diff --git a/src/queue/job-dispatch.ts b/src/queue/job-dispatch.ts
index eaffbfaf3..96435c281 100644
--- a/src/queue/job-dispatch.ts
+++ b/src/queue/job-dispatch.ts
@@ -107,7 +107,7 @@ export async function processJob(env: Env, message: JobMessage): Promise<void> {
         if (repositories.length > 0) {
           const delayStepSeconds =
             message.mode === "full" || message.mode === "resume" ? 45 : 15;
-          await Promise.all(
+          const settled = await Promise.allSettled(
             repositories.map((repo, index) => {
               const repoMessage: JobMessage = {
                 type: "backfill-registered-repos",
@@ -124,6 +124,23 @@ export async function processJob(env: Env, message: JobMessage): Promise<void> {
                 : env.JOBS.send(repoMessage);
             }),
           );
+          // #8355: Promise.allSettled (not Promise.all) so one repo's send failure never blocks or duplicates
+          // a sibling repo's send -- a bare Promise.all rejecting mid-fan-out previously caused the queue's own
+          // retry to re-run this ENTIRE repositories.map from scratch, duplicate-dispatching every repo whose
+          // send had already succeeded before the failure. Every repo's send is attempted exactly once
+          // regardless of an earlier one's outcome; a genuine failure still surfaces below (after every send
+          // has been attempted) so the cron invocation itself is marked failed for observability.
+          const failedRepoFullNames: string[] = [];
+          settled.forEach((result, index) => {
+            if (result.status === "rejected") {
+              const repoFullName = repositories[index]!.fullName;
+              failedRepoFullNames.push(repoFullName);
+              console.error(JSON.stringify({ level: "error", event: "backfill_registered_repos_fanout_send_failed", repoFullName, reason: String(result.reason) }));
+            }
+          });
+          if (failedRepoFullNames.length > 0) {
+            throw new Error(`backfill-registered-repos fan-out: ${failedRepoFullNames.length}/${repositories.length} repo send(s) failed: ${failedRepoFullNames.join(", ")}`);
+          }
           return;
         }
       }
diff --git a/test/unit/job-dispatch.test.ts b/test/unit/job-dispatch.test.ts
index fa3fafc0b..27b6962c1 100644
--- a/test/unit/job-dispatch.test.ts
+++ b/test/unit/job-dispatch.test.ts
@@ -2,6 +2,7 @@ import { afterEach, describe, expect, it, vi } from "vitest";
 
 import { processJob } from "../../src/queue/job-dispatch";
 import { createTestEnv } from "../helpers/d1";
+import { upsertInstallation, upsertRepositoryFromGitHub } from "../../src/db/repositories";
 import type { JobMessage } from "../../src/types";
 
 describe("processJob unknown job type (#5836)", () => {
@@ -39,3 +40,67 @@ describe("processJob unknown job type (#5836)", () => {
     expect(warnLogs.some((line) => line.includes("unknown_job_type_ignored"))).toBe(false);
   });
 });
+
+describe("processJob backfill-registered-repos fan-out isolation (#8355)", () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it("attempts every OTHER repo's send even when one repo's send rejects, and throws after the settle", async () => {
+    const sentTo: string[] = [];
+    const env = createTestEnv({
+      JOBS: {
+        async send(message: unknown) {
+          const repoFullName = (message as { repoFullName?: string }).repoFullName;
+          if (repoFullName) sentTo.push(repoFullName);
+          if (repoFullName === "owner/fails") throw new Error("simulated transient queue-send failure");
+          return undefined;
+        },
+      } as unknown as Queue,
+    });
+    await upsertInstallation(env, { action: "created", installation: { id: 9001, account: { login: "owner", id: 1, type: "Organization" }, target_type: "Organization", repository_selection: "selected", permissions: {}, events: [] } });
+    await upsertRepositoryFromGitHub(env, { name: "ok-1", full_name: "owner/ok-1", private: false, owner: { login: "owner" } }, 9001);
+    await upsertRepositoryFromGitHub(env, { name: "fails", full_name: "owner/fails", private: false, owner: { login: "owner" } }, 9001);
+    await upsertRepositoryFromGitHub(env, { name: "ok-2", full_name: "owner/ok-2", private: false, owner: { login: "owner" } }, 9001);
+
+    const errorLogs: string[] = [];
+    vi.spyOn(console, "error").mockImplementation((...args: unknown[]) => {
+      errorLogs.push(String(args[0]));
+    });
+
+    await expect(processJob(env, { type: "backfill-registered-repos", requestedBy: "schedule" } as JobMessage)).rejects.toThrow(
+      /backfill-registered-repos fan-out: 1\/3 repo send\(s\) failed: owner\/fails/,
+    );
+
+    // Every repo was attempted exactly once, regardless of the middle one's rejection.
+    expect(sentTo.sort()).toEqual(["owner/fails", "owner/ok-1", "owner/ok-2"]);
+
+    const failureLog = errorLogs.map((line) => JSON.parse(line) as Record<string, unknown>).find((log) => log.event === "backfill_registered_repos_fanout_send_failed");
+    expect(failureLog).toMatchObject({ level: "error", event: "backfill_registered_repos_fanout_send_failed", repoFullName: "owner/fails" });
+  });
+
+  it("does not throw or log a failure when every repo's send succeeds", async () => {
+    const sentTo: string[] = [];
+    const env = createTestEnv({
+      JOBS: {
+        async send(message: unknown) {
+          const repoFullName = (message as { repoFullName?: string }).repoFullName;
+          if (repoFullName) sentTo.push(repoFullName);
+          return undefined;
+        },
+      } as unknown as Queue,
+    });
+    await upsertInstallation(env, { action: "created", installation: { id: 9002, account: { login: "owner2", id: 2, type: "Organization" }, target_type: "Organization", repository_selection: "selected", permissions: {}, events: [] } });
+    await upsertRepositoryFromGitHub(env, { name: "ok-1", full_name: "owner2/ok-1", private: false, owner: { login: "owner2" } }, 9002);
+    await upsertRepositoryFromGitHub(env, { name: "ok-2", full_name: "owner2/ok-2", private: false, owner: { login: "owner2" } }, 9002);
+
+    const errorLogs: string[] = [];
+    vi.spyOn(console, "error").mockImplementation((...args: unknown[]) => {
+      errorLogs.push(String(args[0]));
+    });
+
+    await expect(processJob(env, { type: "backfill-registered-repos", requestedBy: "schedule" } as JobMessage)).resolves.toBeUndefined();
+    expect(sentTo.sort()).toEqual(["owner2/ok-1", "owner2/ok-2"]);
+    expect(errorLogs.some((line) => line.includes("backfill_registered_repos_fanout_send_failed"))).toBe(false);
+  });
+});