diff --git a/src/github/backfill.ts b/src/github/backfill.ts
index aaa3333993..600dd99c85 100644
--- a/src/github/backfill.ts
+++ b/src/github/backfill.ts
@@ -320,6 +320,25 @@ const DEFAULT_LIMITS: BackfillLimits = {
 
 const FRESH_SYNC_MS = 6 * 60 * 60 * 1000;
 const ERROR_BACKOFF_MS = 60 * 60 * 1000;
+
+/** Shared freshness/error-backoff decision (#4497): a repo whose last sync is either a fresh success (within
+ *  FRESH_SYNC_MS) or a recent error (within ERROR_BACKOFF_MS) should be skipped rather than re-synced, unless
+ *  the caller explicitly forces a refresh. Returns null when a sync should proceed (never synced, no completed
+ *  timestamp, or the existing sync is stale enough to redo). Shared by backfillRegisteredRepositories (the
+ *  admin-endpoint/test path) and enqueueRepositoryOpenDataBackfill (the real scheduled-cron path) so both
+ *  respect the SAME cadence -- previously only the former checked this, so the scheduled path re-synced every
+ *  registered repo every 30 minutes forever regardless of freshness or a permanent error state. */
+function syncFreshnessSkipReason(
+  syncState: RepoSyncStateRecord | null,
+  force: boolean | undefined,
+): { freshSuccess: boolean; recentError: boolean } | null {
+  if (force || !syncState?.lastCompletedAt || syncState.status === "never_synced") return null;
+  const ageMs = Date.now() - Date.parse(syncState.lastCompletedAt);
+  const freshSuccess =
+    (syncState.status === "success" || syncState.status === "partial" || syncState.status === "capped") && Number.isFinite(ageMs) && ageMs < FRESH_SYNC_MS;
+  const recentError = syncState.status === "error" && Number.isFinite(ageMs) && ageMs < ERROR_BACKOFF_MS;
+  return freshSuccess || recentError ? { freshSuccess, recentError } : null;
+}
 const SEGMENT_PAGE_BUDGET: Record<BackfillMode, number> = { light: 2, full: 10, resume: 10 };
 const PR_DETAIL_BATCH_SIZE: Record<BackfillMode, number> = { light: 12, full: 40, resume: 40 };
 // Caps how many NOT-yet-hydrated merged PRs get a `/pulls/{n}/files` fetch per `recent_merged_pull_requests`
@@ -422,26 +441,21 @@ export async function backfillRegisteredRepositories(
       };
     }
     const syncState = await getRepoSyncState(env, repo.fullName);
-    if (!options.force && syncState?.lastCompletedAt && syncState.status !== "never_synced") {
-      const ageMs = Date.now() - Date.parse(syncState.lastCompletedAt);
-      const freshSuccess =
-        (syncState.status === "success" || syncState.status === "partial" || syncState.status === "capped") && Number.isFinite(ageMs) && ageMs < FRESH_SYNC_MS;
-      const recentError = syncState.status === "error" && Number.isFinite(ageMs) && ageMs < ERROR_BACKOFF_MS;
-      if (freshSuccess || recentError) {
-        return {
-          repoFullName: repo.fullName,
-          status: "skipped",
-          openIssues: syncState.openIssuesCount,
-          openPullRequests: syncState.openPullRequestsCount,
-          recentMergedPullRequests: syncState.recentMergedPullRequestsCount,
-          warnings: [
-            freshSuccess
-              ? `Recent GitHub sync completed at ${syncState.lastCompletedAt}; use force=true for a manual refresh.`
-              : `Recent GitHub sync error recorded at ${syncState.lastCompletedAt}; backing off unless force=true.`,
-          ],
-          ...(recentError && syncState.errorSummary ? { errorSummary: syncState.errorSummary } : {}),
-        };
-      }
+    const skipReason = syncFreshnessSkipReason(syncState, options.force);
+    if (skipReason && syncState) {
+      return {
+        repoFullName: repo.fullName,
+        status: "skipped",
+        openIssues: syncState.openIssuesCount,
+        openPullRequests: syncState.openPullRequestsCount,
+        recentMergedPullRequests: syncState.recentMergedPullRequestsCount,
+        warnings: [
+          skipReason.freshSuccess
+            ? `Recent GitHub sync completed at ${syncState.lastCompletedAt}; use force=true for a manual refresh.`
+            : `Recent GitHub sync error recorded at ${syncState.lastCompletedAt}; backing off unless force=true.`,
+        ],
+        ...(skipReason.recentError && syncState.errorSummary ? { errorSummary: syncState.errorSummary } : {}),
+      };
     }
     return backfillRepository(env, repo, limits, mode);
   });
@@ -457,11 +471,28 @@ export async function enqueueRepositoryOpenDataBackfill(
   const mode = options.mode ?? "light";
   const settings = await resolveRepositorySettings(env, repo.fullName);
   if (!settings.backfillEnabled) return { ok: true, repoFullName: repo.fullName, status: "skipped", warnings: ["Backfill is disabled for this repository."] };
+  // #4497: checked BEFORE any GitHub/DB work below, mirroring backfillRegisteredRepositories's own freshness
+  // gate -- this is the path the real scheduled cron actually dispatches through (see that function's own
+  // routing comment), which previously had NO freshness/error-backoff check at all and re-synced every
+  // registered repo every 30 minutes forever, backing off neither for a fresh success nor a permanent error.
+  const previous = await getRepoSyncState(env, repo.fullName);
+  const skipReason = syncFreshnessSkipReason(previous, options.force);
+  if (skipReason && previous) {
+    return {
+      ok: true,
+      repoFullName: repo.fullName,
+      status: "skipped",
+      warnings: [
+        skipReason.freshSuccess
+          ? `Recent GitHub sync completed at ${previous.lastCompletedAt}; use force=true for a manual refresh.`
+          : `Recent GitHub sync error recorded at ${previous.lastCompletedAt}; backing off unless force=true.`,
+      ],
+    };
+  }
   const token = await tokenForRepo(env, repo);
   const sourceKind: RepoSyncSegmentRecord["sourceKind"] = repo.installationId && token !== env.GITHUB_PUBLIC_TOKEN ? "installation" : "github";
   const totals = await repoGithubTotalsForBackfill(env, repo, token, sourceKind);
   const startedAt = nowIso();
-  const previous = await getRepoSyncState(env, repo.fullName);
   await upsertRepoSyncState(env, {
     repoFullName: repo.fullName,
     status: "running",
diff --git a/test/unit/backfill.test.ts b/test/unit/backfill.test.ts
index 27726a11c0..3d347bd0ab 100644
--- a/test/unit/backfill.test.ts
+++ b/test/unit/backfill.test.ts
@@ -2239,6 +2239,182 @@ describe("GitHub backfill", () => {
     );
   });
 
+  it("INVARIANT (#4497): skips the scheduled per-repo backfill when the prior sync is a fresh success, without touching GitHub or writing any sync-state/segment jobs", async () => {
+    const sent: import("../../src/types").JobMessage[] = [];
+    const env = createTestEnv({
+      GITHUB_PUBLIC_TOKEN: "public-token",
+      JOBS: {
+        async send(message: import("../../src/types").JobMessage) {
+          sent.push(message);
+        },
+      } as unknown as Queue,
+    });
+    await seedRegisteredRepo(env);
+    await upsertRepoSyncState(env, {
+      repoFullName: "JSONbored/gittensory",
+      status: "success",
+      sourceKind: "github",
+      openIssuesCount: 5,
+      openPullRequestsCount: 3,
+      recentMergedPullRequestsCount: 10,
+      lastCompletedAt: new Date().toISOString(),
+      warnings: [],
+    });
+    vi.stubGlobal("fetch", async () => new Response("must not be called", { status: 500 }));
+
+    const result = await enqueueRepositoryOpenDataBackfill(env, { repoFullName: "JSONbored/gittensory", requestedBy: "schedule", mode: "light" });
+
+    expect(result).toMatchObject({ status: "skipped", warnings: [expect.stringContaining("Recent GitHub sync completed")] });
+    expect(sent).toEqual([]);
+    // Status stays "success" (unchanged) -- the scheduled path must not stamp "running" over a fresh state.
+    expect(await listRepoSyncStates(env)).toMatchObject([{ status: "success" }]);
+  });
+
+  it("INVARIANT (#4497): a syncState row stamped never_synced (distinct from no row at all) still proceeds with a real sync on the scheduled path", async () => {
+    const sent: import("../../src/types").JobMessage[] = [];
+    const env = createTestEnv({
+      GITHUB_PUBLIC_TOKEN: "public-token",
+      JOBS: {
+        async send(message: import("../../src/types").JobMessage) {
+          sent.push(message);
+        },
+      } as unknown as Queue,
+    });
+    await seedRegisteredRepo(env);
+    // A row EXISTS (unlike the "no prior state at all" case above) but its status is the placeholder
+    // "never_synced" -- e.g. stamped by an unrelated write that only carries over display fields (see
+    // fetchAndCachePrStateFields-style callers) before any real sync ever completed. This must never be
+    // mistaken for "a completed sync just happened."
+    await upsertRepoSyncState(env, {
+      repoFullName: "JSONbored/gittensory",
+      status: "never_synced",
+      sourceKind: "github",
+      openIssuesCount: 0,
+      openPullRequestsCount: 0,
+      recentMergedPullRequestsCount: 0,
+      lastCompletedAt: new Date().toISOString(),
+      warnings: [],
+    });
+    vi.stubGlobal("fetch", async (input: RequestInfo | URL) => {
+      if (input.toString() === "https://api.github.com/graphql") return githubTotalsResponse({ openIssues: 1, openPullRequests: 1, mergedPullRequests: 1, closedPullRequests: 0, labels: 0 });
+      return Response.json([]);
+    });
+
+    const result = await enqueueRepositoryOpenDataBackfill(env, { repoFullName: "JSONbored/gittensory", requestedBy: "schedule", mode: "light" });
+
+    expect(result.status).toBe("queued");
+    expect(sent.filter((message) => message.type === "backfill-repo-segment").length).toBeGreaterThan(0);
+  });
+
+  it("INVARIANT (#4497): a syncState past BOTH the fresh-success and error-backoff windows proceeds with a real sync, not a skip", async () => {
+    const sent: import("../../src/types").JobMessage[] = [];
+    const env = createTestEnv({
+      GITHUB_PUBLIC_TOKEN: "public-token",
+      JOBS: {
+        async send(message: import("../../src/types").JobMessage) {
+          sent.push(message);
+        },
+      } as unknown as Queue,
+    });
+    await seedRegisteredRepo(env);
+    // 7 hours ago: past FRESH_SYNC_MS (6h) for a success AND past ERROR_BACKOFF_MS (1h) were this an error --
+    // stale enough that the backfill must proceed normally rather than skip.
+    await upsertRepoSyncState(env, {
+      repoFullName: "JSONbored/gittensory",
+      status: "success",
+      sourceKind: "github",
+      openIssuesCount: 2,
+      openPullRequestsCount: 1,
+      recentMergedPullRequestsCount: 3,
+      lastCompletedAt: new Date(Date.now() - 7 * 60 * 60 * 1000).toISOString(),
+      warnings: [],
+    });
+    vi.stubGlobal("fetch", async (input: RequestInfo | URL) => {
+      if (input.toString() === "https://api.github.com/graphql") return githubTotalsResponse({ openIssues: 2, openPullRequests: 1, mergedPullRequests: 3, closedPullRequests: 0, labels: 0 });
+      return Response.json([]);
+    });
+
+    const result = await enqueueRepositoryOpenDataBackfill(env, { repoFullName: "JSONbored/gittensory", requestedBy: "schedule", mode: "light" });
+
+    expect(result.status).toBe("queued");
+    expect(sent.filter((message) => message.type === "backfill-repo-segment").length).toBeGreaterThan(0);
+  });
+
+  it("INVARIANT (#4497): backs off the scheduled per-repo backfill when the prior sync errored recently, instead of retrying every tick", async () => {
+    const sent: import("../../src/types").JobMessage[] = [];
+    const env = createTestEnv({
+      GITHUB_PUBLIC_TOKEN: "public-token",
+      JOBS: {
+        async send(message: import("../../src/types").JobMessage) {
+          sent.push(message);
+        },
+      } as unknown as Queue,
+    });
+    await seedRegisteredRepo(env);
+    await upsertRepoSyncState(env, {
+      repoFullName: "JSONbored/gittensory",
+      status: "error",
+      sourceKind: "github",
+      openIssuesCount: 0,
+      openPullRequestsCount: 0,
+      recentMergedPullRequestsCount: 0,
+      lastCompletedAt: new Date().toISOString(),
+      errorSummary: "rate limited",
+      warnings: [],
+    });
+    vi.stubGlobal("fetch", async () => new Response("must not be called", { status: 500 }));
+
+    const result = await enqueueRepositoryOpenDataBackfill(env, { repoFullName: "JSONbored/gittensory", requestedBy: "schedule", mode: "light" });
+
+    expect(result).toMatchObject({ status: "skipped", warnings: [expect.stringContaining("backing off")] });
+    expect(sent).toEqual([]);
+  });
+
+  it("REGRESSION (#4497, endless-scheduled-resync incident): two scheduled dispatches within the freshness window only sync once -- previously every registered repo was re-synced every 30 min forever regardless of freshness or a permanent error state", async () => {
+    const sent: import("../../src/types").JobMessage[] = [];
+    const env = createTestEnv({
+      GITHUB_PUBLIC_TOKEN: "public-token",
+      JOBS: {
+        async send(message: import("../../src/types").JobMessage) {
+          sent.push(message);
+        },
+      } as unknown as Queue,
+    });
+    await seedRegisteredRepo(env);
+    vi.stubGlobal("fetch", async (input: RequestInfo | URL) => {
+      if (input.toString() === "https://api.github.com/graphql") return githubTotalsResponse({ openIssues: 4, openPullRequests: 2, mergedPullRequests: 9, closedPullRequests: 1, labels: 1 });
+      return Response.json([]);
+    });
+
+    // First scheduled tick: no prior sync state -> a real sync proceeds and stamps a fresh success.
+    const first = await enqueueRepositoryOpenDataBackfill(env, { repoFullName: "JSONbored/gittensory", requestedBy: "schedule", mode: "light" });
+    expect(first.status).toBe("queued");
+    const segmentJobsAfterFirst = sent.filter((message) => message.type === "backfill-repo-segment").length;
+    expect(segmentJobsAfterFirst).toBeGreaterThan(0);
+    await upsertRepoSyncState(env, {
+      repoFullName: "JSONbored/gittensory",
+      status: "success",
+      sourceKind: "github",
+      openIssuesCount: 4,
+      openPullRequestsCount: 2,
+      recentMergedPullRequestsCount: 9,
+      lastCompletedAt: new Date().toISOString(),
+      warnings: [],
+    });
+
+    // Second scheduled tick, simulating the next ~30-min cron cadence while still fresh: must be skipped, not
+    // re-synced -- this is the exact incident shape (the scheduled path previously had no freshness check at
+    // all, so this second tick would have unconditionally re-fetched totals and re-enqueued all 4 segments).
+    const second = await enqueueRepositoryOpenDataBackfill(env, { repoFullName: "JSONbored/gittensory", requestedBy: "schedule", mode: "light" });
+    expect(second.status).toBe("skipped");
+    expect(sent.filter((message) => message.type === "backfill-repo-segment").length).toBe(segmentJobsAfterFirst);
+
+    // An explicit force still bypasses the freshness gate -- the override path is preserved.
+    const forced = await enqueueRepositoryOpenDataBackfill(env, { repoFullName: "JSONbored/gittensory", requestedBy: "schedule", mode: "light", force: true });
+    expect(forced.status).toBe("queued");
+    expect(sent.filter((message) => message.type === "backfill-repo-segment").length).toBeGreaterThan(segmentJobsAfterFirst);
+  });
+
   it("reuses a fresh repo totals snapshot when queueing segmented backfills", async () => {
     vi.useFakeTimers();
     vi.setSystemTime(new Date("2026-05-25T00:05:00.000Z"));