diff --git a/src/github/backfill.ts b/src/github/backfill.ts
index b568e85385..34dd9d200d 100644
--- a/src/github/backfill.ts
+++ b/src/github/backfill.ts
@@ -2793,6 +2793,19 @@ async function reduceLiveCiAggregate(
   const { checkRuns, statuses, requiredContexts, checkRunsIncomplete, statusIncomplete, fetchSuites } = inputs;
   const enforceRequiredOnly = requiredContexts != null && requiredContexts.size > 0;
   const isRequired = (name: string): boolean => !enforceRequiredOnly || requiredContexts!.has(name);
+  // Deliberately the OPPOSITE unknown-case default from isRequired() above, and used ONLY for a third-party
+  // app's own action_required verdict (see isThirdPartyActionRequired below). isRequired()'s "assume required
+  // unless proven otherwise" is the right fail-safe for a genuine CI failure (an unconfirmed-required broken
+  // build should still block). But that same default silently reopened #4414 for any repo with NO
+  // branch-protection required-contexts configured at all (enforceRequiredOnly false, e.g. one that never set
+  // up required status checks): isRequired() returns true for every name in that mode, so a third-party
+  // advisory-only check-run (Superagent's "Contributor trust", never meant to gate anything on its own) got
+  // folded into failingDetails and auto-closed real contributor PRs again, on repos exactly like #4812's
+  // metagraphed (confirmed empty required_status_checks.contexts) -- despite #4414 believing it had already
+  // fixed this. A third-party app's action_required is a POLICY OPINION, not "your code is broken"; the
+  // failure mode of wrongly closing a real contributor's clean PR is worse than under-enforcing a check no
+  // maintainer ever formally required, so this one path needs POSITIVE evidence, not a fail-safe assumption.
+  const isConfirmedRequired = (name: string): boolean => enforceRequiredOnly && requiredContexts!.has(name);
   const failingDetails: LiveCiAggregate["failingDetails"] = [];
   const nonRequiredFailingDetails: LiveCiAggregate["nonRequiredFailingDetails"] = [];
   let total = 0;
@@ -2824,14 +2837,18 @@ async function reduceLiveCiAggregate(
     // the same way conflates them (#4414 regressed exactly this -- a non-required advisory check started
     // auto-closing real contributor PRs). This is NOT the github-actions "awaiting maintainer Approve and run"
     // case the action_required exclusion above exists for: non-Actions apps use their own conclusion as a policy
-    // signal. Conservative: an unknown/absent app slug is NOT treated as third-party here.
+    // signal. Conservative: an unknown/absent app slug is NOT treated as third-party here. Gated on
+    // isConfirmedRequired (not isRequired, see its own doc comment above): a repo with NO branch-protection
+    // required-contexts configured at all must NOT fall back to treating this as required just because we
+    // don't know better -- that fail-safe belongs to genuine CI failures, not a third-party opinion check.
     const isThirdPartyActionRequired = conclusion === "action_required" && status === "completed" && appSlug !== "" && appSlug !== "github-actions";
-    if (isThirdPartyActionRequired && isRequired(run.name)) {
+    if (isThirdPartyActionRequired && isConfirmedRequired(run.name)) {
       const summary = checkRunSummary(run);
       failingDetails.push({ name: run.name, ...(summary ? { summary } : {}), ...(run.details_url ? { detailsUrl: run.details_url } : {}) });
     } else if (isThirdPartyActionRequired) {
-      // Non-required: visible (never silently folded into "passed" either, unlike the pre-#4414 behavior) but
-      // non-blocking -- routed to nonRequiredFailingDetails, which never feeds ciState or a close decision.
+      // Non-required (or required-contexts unconfirmed, e.g. no branch protection configured): visible (never
+      // silently folded into "passed" either, unlike the pre-#4414 behavior) but non-blocking -- routed to
+      // nonRequiredFailingDetails, which never feeds ciState or a close decision.
       const summary = checkRunSummary(run);
       nonRequiredFailingDetails.push({ name: run.name, ...(summary ? { summary } : {}), ...(run.details_url ? { detailsUrl: run.details_url } : {}) });
     } else if (conclusion ? CI_FAILING_CONCLUSIONS.has(conclusion) : false) {
diff --git a/test/unit/backfill.test.ts b/test/unit/backfill.test.ts
index 1c3b12f2db..76c915f0de 100644
--- a/test/unit/backfill.test.ts
+++ b/test/unit/backfill.test.ts
@@ -4602,6 +4602,71 @@ describe("GitHub backfill", () => {
       ]);
     });
 
+    it("REGRESSION (#4812): a third-party action_required check-run on a repo with NO branch-protection required contexts configured at all is still non-blocking, not folded into failingDetails by the 'assume required when unknown' fallback", async () => {
+      // Reproduces PR #4812 (JSONbored/metagraphed) exactly: the repo's real branch protection returns
+      // required_status_checks.contexts: [] (confirmed via the live GitHub API) -- fetchRequiredStatusContexts
+      // maps that to an EMPTY Set, not null, so enforceRequiredOnly is false. Before this fix, isRequired()'s
+      // "!enforceRequiredOnly || ..." made every name "required" in that mode, silently reopening #4414 for
+      // any repo that simply never configured GitHub-native required status checks -- Contributor trust
+      // (Superagent's advisory, never-should-block signal) got folded into failingDetails and auto-closed a
+      // real contributor's PR with every actual CI check (tests, coverage, ui) green.
+      const env = createTestEnv({ GITHUB_PUBLIC_TOKEN: "public-token" });
+      vi.stubGlobal("fetch", async (input: RequestInfo | URL) => {
+        const url = input.toString();
+        if (url.includes("/check-runs?")) {
+          return Response.json({
+            check_runs: [
+              { name: "test", status: "completed", conclusion: "success", app: { slug: "github-actions" } },
+              { name: "ui", status: "completed", conclusion: "success", app: { slug: "github-actions" } },
+              {
+                name: "Contributor trust",
+                status: "completed",
+                conclusion: "action_required",
+                app: { slug: "superagent-security" },
+                output: { title: "Contributor flagged for review" },
+              },
+            ],
+          });
+        }
+        if (url.includes("/status?")) return Response.json({ statuses: [{ context: "codecov/patch", state: "success" }] });
+        if (url.includes("/check-suites?")) return Response.json({ check_suites: [{ status: "completed", app: { slug: "github-actions" } }] });
+        return new Response("not found", { status: 404 });
+      });
+
+      const aggregate = await fetchLiveCiAggregate(env, "JSONbored/metagraphed", "sha4812", "public-token", new Set());
+
+      expect(aggregate.ciState).toBe("passed");
+      expect(aggregate.failingDetails).toEqual([]);
+      expect(aggregate.nonRequiredFailingDetails).toEqual([{ name: "Contributor trust", summary: "Contributor flagged for review" }]);
+    });
+
+    it("REGRESSION (#4812): the same holds when required-status-context fetch outright failed (null), not just when it confirmed an empty list", async () => {
+      // A distinct origin from the empty-Set case above (a 403/fetch error rather than a confirmed-empty
+      // response), but must resolve the same way: no POSITIVE confirmation that Contributor trust is required
+      // means it stays advisory, never a close reason.
+      const env = createTestEnv({ GITHUB_PUBLIC_TOKEN: "public-token" });
+      vi.stubGlobal("fetch", async (input: RequestInfo | URL) => {
+        const url = input.toString();
+        if (url.includes("/check-runs?")) {
+          return Response.json({
+            check_runs: [
+              { name: "test", status: "completed", conclusion: "success", app: { slug: "github-actions" } },
+              { name: "Contributor trust", status: "completed", conclusion: "action_required", app: { slug: "superagent-security" } },
+            ],
+          });
+        }
+        if (url.includes("/status?")) return Response.json({ statuses: [] });
+        if (url.includes("/check-suites?")) return Response.json({ check_suites: [{ status: "completed", app: { slug: "github-actions" } }] });
+        return new Response("not found", { status: 404 });
+      });
+
+      const aggregate = await fetchLiveCiAggregate(env, "JSONbored/metagraphed", "sha4812b", "public-token", null);
+
+      expect(aggregate.ciState).toBe("passed");
+      expect(aggregate.failingDetails).toEqual([]);
+      expect(aggregate.nonRequiredFailingDetails).toEqual([{ name: "Contributor trust" }]);
+    });
+
     it("a non-required third-party action_required check-run with no output/details_url still lands in nonRequiredFailingDetails, bare (name-only)", async () => {
       const env = createTestEnv({ GITHUB_PUBLIC_TOKEN: "public-token" });
       vi.stubGlobal("fetch", async (input: RequestInfo | URL) => {