diff --git a/apps/desktop/src/sdk/host-state.test.ts b/apps/desktop/src/sdk/host-state.test.ts
index ddbc314df2..1dd2590092 100644
--- a/apps/desktop/src/sdk/host-state.test.ts
+++ b/apps/desktop/src/sdk/host-state.test.ts
@@ -38,9 +38,9 @@ describe('host.state focused-session atoms', () => {
     for (const key of ['focusedSessionId', 'focusedStoredSessionId', 'focusedUsage'] as const) {
       const store = host.state[key]
       expect(store, key).toBeDefined()
-      expect(typeof store.get, 'function', key)
-      expect(typeof store.listen, 'function', key)
-      expect(typeof store.subscribe, 'function', key)
+      expect(typeof store.get, key).toBe('function')
+      expect(typeof store.listen, key).toBe('function')
+      expect(typeof store.subscribe, key).toBe('function')
     }
   })
 
@@ -74,6 +74,7 @@ describe('host.state focused-session atoms', () => {
         title: id
       })
     }
+
     tree.declareDefaultTree(
       model.split('row', [
         model.group(['workspace'], { active: 'workspace', id: 'grp-main' }),
diff --git a/apps/desktop/src/sdk/index.ts b/apps/desktop/src/sdk/index.ts
index 9a86fc3134..1d71e32287 100644
--- a/apps/desktop/src/sdk/index.ts
+++ b/apps/desktop/src/sdk/index.ts
@@ -145,8 +145,10 @@ export const host = {
     focusedStoredSessionId: readonlyAtom<null | string>($focusedStoredSessionId),
     /** Live usage snapshot of the focused session (`context_used` /
      *  `context_max` / `context_percent`, token counts, `cost_usd`) —
-     *  streamed by the backend, no RPC needed. Null while unresolved. */
-    focusedUsage: readonlyAtom<null | UsageStats>($focusedUsage),
+     *  streamed by the backend, no RPC needed. Null while unresolved.
+     *  Partial: the backend streams whichever fields changed, so every
+     *  field read needs a fallback. */
+    focusedUsage: readonlyAtom<null | Partial<UsageStats>>($focusedUsage),
     /** Gateway socket state: 'idle' | 'connecting' | 'open' | …. Not turn-busy. */
     gateway: readonlyAtom<string>($gatewayState),
     /** Current main model slug. */