feat: ClientScript Phase 2 — PostBack + ScriptManager shims

.squad/agents/jubilee/history.md

@@ -473,3 +473,16 @@ This wave establishes **documentation patterns** that will guide future control
 - **Page uses `@inject ClientScriptShim ClientScript`** — injected as scoped service. Calls `FlushAsync(JS)` in `OnAfterRenderAsync` since the page doesn't inherit BaseWebFormsComponent.
 - **Pattern:** Source code section at bottom showing complete `@code` block with escaped `@@` directives for display. Follows established migration demo conventions.
 - **Build verified:** 0 errors, pre-existing BL0005 warnings only.
+
+### PostBack & ScriptManager Demo Page (ClientScript Phase 2)
+
+- **Created** `samples/AfterBlazorServerSide/Components/Pages/ControlSamples/PostBackDemo/Index.razor` — three-section demo page for Phase 2 ClientScript postback shims.
+- **Section 1: GetPostBackEventReference** — button with `onclick="@_postBackScript"` fires `__doPostBack` from JS. PostBack event on WebFormsPageBase receives it server-side. Stable IDs: `postback-button`, `postback-script`, `postback-result`.
+- **Section 2: GetPostBackClientHyperlink** — anchor `href="@_postBackHyperlink"` triggers postback via `javascript:__doPostBack(...)` URL. Stable IDs: `postback-link`, `hyperlink-script`, `hyperlink-result`.
+- **Section 3: ScriptManager.GetCurrent** — uses `ScriptManagerShim.GetCurrent(this)` to register startup script that writes into `#scriptmanager-target`. Same Web Forms code pattern.
+- **Source Code section** at bottom with escaped `@@` directives.
+- **Inherits WebFormsPageBase** (not `@inject`) — gives access to `ClientScript`, `PostBack` event, and `ScriptManagerShim.GetCurrent(this)`. This differs from the ClientScriptShim demo which uses `@inject`.
+- **Updated** `ComponentCatalog.cs` — added "PostBack Demo" entry in "Migration Helpers" category after "IsPostBack".
+- **Updated** `ComponentList.razor` — added PostBack & ScriptManager link in Migration Helpers section.
+- **Build verified:** 0 errors, pre-existing BL0005 warnings only.
+- **Lesson:** Pages that need the PostBack event must `@inherits WebFormsPageBase`. The ClientScript property is available via inheritance (no separate `@inject` needed). `OnAfterRenderAsync` in WebFormsPageBase handles `FlushAsync` automatically.

docs/Analyzers/BWFC022.md

@@ -78,7 +78,7 @@ If you prefer to modernize your code now, rewrite to `IJSRuntime` directly. The
 | `RegisterStartupScript()` | `ClientScriptShim` (⭐ Easy) or `OnAfterRenderAsync()` + `IJSRuntime` (⭐⭐ Moderate) | ⭐ Easy |
 | `RegisterClientScriptInclude()` | `ClientScriptShim` (⭐ Easy) or `<script>` tag in layout (⭐ Easy) | ⭐ Easy |
 | `RegisterClientScriptBlock()` | `ClientScriptShim` (⭐ Easy) or JS module (⭐ Easy) | ⭐ Easy |
-| `GetPostBackEventReference()` | `@onclick` or `EventCallback<T>` | ⭐⭐ Medium |
+| `GetPostBackEventReference()` | `ClientScriptShim` (⭐ Easy — Phase 2) or `@onclick` / `EventCallback<T>` (⭐⭐ Medium) | ⭐ Easy |
 
 ### Common Fix: Startup Script
 
@@ -144,7 +144,17 @@ If you prefer to modernize your code now, rewrite to `IJSRuntime` directly. The
     }
     ```
 
-=== "Blazor (After)"
+=== "Blazor (After — Phase 2 with Shim, Zero Rewrite)"
+    ```csharp
+    // Same code works! ClientScriptShim returns __doPostBack() string
+    public string GetDeleteButtonScript()
+    {
+        return ClientScript.GetPostBackEventReference(
+            new PostBackOptions(btnDelete, "clicked"));
+    }
+    ```
+
+=== "Blazor (Modern Approach)"
     ```razor
     <button @onclick="HandleDelete">Delete</button>
 

docs/Analyzers/BWFC024.md

@@ -11,12 +11,14 @@
 
 This analyzer warns when you use `ScriptManager` code-behind methods like `GetCurrent()`, `SetFocus()`, `RegisterAsyncPostBackControl()`, and similar — Web Forms APIs for managing client scripts and UpdatePanel behavior.
 
+**Note:** Phase 2 now includes support for `GetCurrent()` and script registration methods via `ScriptManagerShim`. Methods like `SetFocus()` and `RegisterAsyncPostBackControl()` still require modernization.
+
 **Detected patterns:**
-- `ScriptManager.GetCurrent(Page)` / `ScriptManager.GetCurrent(this)`
-- `.SetFocus(control)`
-- `.RegisterAsyncPostBackControl(control)`
-- `.RegisterUpdateProgress(...)`
-- `.RegisterPostBackControl(...)`
+- `ScriptManager.GetCurrent(Page)` / `ScriptManager.GetCurrent(this)` — ✅ Phase 2 supported
+- `.SetFocus(control)` — ❌ Still requires JS interop
+- `.RegisterAsyncPostBackControl(control)` — ❌ Still requires component binding
+- `.RegisterUpdateProgress(...)` — ❌ Still requires component state
+- `.RegisterPostBackControl(...)` — ❌ Not supported
 
 ---
 
@@ -60,7 +62,36 @@ These methods have **no direct equivalents**. Each requires a different approach
 
 ## How to Fix
 
-The fix depends on **which** ScriptManager method you're using.
+The fix depends on **which** ScriptManager method you're using and which Phase you're in.
+
+### ✅ Phase 2: GetCurrent() and Script Registration Methods
+
+`ScriptManager.GetCurrent()` now returns a working `ScriptManagerShim` that delegates to `ClientScriptShim`.
+
+=== "Web Forms (Before)"
+    ```csharp
+    protected void Page_Load(object sender, EventArgs e)
+    {
+        ScriptManager sm = ScriptManager.GetCurrent(Page);
+        sm.RegisterStartupScript(this.GetType(), "init", "initPage();", true);
+    }
+    ```
+
+=== "Blazor (After — Phase 2, Zero Rewrite)"
+    ```csharp
+    protected override void OnInitialized()
+    {
+        // Same code works! ScriptManagerShim returns the component's ClientScriptShim
+        ScriptManager sm = ScriptManager.GetCurrent(this);
+        sm.RegisterStartupScript(this.GetType(), "init", "initPage();", true);
+    }
+    ```
+
+---
+
+### Still Requiring Modernization
+
+Other ScriptManager methods still require refactoring. See the fixes below.
 
 ### Fix 1: SetFocus() → JavaScript Interop
 
@@ -245,7 +276,7 @@ await module.InvokeVoidAsync("focusElement", searchBox);
 
 | Web Forms Method | Blazor Equivalent | Approach |
 |---|---|---|
-| `GetCurrent(Page)` | — | Remove; use component state |
+| `GetCurrent(Page)` | `ScriptManager.GetCurrent(this)` (Phase 2 — Zero Rewrite) | Easy |
 | `.SetFocus(control)` | `JS.InvokeVoidAsync("focus", @ref)` | JavaScript interop |
 | `.RegisterAsyncPostBackControl()` | Component parameter binding | Remove; use `@bind` or `EventCallback` |
 | `.RegisterPostBackControl()` | — | Remove; not needed in Blazor |