fix: use sendHostContextChange for partial update accumulation test

Address PR review feedback: The test was using setHostContext with full
context spreads which didn't clearly demonstrate partial update
accumulation. Now uses sendHostContextChange directly to send truly
partial updates (only theme, then only viewport), making it clear
the App correctly merges multiple partial notifications.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: ochafik

src/app-bridge.test.ts

@@ -337,19 +337,18 @@ describe("App <-> AppBridge integration", () => {
       await newBridge.connect(newBridgeTransport);
       await newApp.connect(newAppTransport);
 
-      // Update only theme
-      newBridge.setHostContext({ ...initialContext, theme: "dark" });
+      // Send partial update: only theme changes
+      newBridge.sendHostContextChange({ theme: "dark" });
       await flush();
 
-      // Update viewport
-      newBridge.setHostContext({
-        theme: "dark",
-        locale: "en-US",
-        viewport: { width: 1024, height: 768 },
-      });
+      // Send another partial update: only viewport changes
+      newBridge.sendHostContextChange({ viewport: { width: 1024, height: 768 } });
       await flush();
 
-      // getHostContext should have all updates merged
+      // getHostContext should have accumulated all updates:
+      // - locale from initial (unchanged)
+      // - theme from first partial update
+      // - viewport from second partial update
       const context = newApp.getHostContext();
       expect(context?.theme).toBe("dark");
       expect(context?.locale).toBe("en-US");