diff --git a/apps/web/src/components/Sidebar.logic.test.ts b/apps/web/src/components/Sidebar.logic.test.ts
index 3e2e8be2ce18d..88de6144a7ec9 100644
--- a/apps/web/src/components/Sidebar.logic.test.ts
+++ b/apps/web/src/components/Sidebar.logic.test.ts
@@ -636,7 +636,28 @@ describe("getFallbackThreadIdAfterDelete", () => {
       { snoozedUntil: "2099-01-01T00:00:00.000Z", snoozedAt: "2026-03-09T10:06:00.000Z" },
     ],
     ["settled", { settledOverride: "settled", settledAt: "2026-03-09T10:06:00.000Z" }],
-  ] as const)("skips a %s thread parked on its shelf", (_state, parked) => {
+    [
+      "side chat",
+      {
+        lineage: {
+          rootThreadId: ThreadId.make("thread-visible"),
+          parentThreadId: ThreadId.make("thread-visible"),
+          relationshipToParent: "fork",
+          sideChat: true,
+        },
+      },
+    ],
+    [
+      "subagent",
+      {
+        lineage: {
+          rootThreadId: ThreadId.make("thread-visible"),
+          parentThreadId: ThreadId.make("thread-visible"),
+          relationshipToParent: "subagent",
+        },
+      },
+    ],
+  ] as const)("skips a %s thread the sidebar does not list", (_state, parked) => {
     const fallbackThreadId = getFallbackThreadIdAfterDelete({
       threads: [
         makeThread({
diff --git a/apps/web/src/components/Sidebar.logic.ts b/apps/web/src/components/Sidebar.logic.ts
index c20789e2a9160..6b006352fabaa 100644
--- a/apps/web/src/components/Sidebar.logic.ts
+++ b/apps/web/src/components/Sidebar.logic.ts
@@ -1211,7 +1211,10 @@ export function resolveThreadStatusPill(input: {
 }
 
 export function getFallbackThreadIdAfterDelete<
-  T extends Pick<Thread, "id" | "projectId" | "createdAt" | "updatedAt" | "settledOverride"> &
+  T extends Pick<
+    Thread,
+    "id" | "projectId" | "createdAt" | "updatedAt" | "settledOverride" | "lineage"
+  > &
     ThreadSortInput &
     ThreadSnoozeShell,
 >(input: {
@@ -1235,7 +1238,8 @@ export function getFallbackThreadIdAfterDelete<
           thread.id !== deletedThreadId &&
           !deletedThreadIds?.has(thread.id) &&
           thread.settledOverride !== "settled" &&
-          !effectiveSnoozed(thread, { now }),
+          !effectiveSnoozed(thread, { now }) &&
+          !isSidebarHiddenThread(thread),
       ),
       sortOrder,
     )[0]?.id ?? null