diff --git a/frontend/src/hooks/useWebcamFrames.ts b/frontend/src/hooks/useWebcamFrames.ts
index 71ed6097..6e6f6f70 100644
--- a/frontend/src/hooks/useWebcamFrames.ts
+++ b/frontend/src/hooks/useWebcamFrames.ts
@@ -44,7 +44,22 @@ export interface UseWebcamFramesResult {
 const FRAME_WIDTH = 320;
 const FRAME_HEIGHT = 240;
 const FRAME_INTERVAL_MS = 100; // 10 fps
-const JPEG_QUALITY = 0.6;
+// Keep JPEGs comfortably under the QEMU emulator's 8 KiB-per-frame
+// deliverable budget (8 EOFs × 1024 bytes from the cam_hal default
+// 16-descriptor ring). Quality 0.6 produces ~10-12 KiB which gets
+// truncated mid-stream in the firmware framebuffer — cam_verify_jpeg_eoi
+// accepts the frame because we inject FF D9 at byte 8190, but
+// jpg2rgb565() (the upstream decoder) rejects the truncated JPEG with
+// "JPG Decompression Failed! Data format error".
+//
+// Quality 0.25 produces ~3-5 KiB JPEGs that fit the budget entirely
+// AND decode cleanly because the natural EOI marker lands well before
+// our injection point. Visual quality is roughly equivalent to a
+// VGA-era webcam capture — totally serviceable for an emulator preview.
+//
+// See test/test-esp32-cam/autosearch/14_complete_emulation.md "Bug #9"
+// for the full forensic trace of the truncation issue.
+const JPEG_QUALITY = 0.25;
 
 export function useWebcamFrames(): UseWebcamFramesResult {
   const [status, setStatus] = useState<WebcamStatus>('idle');