diff --git a/changelog.d/fixes/12969-batches-delete-completed-ownership.md b/changelog.d/fixes/12969-batches-delete-completed-ownership.md
index 77f6015eba..29824bf729 100644
--- a/changelog.d/fixes/12969-batches-delete-completed-ownership.md
+++ b/changelog.d/fixes/12969-batches-delete-completed-ownership.md
@@ -1 +1 @@
-- **fix(api):** `DELETE /v1/batches/delete-completed` now sweeps only the calling API key's own completed batches (batches with no owner stay out of a key-scoped sweep on purpose), with an explicit instance-wide mode reserved for authenticated dashboard sessions, audit logging of every sweep, a sanitized 500 on failure and an atomic sweep so a mid-way error never leaves a batch pointing at a nulled file (GHSA-wvxc-jp3v-5mg5)
+- **fix(api):** `DELETE /v1/batches/delete-completed` now sweeps only the calling API key's own completed batches (batches with no owner stay out of a key-scoped sweep on purpose), with an explicit instance-wide mode reserved for authenticated dashboard sessions, audit logging of every sweep, a sanitized 500 on failure and an atomic sweep so a mid-way error never leaves a batch pointing at a nulled file (GHSA-wvxc-jp3v-5mg5) ([#12969](https://github.com/diegosouzapw/OmniRoute/pull/12969))
diff --git a/src/app/api/v1/batches/delete-completed/route.ts b/src/app/api/v1/batches/delete-completed/route.ts
index fc9fac6de0..8340687235 100644
--- a/src/app/api/v1/batches/delete-completed/route.ts
+++ b/src/app/api/v1/batches/delete-completed/route.ts
@@ -15,24 +15,28 @@ export async function DELETE(request: Request) {
   const scope = await getApiKeyRequestScope(request);
   if (scope.rejection) return scope.rejection;
 
-  // Only an authenticated dashboard session sweeps the whole instance. Every
-  // other caller is an inference key and only sweeps its own completed batches,
-  // like the list/count siblings do — otherwise an ordinary key would delete
-  // every tenant's completed batches and null out their file contents
+  // A presented API key always scopes the sweep to that key — even when the
+  // request also carries a dashboard session cookie — exactly like the
+  // list/count siblings (`apiKeyId || undefined`), so a leaked or over-shared
+  // key can never widen a destructive sweep. Only a dashboard session WITHOUT a
+  // key sweeps the whole instance; otherwise an ordinary key would delete every
+  // tenant's completed batches and null out their file contents
   // (GHSA-wvxc-jp3v-5mg5). A caller that is neither gets 401; there is no
   // fallback that silently widens the sweep.
   let sweepScope: DeleteCompletedBatchesScope;
-  if (scope.isSessionAuth) {
-    sweepScope = { allTenants: true };
-  } else if (scope.apiKeyId) {
+  let mode: "instance" | "api_key";
+  if (scope.apiKeyId) {
     sweepScope = { apiKeyId: scope.apiKeyId };
+    mode = "api_key";
+  } else if (scope.isSessionAuth) {
+    sweepScope = { allTenants: true };
+    mode = "instance";
   } else {
     return NextResponse.json(
       { error: { message: "Authentication required", type: "invalid_request_error" } },
       { status: 401, headers: CORS_HEADERS }
     );
   }
-  const mode: "instance" | "api_key" = scope.isSessionAuth ? "instance" : "api_key";
 
   let result: ReturnType<typeof deleteCompletedBatches>;
   try {
@@ -42,7 +46,7 @@ export async function DELETE(request: Request) {
       route: LOG_ROUTE,
       mode,
       apiKeyId: scope.apiKeyId,
-      error: err instanceof Error ? err.message : String(err),
+      error: err instanceof Error ? { message: err.message, stack: err.stack } : String(err),
     });
     return NextResponse.json(buildErrorBody(500, "Failed to delete completed batches"), {
       status: 500,
@@ -57,11 +61,13 @@ export async function DELETE(request: Request) {
     deletedBatches: result.deletedBatches,
     deletedFiles: result.deletedFiles,
   };
-  if (mode === "instance") {
-    log.warn("BATCHES", "instance-wide completed-batch sweep", audit);
-  } else {
-    log.info("BATCHES", "completed-batch sweep", audit);
-  }
+  // A bulk delete is an audit event, not routine chatter: both modes log at
+  // warn so the trail survives APP_LOG_LEVEL=warn.
+  log.warn(
+    "BATCHES",
+    mode === "instance" ? "instance-wide completed-batch sweep" : "completed-batch sweep",
+    audit
+  );
 
   return NextResponse.json(
     { deleted: true, deletedBatches: result.deletedBatches, deletedFiles: result.deletedFiles },
diff --git a/src/lib/db/batches.ts b/src/lib/db/batches.ts
index 3f0aedbe64..b0e3225a10 100644
--- a/src/lib/db/batches.ts
+++ b/src/lib/db/batches.ts
@@ -452,6 +452,9 @@ export function deleteCompletedBatches(scope: DeleteCompletedBatchesScope): {
   if (!allTenants && !apiKeyId) {
     throw new Error("deleteCompletedBatches: apiKeyId required unless allTenants");
   }
+  if (allTenants && apiKeyId) {
+    throw new Error("deleteCompletedBatches: apiKeyId and allTenants are mutually exclusive");
+  }
 
   const db = getDbInstance();
 
diff --git a/tests/unit/batches-delete-completed-ownership-wvxc.test.ts b/tests/unit/batches-delete-completed-ownership-wvxc.test.ts
index 7fdfa7a857..3a5e4d46a6 100644
--- a/tests/unit/batches-delete-completed-ownership-wvxc.test.ts
+++ b/tests/unit/batches-delete-completed-ownership-wvxc.test.ts
@@ -139,6 +139,15 @@ describe("deleteCompletedBatches — ownership boundary (GHSA-wvxc-jp3v-5mg5)",
         }),
       /apiKeyId required unless allTenants/
     );
+    assert.throws(
+      // A mixed scope must be rejected, never silently widened to the instance.
+      () =>
+        (deleteCompletedBatches as unknown as (s: unknown) => unknown)({
+          apiKeyId: "key_survivor_wvxc",
+          allTenants: true,
+        }),
+      /mutually exclusive/
+    );
 
     assert.ok(getBatch(survivor.batch.id), "a rejected call must not delete anything");
     assert.strictEqual(
diff --git a/tests/unit/batches-delete-completed-route-scope.test.ts b/tests/unit/batches-delete-completed-route-scope.test.ts
index 6f7d4620c1..c4345fad88 100644
--- a/tests/unit/batches-delete-completed-route-scope.test.ts
+++ b/tests/unit/batches-delete-completed-route-scope.test.ts
@@ -112,16 +112,12 @@ describe("DELETE /api/v1/batches/delete-completed — caller scope (GHSA-wvxc-jp
     assert.ok(getBatch(victim.batch.id), "key B's batch still survives");
   });
 
-  it("a dashboard session sweeps the whole instance — even when the request also carries an API key", async () => {
-    const keyA = await createApiKey("wvxc-route-session-a", "machine-wvxc-sa", []);
+  it("a dashboard session WITHOUT a key sweeps the whole instance", async () => {
     const keyB = await createApiKey("wvxc-route-session-b", "machine-wvxc-sb", []);
     const other = seedCompletedBatch(keyB.id, "wvxc-route-session-other");
     const unowned = seedCompletedBatch(null, "wvxc-route-session-unowned");
 
-    const { res, body } = await callDelete({
-      Authorization: `Bearer ${keyA.key}`,
-      cookie: await sessionCookie(),
-    });
+    const { res, body } = await callDelete({ cookie: await sessionCookie() });
 
     assert.strictEqual(res.status, 200);
     assert.ok(
@@ -133,6 +129,33 @@ describe("DELETE /api/v1/batches/delete-completed — caller scope (GHSA-wvxc-jp
     assert.strictEqual(getFile(other.file.id), null, "session sweep soft-deletes the files too");
   });
 
+  it("a request carrying BOTH a session cookie and an API key is scoped to the key (the key wins, like GET /v1/batches)", async () => {
+    const keyA = await createApiKey("wvxc-route-both-a", "machine-wvxc-ba", []);
+    const keyB = await createApiKey("wvxc-route-both-b", "machine-wvxc-bb", []);
+    const own = seedCompletedBatch(keyA.id, "wvxc-route-both-own");
+    const other = seedCompletedBatch(keyB.id, "wvxc-route-both-other");
+    const unowned = seedCompletedBatch(null, "wvxc-route-both-unowned");
+
+    const { res, body } = await callDelete({
+      Authorization: `Bearer ${keyA.key}`,
+      cookie: await sessionCookie(),
+    });
+
+    assert.strictEqual(res.status, 200);
+    assert.strictEqual(body.deletedBatches, 1, "only key A's own completed batch is swept");
+    assert.strictEqual(getBatch(own.batch.id), null, "key A's own batch is swept");
+    assert.ok(
+      getBatch(other.batch.id),
+      "key B's batch survives — a presented key never widens the sweep"
+    );
+    assert.ok(getBatch(unowned.batch.id), "the unowned batch survives a key-scoped sweep");
+    assert.strictEqual(
+      getFileContent(other.file.id)?.toString(),
+      "wvxc-route-both-other",
+      "key B's file content is intact"
+    );
+  });
+
   it("rejects an unauthenticated request with 401 and deletes nothing", async () => {
     const keyB = await createApiKey("wvxc-route-401-b", "machine-wvxc-401", []);
     const seeded = seedCompletedBatch(keyB.id, "wvxc-route-401");