images such as stickers/emojis are passed through at original size,
+ *   just re-encoded)
+ * - Encodes as JPEG (lossy, quality ~85). Photos compress VERY poorly in
+ *   lossless PNG — a 1024px Facebook photo balloons to multi-MB PNG base64 that
+ *   the vision model silently rejects (empty response → "Vision API null").
+ *   JPEG keeps the same photo at ~100–400KB, which the model processes fine and
+ *   stays well below request/token size limits.
+
  * - Falls back to original buffer if sharp fails
  *
  * @param buf - Raw image buffer
@@ -20,35 +27,28 @@ export async function resizeImageForVision(
 ): Promise<{ data: Buffer; mimeType: string }> {
   try {
     const metadata = await sharp(buf).metadata();
-    const inputFormat = metadata.format ?? "jpeg";
 
-    // Skip resize entirely if already within max dimension
+    // Always (re-)encode to JPEG and fit inside maxDim without upscaling.
-    if ((metadata.width ?? 0) <= maxDim && (metadata.height ?? 0) <= maxDim) {
+    // Skipping the encode for already-small images left raw originals in
-      return { data: buf, mimeType: `image/${inputFormat}` };
+    // their native (often lossless PNG or full-quality) form, which could
-    }
+    // still bloat data URLs and trip the vision model's size limit.
-
-    // Resize dimension only — convert to PNG lossless to preserve detail
     const resized = await sharp(buf)
-      .resize(maxDim, maxDim, {
+      .resize(maxDim, maxDim, { fit: "inside", withoutEnlargement: true })
-        fit: "inside",
+      .jpeg({ quality: 85 })
-        withoutEnlargement: true,
-      })
-      .png()
       .toBuffer();
 
+    const inputFormat = metadata.format ?? "jpeg";
     log.debug(
       {
         originalSize: buf.length,
         originalFormat: inputFormat,
         resizedSize: resized.length,
-        reductionPct: Math.round(
+        reductionPct: Math.round(((buf.length - resized.length) / buf.length) * 100),
-          ((buf.length - resized.length) / buf.length) * 100,
-        ),
       },
-      "Image resized for vision analysis (lossless PNG)",
+      "Image resized for vision analysis (JPEG)",
     );
 
-    return { data: resized, mimeType: "image/png" };
+    return { data: resized, mimeType: "image/jpeg" };
   } catch (error) {
     log.warn(
       { error: error instanceof Error ? error.message : String(error) },

services/discord-gateway/tests/imageResizer.test.ts

@@ -0,0 +1,50 @@
+import { describe, expect, it } from "vitest";
+import sharp from "sharp";
+import { resizeImageForVision } from "../src/modules/attachment-upload/imageResizer.js";
+
+// Build a worst-case (poorly-compressing) 1024x1024 image, like a real photo.
+async function makeNoisyBuffer(): Promise<Buffer> {
+  const w = 1024,
+    h = 1024;
+  const buf = Buffer.alloc(w * h * 3);
+  let seed = 99;
+  const rnd = () => {
+    seed = (seed * 1103515245 + 12345) & 0x7fffffff;
+    return seed / 0x7fffffff;
+  };
+  for (let i = 0; i < buf.length; i++) buf[i] = Math.floor(rnd() * 256);
+  return sharp(buf, { raw: { width: w, height: h, channels: 3 } })
+    .png({ compressionLevel: 1 })
+    .toBuffer();
+}
+
+describe("resizeImageForVision — vision input encoding", () => {
+  it("always encodes to JPEG (not lossless PNG)", async () => {
+    const src = await makeNoisyBuffer();
+    // Source PNG is large & lossless (the old failure mode)
+    expect(src.length).toBeGreaterThan(300_000);
+
+    const { data, mimeType } = await resizeImageForVision(src, 1024);
+    expect(mimeType).toBe("image/jpeg");
+    // JPEG encoding must shrink the data URL payload well below MB range.
+    expect(data.length).toBeLessThan(800_000);
+  });
+
+  it("re-encodes already-small images (no passthrough of raw originals)", async () => {
+    const small = await sharp({
+      create: {
+        width: 200,
+        height: 200,
+        channels: 3,
+        background: { r: 200, g: 100, b: 50 },
+      },
+    })
+      .png()
+      .toBuffer();
+
+    const { data, mimeType } = await resizeImageForVision(small, 1024);
+    expect(mimeType).toBe("image/jpeg");
+    // Even a tiny PNG must come out re-encoded (bounded), not the raw PNG bytes.
+    expect(data.length).toBeLessThan(small.length);
+  });
+});