diff --git a/src/lib/documents/__tests__/native-canvas-support.test.ts b/src/lib/documents/__tests__/native-canvas-support.test.ts
index df978c965..df282df1d 100644
--- a/src/lib/documents/__tests__/native-canvas-support.test.ts
+++ b/src/lib/documents/__tests__/native-canvas-support.test.ts
@@ -115,6 +115,6 @@ describe("generateThumbnail behind a closed gate", () => {
       Buffer.from([0xff, 0xd8, 0xff]),
       "image/jpeg",
     );
-    expect(result).toEqual({ ok: false });
+    expect(result).toEqual({ ok: false, reason: "native-canvas-unsupported" });
   });
 });
diff --git a/src/lib/documents/__tests__/thumbnail.test.ts b/src/lib/documents/__tests__/thumbnail.test.ts
index 59a03ab64..05a2630d6 100644
--- a/src/lib/documents/__tests__/thumbnail.test.ts
+++ b/src/lib/documents/__tests__/thumbnail.test.ts
@@ -126,19 +126,19 @@ describe("generateThumbnail", () => {
   it("returns { ok: false } for an unsupported MIME type", async () => {
     await expect(
       generateThumbnail(Buffer.from("plain text"), "text/plain"),
-    ).resolves.toEqual({ ok: false });
+    ).resolves.toEqual({ ok: false, reason: "unsupported-type" });
   });
 
   it("returns { ok: false } and never throws on malformed image bytes", async () => {
     await expect(
       generateThumbnail(Buffer.from("not a real image"), "image/png"),
-    ).resolves.toEqual({ ok: false });
+    ).resolves.toEqual({ ok: false, reason: "error" });
   });
 
   it("returns { ok: false } on a malformed PDF", async () => {
     await expect(
       generateThumbnail(Buffer.from("not a pdf"), "application/pdf"),
-    ).resolves.toEqual({ ok: false });
+    ).resolves.toEqual({ ok: false, reason: "raster-failed" });
   });
 
   it("refuses a decompression bomb before decoding (pixel cap)", async () => {
@@ -153,6 +153,7 @@ describe("generateThumbnail", () => {
     bomb.writeUInt32BE(30_000, 20); // height
     await expect(generateThumbnail(bomb, "image/png")).resolves.toEqual({
       ok: false,
+      reason: "pixel-cap",
     });
   });
 
@@ -164,6 +165,6 @@ describe("generateThumbnail", () => {
     loadImageMock.mockResolvedValueOnce({ width: 30_000, height: 30_000 });
     await expect(
       generateThumbnail(Buffer.from("desynced jpeg bytes"), "image/jpeg"),
-    ).resolves.toEqual({ ok: false });
+    ).resolves.toEqual({ ok: false, reason: "pixel-cap" });
   });
 });
diff --git a/src/lib/documents/thumbnail.ts b/src/lib/documents/thumbnail.ts
index 8d975954f..26ed69c1b 100644
--- a/src/lib/documents/thumbnail.ts
+++ b/src/lib/documents/thumbnail.ts
@@ -157,9 +157,23 @@ export interface Thumbnail {
   height: number;
 }
 
+/**
+ * Why no preview was made. `unsupported-type` is the expected answer for an
+ * Office file or a text document; every other reason means a preview should
+ * have existed, so the thumbnail job logs it as a warning.
+ */
+export type ThumbnailSkipReason =
+  | "unsupported-type"
+  | "native-canvas-unsupported"
+  | "pixel-cap"
+  | "raster-failed"
+  | "empty-render"
+  | "error";
+
 /** Best-effort generation outcome — never an exception. */
 export type ThumbnailResult =
-  { ok: true; thumbnail: Thumbnail } | { ok: false };
+  | { ok: true; thumbnail: Thumbnail }
+  | { ok: false; reason: ThumbnailSkipReason };
 
 // Minimal structural types for the slice of `@napi-rs/canvas` this module uses.
 // A type-only shape (erased at build) so we never eagerly evaluate the module
@@ -229,7 +243,7 @@ export async function generateThumbnail(
         action: { name: "documents.thumbnail.rejected" },
         meta: { reason: "native_canvas_unsupported" },
       });
-      return { ok: false };
+      return { ok: false, reason: "native-canvas-unsupported" };
     }
     // Lazy import: keeps @napi-rs/canvas (+ transitively pdfjs on the PDF path)
     // out of the eager server chunk. Resolved on first generation, then cached.
@@ -244,7 +258,7 @@ export async function generateThumbnail(
           action: { name: "documents.thumbnail.rejected" },
           meta: { source: "image", reason: "pixel_cap", pixels },
         });
-        return { ok: false };
+        return { ok: false, reason: "pixel-cap" };
       }
       const image = await napi.loadImage(bytes);
       // Post-decode backstop: the header sniff returns null on any marker
@@ -260,10 +274,10 @@ export async function generateThumbnail(
             pixels: image.width * image.height,
           },
         });
-        return { ok: false };
+        return { ok: false, reason: "pixel-cap" };
       }
       const thumb = drawScaledJpeg(napi, image);
-      if (!thumb) return { ok: false };
+      if (!thumb) return { ok: false, reason: "empty-render" };
       annotate({
         action: { name: "documents.thumbnail.ok" },
         meta: { source: "image", width: thumb.width, height: thumb.height },
@@ -274,11 +288,13 @@ export async function generateThumbnail(
     if (mimeType === "application/pdf") {
       // Page 1 only — a preview never renders the whole document.
       const raster = await rasterizePdf(bytes, 1);
-      if (!raster.ok || raster.images.length === 0) return { ok: false };
+      if (!raster.ok || raster.images.length === 0) {
+        return { ok: false, reason: "raster-failed" };
+      }
       const pageJpeg = Buffer.from(raster.images[0]!.dataBase64, "base64");
       const image = await napi.loadImage(pageJpeg);
       const thumb = drawScaledJpeg(napi, image);
-      if (!thumb) return { ok: false };
+      if (!thumb) return { ok: false, reason: "empty-render" };
       annotate({
         action: { name: "documents.thumbnail.ok" },
         meta: { source: "pdf", width: thumb.width, height: thumb.height },
@@ -287,7 +303,7 @@ export async function generateThumbnail(
     }
 
     // Every other MIME (Office/text/TIFF/HEIC/XML/JSON) — no preview.
-    return { ok: false };
+    return { ok: false, reason: "unsupported-type" };
   } catch (err) {
     annotate({
       action: { name: "documents.thumbnail.failed" },
@@ -297,6 +313,6 @@ export async function generateThumbnail(
         message: err instanceof Error ? err.message.slice(0, 300) : String(err),
       },
     });
-    return { ok: false };
+    return { ok: false, reason: "error" };
   }
 }
diff --git a/src/lib/jobs/__tests__/document-thumbnail.test.ts b/src/lib/jobs/__tests__/document-thumbnail.test.ts
new file mode 100644
index 000000000..4270507d1
--- /dev/null
+++ b/src/lib/jobs/__tests__/document-thumbnail.test.ts
@@ -0,0 +1,98 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+/**
+ * GitHub #1124 — the thumbnail job ran 355 times on one instance, left
+ * sixteen PDFs without a preview, and the log held not one line about it:
+ * the job opened no wide event, so every annotation went nowhere. Pins: each
+ * run is a `job.document_thumbnail` background event; a run that should have
+ * made a preview and did not is raised to `warn` with the reason; a type that
+ * never has a preview stays at info.
+ */
+
+const { evt, findFirst, upsert, generateThumbnail, withBackgroundEvent } =
+  vi.hoisted(() => {
+    const evt = { addMeta: vi.fn(), elevateLevel: vi.fn() };
+    return {
+      evt,
+      findFirst: vi.fn(),
+      upsert: vi.fn(),
+      generateThumbnail: vi.fn(),
+      withBackgroundEvent: vi.fn(
+        async (_name: string, fn: (e: typeof evt) => Promise<unknown>) =>
+          fn(evt),
+      ),
+    };
+  });
+
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    inboundDocument: { findFirst },
+    documentThumbnail: { upsert },
+  },
+}));
+vi.mock("@/lib/documents/store", () => ({
+  decryptDocumentContent: vi.fn(() => Buffer.from("%PDF-1.7")),
+  encryptThumbnail: vi.fn(() => new Uint8Array([1])),
+}));
+vi.mock("@/lib/documents/thumbnail", () => ({ generateThumbnail }));
+vi.mock("@/lib/jobs/boss-instance", () => ({ getGlobalBoss: vi.fn() }));
+vi.mock("@/lib/logging/context", () => ({ annotate: vi.fn() }));
+vi.mock("@/lib/logging/background", () => ({ withBackgroundEvent }));
+
+import { runDocumentThumbnail } from "../document-thumbnail";
+
+const DOC = {
+  id: "doc-1",
+  mimeType: "application/pdf",
+  contentEncrypted: new Uint8Array([1]),
+  contentCodec: "binary2",
+  thumbnail: null,
+};
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  findFirst.mockResolvedValue(DOC);
+});
+
+describe("runDocumentThumbnail wide event", () => {
+  it("runs inside a background event named for the job", async () => {
+    generateThumbnail.mockResolvedValue({ ok: false, reason: "raster-failed" });
+    await runDocumentThumbnail({ userId: "user-1", documentId: "doc-1" });
+    expect(withBackgroundEvent).toHaveBeenCalledWith(
+      "job.document_thumbnail",
+      expect.any(Function),
+    );
+    expect(evt.addMeta).toHaveBeenCalledWith("document_id", "doc-1");
+  });
+
+  it("warns with the reason when a PDF gets no preview", async () => {
+    generateThumbnail.mockResolvedValue({ ok: false, reason: "error" });
+    await runDocumentThumbnail({ userId: "user-1", documentId: "doc-1" });
+    expect(evt.elevateLevel).toHaveBeenCalledWith("warn");
+    expect(evt.addMeta).toHaveBeenCalledWith(
+      "thumbnail_missing_reason",
+      "error",
+    );
+    expect(upsert).not.toHaveBeenCalled();
+  });
+
+  it("stays at info for a type that never has a preview", async () => {
+    findFirst.mockResolvedValue({ ...DOC, mimeType: "text/plain" });
+    generateThumbnail.mockResolvedValue({
+      ok: false,
+      reason: "unsupported-type",
+    });
+    await runDocumentThumbnail({ userId: "user-1", documentId: "doc-1" });
+    expect(evt.elevateLevel).not.toHaveBeenCalled();
+  });
+
+  it("stores the preview and stays at info when one is made", async () => {
+    generateThumbnail.mockResolvedValue({
+      ok: true,
+      thumbnail: { jpeg: Buffer.from([0xff, 0xd8]), width: 2, height: 3 },
+    });
+    await runDocumentThumbnail({ userId: "user-1", documentId: "doc-1" });
+    expect(upsert).toHaveBeenCalledOnce();
+    expect(evt.elevateLevel).not.toHaveBeenCalled();
+  });
+});
diff --git a/src/lib/jobs/document-thumbnail.ts b/src/lib/jobs/document-thumbnail.ts
index 91a8d44ed..1b0a1a91d 100644
--- a/src/lib/jobs/document-thumbnail.ts
+++ b/src/lib/jobs/document-thumbnail.ts
@@ -15,6 +15,12 @@
  * kind icon), and `runDocumentThumbnail` returns cleanly so pg-boss does not
  * retry it. Only an unexpected throw (a DB hiccup) propagates for retry.
  *
+ * Each run is one background wide event (`job.document_thumbnail`). A run
+ * that should have produced a preview and did not is raised to `warn` with
+ * the reason, so a document left with its kind icon is explained in the log.
+ * Without the event every annotation below went nowhere: a whole class of
+ * PDFs went without previews for weeks and the log never said so.
+ *
  * The queue MUST be registered in the maintenance registrar
  * (`src/lib/jobs/reminder/register-maintenance.ts`) so pg-boss provisions it.
  */
@@ -25,6 +31,7 @@ import {
 } from "@/lib/documents/store";
 import { generateThumbnail } from "@/lib/documents/thumbnail";
 import { getGlobalBoss } from "@/lib/jobs/boss-instance";
+import { withBackgroundEvent } from "@/lib/logging/background";
 import { annotate } from "@/lib/logging/context";
 
 export const DOCUMENT_THUMBNAIL_QUEUE = "document-thumbnail";
@@ -49,7 +56,20 @@ export async function runDocumentThumbnail(
 ): Promise<void> {
   const { userId, documentId } = payload;
   if (!userId || !documentId) return;
+  await withBackgroundEvent("job.document_thumbnail", async (evt) => {
+    evt.addMeta("document_id", documentId);
+    await renderThumbnail(userId, documentId, (reason) => {
+      evt.addMeta("thumbnail_missing_reason", reason);
+      evt.elevateLevel("warn");
+    });
+  });
+}
 
+async function renderThumbnail(
+  userId: string,
+  documentId: string,
+  warn: (reason: string) => void,
+): Promise<void> {
   // Owner-scoped load; the blob column is selected ONLY here (the job that
   // renders the preview), never in the list/detail queries. Skip a document
   // that already has a thumbnail so a re-enqueue is a cheap no-op.
@@ -84,6 +104,7 @@ export async function runDocumentThumbnail(
       action: { name: "documents.thumbnail.decryptFailed" },
       meta: { documentId },
     });
+    warn("decrypt-failed");
     return;
   }
 
@@ -91,8 +112,11 @@ export async function runDocumentThumbnail(
   if (!result.ok) {
     annotate({
       action: { name: "documents.thumbnail.run" },
-      meta: { documentId, generated: false },
+      meta: { documentId, generated: false, mimeType: document.mimeType },
     });
+    // An Office or text document has no preview by design; anything else
+    // was meant to get one.
+    if (result.reason !== "unsupported-type") warn(result.reason);
     return;
   }