diff --git a/desktop/src/features/sidebar/ui/ChannelSectionDialogs.tsx b/desktop/src/features/sidebar/ui/ChannelSectionDialogs.tsx
index 6b054fa600..beaebfb1ee 100644
--- a/desktop/src/features/sidebar/ui/ChannelSectionDialogs.tsx
+++ b/desktop/src/features/sidebar/ui/ChannelSectionDialogs.tsx
@@ -282,6 +282,8 @@ export type LeaveChannelAlertDialogProps = {
   onOpenChange: (open: boolean) => void;
   channelName: string;
   onConfirm: () => void;
+  error?: Error | null;
+  isPending?: boolean;
 };
 
 export function LeaveChannelAlertDialog({
@@ -289,6 +291,8 @@ export function LeaveChannelAlertDialog({
   onOpenChange,
   channelName,
   onConfirm,
+  error,
+  isPending,
 }: LeaveChannelAlertDialogProps) {
   return (
     <AlertDialog open={open} onOpenChange={onOpenChange}>
@@ -299,13 +303,17 @@ export function LeaveChannelAlertDialog({
             {`Leave "${channelName}"? You'll stop receiving its messages and can rejoin later.`}
           </AlertDialogDescription>
         </AlertDialogHeader>
+        {error instanceof Error ? (
+          <p className="text-sm text-destructive">{error.message}</p>
+        ) : null}
         <AlertDialogFooter>
-          <AlertDialogCancel>Cancel</AlertDialogCancel>
+          <AlertDialogCancel disabled={isPending}>Cancel</AlertDialogCancel>
           <AlertDialogAction
             className="bg-destructive text-destructive-foreground hover:bg-destructive/90"
+            disabled={isPending}
             onClick={onConfirm}
           >
-            Leave
+            {isPending ? "Leaving..." : "Leave"}
           </AlertDialogAction>
         </AlertDialogFooter>
       </AlertDialogContent>
@@ -325,14 +333,17 @@ export function useLeaveChannelDialog() {
     <LeaveChannelAlertDialog
       open={target !== null}
       onOpenChange={(open) => {
-        if (!open) setTarget(null);
+        if (!open && !leaveChannel.isPending) setTarget(null);
       }}
       channelName={target?.name ?? ""}
+      error={leaveChannel.error}
+      isPending={leaveChannel.isPending}
       onConfirm={() => {
         if (target) {
-          leaveChannel.mutate();
+          void leaveChannel.mutateAsync().then(() => {
+            setTarget(null);
+          });
         }
-        setTarget(null);
       }}
     />
   );
diff --git a/desktop/src/features/sidebar/ui/leaveChannelDialog.test.mjs b/desktop/src/features/sidebar/ui/leaveChannelDialog.test.mjs
new file mode 100644
index 0000000000..622bc244f2
--- /dev/null
+++ b/desktop/src/features/sidebar/ui/leaveChannelDialog.test.mjs
@@ -0,0 +1,136 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+/**
+ * Tests for the leave-channel dialog error-surfacing logic.
+ *
+ * These tests verify the decision logic that backs
+ * `useLeaveChannelDialog` — specifically that:
+ * - The dialog stays open when the mutation fails
+ * - The dialog closes only on successful mutation
+ * - The error message is surfaced to the user
+ * - Pending state prevents dismissal
+ */
+
+// Simulate the leave-channel dialog state machine
+function createLeaveDialogState() {
+  let target = null;
+  let isPending = false;
+  let error = null;
+
+  return {
+    get isOpen() {
+      return target !== null;
+    },
+    get error() {
+      return error;
+    },
+    get isPending() {
+      return isPending;
+    },
+    requestLeave(channel) {
+      target = channel;
+      error = null;
+    },
+    async confirm(mutateFn) {
+      if (!target) return;
+      isPending = true;
+      try {
+        await mutateFn();
+        target = null; // close on success
+      } catch (e) {
+        error = e; // keep open on failure
+      } finally {
+        isPending = false;
+      }
+    },
+    dismiss() {
+      if (!isPending) {
+        target = null;
+        error = null;
+      }
+    },
+  };
+}
+
+test("dialog stays open when leave mutation fails", async () => {
+  const dlg = createLeaveDialogState();
+  dlg.requestLeave({ id: "ch1", name: "Welcome" });
+  assert.equal(dlg.isOpen, true);
+
+  await dlg.confirm(async () => {
+    throw new Error("You are the only owner of this channel.");
+  });
+
+  assert.equal(dlg.isOpen, true, "Dialog should remain open on error");
+  assert.ok(dlg.error instanceof Error);
+  assert.match(dlg.error.message, /only owner/);
+});
+
+test("dialog closes when leave mutation succeeds", async () => {
+  const dlg = createLeaveDialogState();
+  dlg.requestLeave({ id: "ch2", name: "General" });
+  assert.equal(dlg.isOpen, true);
+
+  await dlg.confirm(async () => {
+    // success — no throw
+  });
+
+  assert.equal(dlg.isOpen, false, "Dialog should close on success");
+  assert.equal(dlg.error, null);
+});
+
+test("dismiss is blocked while mutation is pending", () => {
+  const dlg = createLeaveDialogState();
+  dlg.requestLeave({ id: "ch3", name: "Dev" });
+
+  // Simulate pending state
+  dlg.confirm(async () => {
+    return new Promise(() => {}); // never resolves
+  });
+
+  // Can't dismiss while pending
+  dlg.dismiss();
+  assert.equal(dlg.isOpen, true, "Dialog should not dismiss while pending");
+});
+
+test("dismiss works when not pending", () => {
+  const dlg = createLeaveDialogState();
+  dlg.requestLeave({ id: "ch4", name: "Test" });
+  assert.equal(dlg.isOpen, true);
+
+  dlg.dismiss();
+  assert.equal(dlg.isOpen, false);
+});
+
+test("error is cleared on a new leave request", async () => {
+  const dlg = createLeaveDialogState();
+  dlg.requestLeave({ id: "ch5", name: "Failed" });
+  await dlg.confirm(async () => {
+    throw new Error("You are the only owner.");
+  });
+  assert.ok(dlg.error instanceof Error);
+
+  // User tries to leave a different channel
+  dlg.requestLeave({ id: "ch6", name: "Other" });
+  assert.equal(dlg.error, null, "Error should be cleared on new request");
+});
+
+test("isPending is true during mutation and false after", async () => {
+  const dlg = createLeaveDialogState();
+  dlg.requestLeave({ id: "ch7", name: "Pending" });
+  assert.equal(dlg.isPending, false);
+
+  let resolveMutation;
+  const mutationPromise = new Promise((resolve) => {
+    resolveMutation = resolve;
+  });
+
+  const confirmPromise = dlg.confirm(() => mutationPromise);
+  assert.equal(dlg.isPending, true, "Should be pending during mutation");
+
+  resolveMutation();
+  await confirmPromise;
+
+  assert.equal(dlg.isPending, false, "Should not be pending after mutation");
+});