diff --git a/src/renderer/components/sidebar/DateGroupedSessions.tsx b/src/renderer/components/sidebar/DateGroupedSessions.tsx
index f55b1f24..b2d99211 100644
--- a/src/renderer/components/sidebar/DateGroupedSessions.tsx
+++ b/src/renderer/components/sidebar/DateGroupedSessions.tsx
@@ -38,6 +38,7 @@ import { useShallow } from 'zustand/react/shallow';
 import { WorktreeBadge } from '../common/WorktreeBadge';
 import { Combobox, type ComboboxOption } from '../ui/combobox';
 
+import { resolveEffectiveSelectedRepositoryId } from './dateGroupedSessionsSelection';
 import { SESSION_PROVIDER_IDS, SessionFiltersPopover } from './SessionFiltersPopover';
 import { SessionItem } from './SessionItem';
 
@@ -327,21 +328,15 @@ export const DateGroupedSessions = (): React.JSX.Element => {
 
   const effectiveSelectedWorktreeId =
     selectedWorktreeId ?? activeProjectId ?? selectedProjectId ?? null;
-  const effectiveSelectedRepositoryId = useMemo(() => {
-    if (selectedRepositoryId) {
-      return selectedRepositoryId;
-    }
-
-    if (!effectiveSelectedWorktreeId) {
-      return null;
-    }
-
-    return (
-      repositoryGroups.find((repo) =>
-        repo.worktrees.some((worktree) => worktree.id === effectiveSelectedWorktreeId)
-      )?.id ?? null
-    );
-  }, [effectiveSelectedWorktreeId, repositoryGroups, selectedRepositoryId]);
+  const effectiveSelectedRepositoryId = useMemo(
+    () =>
+      resolveEffectiveSelectedRepositoryId({
+        repositoryGroups,
+        selectedRepositoryId,
+        effectiveSelectedWorktreeId,
+      }),
+    [effectiveSelectedWorktreeId, repositoryGroups, selectedRepositoryId]
+  );
 
   const activeProjectValue =
     viewMode === 'grouped'
diff --git a/src/renderer/components/sidebar/dateGroupedSessionsSelection.ts b/src/renderer/components/sidebar/dateGroupedSessionsSelection.ts
new file mode 100644
index 00000000..4c0e806d
--- /dev/null
+++ b/src/renderer/components/sidebar/dateGroupedSessionsSelection.ts
@@ -0,0 +1,27 @@
+import type { RepositoryGroup } from '@renderer/types/data';
+
+interface ResolveEffectiveSelectedRepositoryIdInput {
+  repositoryGroups: readonly RepositoryGroup[];
+  selectedRepositoryId: string | null;
+  effectiveSelectedWorktreeId: string | null;
+}
+
+export function resolveEffectiveSelectedRepositoryId({
+  repositoryGroups,
+  selectedRepositoryId,
+  effectiveSelectedWorktreeId,
+}: ResolveEffectiveSelectedRepositoryIdInput): string | null {
+  if (selectedRepositoryId) {
+    return selectedRepositoryId;
+  }
+
+  if (!effectiveSelectedWorktreeId) {
+    return null;
+  }
+
+  return (
+    repositoryGroups.find((repo) =>
+      repo.worktrees.some((worktree) => worktree.id === effectiveSelectedWorktreeId)
+    )?.id ?? null
+  );
+}
diff --git a/test/renderer/components/sidebar/dateGroupedSessionsSelection.test.ts b/test/renderer/components/sidebar/dateGroupedSessionsSelection.test.ts
new file mode 100644
index 00000000..63fda15d
--- /dev/null
+++ b/test/renderer/components/sidebar/dateGroupedSessionsSelection.test.ts
@@ -0,0 +1,53 @@
+import { describe, expect, it } from 'vitest';
+
+import { resolveEffectiveSelectedRepositoryId } from '../../../../src/renderer/components/sidebar/dateGroupedSessionsSelection';
+
+describe('resolveEffectiveSelectedRepositoryId', () => {
+  it('falls back to the repository that owns the active worktree when repository selection is empty', () => {
+    const repositoryGroups = [
+      {
+        id: 'repo-headless',
+        worktrees: [
+          {
+            id: 'worktree-headless',
+            path: '/Users/belief/dev/projects/headless',
+          },
+        ],
+      },
+      {
+        id: 'repo-other',
+        worktrees: [
+          {
+            id: 'worktree-other',
+            path: '/Users/belief/dev/projects/other',
+          },
+        ],
+      },
+    ] as const;
+
+    expect(
+      resolveEffectiveSelectedRepositoryId({
+        repositoryGroups,
+        selectedRepositoryId: null,
+        effectiveSelectedWorktreeId: 'worktree-headless',
+      })
+    ).toBe('repo-headless');
+  });
+
+  it('keeps the explicit repository selection when it already exists', () => {
+    const repositoryGroups = [
+      {
+        id: 'repo-headless',
+        worktrees: [{ id: 'worktree-headless', path: '/Users/belief/dev/projects/headless' }],
+      },
+    ] as const;
+
+    expect(
+      resolveEffectiveSelectedRepositoryId({
+        repositoryGroups,
+        selectedRepositoryId: 'repo-headless',
+        effectiveSelectedWorktreeId: 'worktree-headless',
+      })
+    ).toBe('repo-headless');
+  });
+});