Add App.StartScreen guidance to canvas-apps guide and planner agent

Agent-Logs-Url: https://github.com/microsoft/power-platform-skills/sessions/265fed62-a281-4022-a4be-d524079545aa

Co-authored-by: lesaltzm <69215460+lesaltzm@users.noreply.github.com>

Author: Copilot

plugins/canvas-apps/agents/canvas-app-planner.md

@@ -114,6 +114,15 @@ Write the app-level YAML file (`App.pa.yaml`) to the working directory. This fil
 across all screens — do not write screen-level content here. Follow TechnicalGuide.md
 conventions for app-level properties.
 
+Set `App.StartScreen` to the intended initial landing screen of the app so it opens on the
+correct screen when launched. For example:
+
+```yaml
+App:
+  Properties:
+    StartScreen: =HomeScreen
+```
+
 ## Step 7 — Write canvas-app-plan.md
 
 Write `canvas-app-plan.md` to the working directory. This document is the **single source of

plugins/canvas-apps/references/TechnicalGuide.md

@@ -39,6 +39,14 @@ Screens:
                 ...
 ```
 
+> **Note:** Always set `App.StartScreen` in `App.pa.yaml` to the screen that should be shown when the app launches. Without it, the app may open on an unexpected screen.
+>
+> ```yaml
+> App:
+>   Properties:
+>     StartScreen: =HomeScreen
+> ```
+
 ## YAML Syntax Rules
 
 ### Multi-line formulas — use `|-`
@@ -368,6 +376,9 @@ App:
 
 ## Best Practices
 
+### App Configuration
+- ✅ Set `App.StartScreen` to the initial landing screen so the app always opens on the intended screen
+
 ### State Management
 - ✅ Initialize all variables in `OnVisible`
 - ✅ Use descriptive variable names