diff --git a/src/app/components/system-config/SecurityTab.tsx b/src/app/components/system-config/SecurityTab.tsx
index 73a513b..4994d8e 100644
--- a/src/app/components/system-config/SecurityTab.tsx
+++ b/src/app/components/system-config/SecurityTab.tsx
@@ -8,11 +8,13 @@ function TriState({
   value,
   onChange,
   confirmOff,
+  confirmOn,
 }: {
   label: string;
   value: boolean | null;
   onChange: (value: boolean | null) => void;
   confirmOff?: string;
+  confirmOn?: string;
 }) {
   return (
     <div className="flex items-center justify-between gap-3">
@@ -24,6 +26,7 @@ function TriState({
           const next =
             event.target.value === "default" ? null : event.target.value === "on";
           if (next === false && confirmOff && !window.confirm(confirmOff)) return;
+          if (next === true && confirmOn && !window.confirm(confirmOn)) return;
           onChange(next);
         }}
       >
@@ -87,6 +90,7 @@ export function SecurityTab({ draft, setDraft }: TabProps) {
         label="WebUI authentication"
         value={draft.security.authEnabled}
         confirmOff="Disabling authentication opens the UI to anyone who can reach it. Continue?"
+        confirmOn="Enabling authentication requires WEBUI_AUTH_SECRET to be set in the server environment. Without it, every page (including this dialog) will return 503 and recovery requires hand-editing ~/.evoscientist/system-config.json. Continue?"
         onChange={(authEnabled) => set({ authEnabled })}
       />
       <NullableNumber
diff --git a/src/lib/server/backupScheduler.test.ts b/src/lib/server/backupScheduler.test.ts
index 43a1bb5..e9f9c9f 100644
--- a/src/lib/server/backupScheduler.test.ts
+++ b/src/lib/server/backupScheduler.test.ts
@@ -57,4 +57,24 @@ describe("backupScheduler.tickBackupSchedule", () => {
     await scheduler.tickBackupSchedule(now + 10 * HOUR);
     expect(listBackups()).toHaveLength(0);
   });
+
+  it("records a failed attempt so the next tick does not retry", async () => {
+    const backendDir = fs.mkdtempSync(path.join(os.tmpdir(), "evosci-backend-"));
+    const config = getSystemConfig();
+    config.backup.backendDataDir = backendDir;
+    saveSystemConfig(config);
+    resetSystemConfigCacheForTests();
+    fs.rmSync(backendDir, { recursive: true, force: true }); // createBackup now fails
+
+    const { listErrorLogs, clearErrorLogs } = await import("./errorLogStore");
+    clearErrorLogs("system");
+
+    await scheduler.tickBackupSchedule(now);
+    expect(listBackups()).toHaveLength(0);
+    expect(listErrorLogs("system")).toHaveLength(1);
+
+    await scheduler.tickBackupSchedule(now + 60_000); // 1 min later: no retry
+    expect(listBackups()).toHaveLength(0);
+    expect(listErrorLogs("system")).toHaveLength(1);
+  });
 });
diff --git a/src/lib/server/backupScheduler.ts b/src/lib/server/backupScheduler.ts
index 50d9e7f..b29eb76 100644
--- a/src/lib/server/backupScheduler.ts
+++ b/src/lib/server/backupScheduler.ts
@@ -19,10 +19,12 @@ export async function tickBackupSchedule(now = Date.now()): Promise<void> {
   if (!schedule.enabled) return;
   const lastRunAt = globalState.__evoscientistBackupLastRunAt ?? 0;
   if (now - lastRunAt < schedule.intervalHours * 3_600_000) return;
+  // Record the attempt up front so a persistent failure retries on the next
+  // configured interval instead of on every tick, flooding the error log.
+  globalState.__evoscientistBackupLastRunAt = now;
   try {
     await createBackup("auto");
     pruneBackups(schedule.keepCount);
-    globalState.__evoscientistBackupLastRunAt = now;
   } catch (error) {
     try {
       appendErrorLog("system", {
diff --git a/src/lib/server/systemConfig.test.ts b/src/lib/server/systemConfig.test.ts
index 3704658..dc29c4f 100644
--- a/src/lib/server/systemConfig.test.ts
+++ b/src/lib/server/systemConfig.test.ts
@@ -95,6 +95,23 @@ describe("systemConfig", () => {
     ).toThrow(/backend data dir/i);
   });
 
+  it("rejects branding file names outside the fixed allowlist", () => {
+    expect(() =>
+      validateSystemConfig({ branding: { logoFile: "../../../tmp/x.svg" } })
+    ).toThrow(/logoFile/);
+    expect(() =>
+      validateSystemConfig({ branding: { logoFile: "favicon.png" } })
+    ).toThrow(/logoFile/);
+    expect(() =>
+      validateSystemConfig({ branding: { faviconFile: "../favicon.ico" } })
+    ).toThrow(/faviconFile/);
+    const valid = validateSystemConfig({
+      branding: { logoFile: "logo.svg", faviconFile: "favicon.ico" },
+    });
+    expect(valid.branding.logoFile).toBe("logo.svg");
+    expect(valid.branding.faviconFile).toBe("favicon.ico");
+  });
+
   it("derives effective security with env/code defaults", () => {
     const sec = effectiveSecurity();
     expect(sec.authEnabled).toBe(false); // WEBUI_AUTH_ENABLED unset
diff --git a/src/lib/server/systemConfig.ts b/src/lib/server/systemConfig.ts
index 8948477..265799a 100644
--- a/src/lib/server/systemConfig.ts
+++ b/src/lib/server/systemConfig.ts
@@ -131,6 +131,13 @@ function optInt(
   return value as number;
 }
 
+// Branding file fields feed an unauthenticated asset route, so only the
+// exact fixed names the upload route produces are acceptable.
+const BRANDING_FILE_RE: Record<"logoFile" | "faviconFile", RegExp> = {
+  logoFile: /^logo\.(png|jpe?g|svg)$/,
+  faviconFile: /^favicon\.(png|jpe?g|svg|ico)$/,
+};
+
 export function validateSystemConfig(input: unknown): SystemConfig {
   const source = isRecord(input) ? input : {};
   const merged = merge(source);
@@ -149,6 +156,13 @@ export function validateSystemConfig(input: unknown): SystemConfig {
     if (value !== null && typeof value !== "string") {
       throw new SystemConfigError(`branding.${key} must be a string or null.`);
     }
+    if (typeof value === "string" && !BRANDING_FILE_RE[key].test(value)) {
+      throw new SystemConfigError(
+        `branding.${key} must be a fixed asset file name (e.g. ${
+          key === "logoFile" ? "logo.svg" : "favicon.ico"
+        }).`
+      );
+    }
   }
 
   merged.loginTerms.enabled = merged.loginTerms.enabled === true;