feat: Phase 3 — Event handler wiring & DataBind pattern conversion (GAP-09, GAP-32)

[csharpfritz]

Summary

Phase 3 of the migration automation initiative, adding two critical L1 script transforms that Forge's analysis identified as eliminating ~70% of remaining manual migration work.

What's New

🎯 Event Handler Wiring (GAP-32) — "Make event binding compile"

Adds @ prefix to event handler attributes in markup so Blazor's Razor compiler resolves method references correctly:

<!-- Before (Phase 2 output) -->
<Button id="btnSave" Text="Save" OnClick="Save_Click" />

<!-- After (Phase 3) -->
<Button id="btnSave" Text="Save" OnClick="@Save_Click" />

• New function: Convert-EventHandlerWiring
• Regex-safe: only targets On[A-Z]* attributes with bare C# identifiers
• Handles all event types: OnClick, OnTextChanged, OnSelectedIndexChanged, OnRowCommand, etc.

📊 DataBind Pattern Conversion (GAP-09) — "Make data binding work"

Cross-file transform that converts the DataSource/DataBind() pattern to Blazor's reactive Items binding:

Code-behind:

// Before
gvProducts.DataSource = GetProducts();
gvProducts.DataBind();

// After (generated)
private IEnumerable<object> _gvProductsData;
_gvProductsData = GetProducts();

Markup (correlated by control ID):

<!-- Before -->
<GridView id="gvProducts" />

<!-- After -->
<GridView id="gvProducts" Items="@_gvProductsData" />

New functions:

• Get-DataBindMap — Pre-scans code-behind for cross-file correlation
• Convert-DataBindPattern — Code-behind field generation + DataSource/DataBind removal
• Add-DataBindItemsAttribute — Markup Items attribute injection

Test Results

25/25 L1 tests pass (100%) — 618/618 lines match

Test	Description
TC22	DataBind with GridView (Page_Load → OnInitializedAsync + Items binding)
TC23	DataBind with multiple controls (GridView + Repeater)
TC24	Event wiring with 4 event types
TC25	Combined — DataBind + event wiring on same page
TC20/TC21	Updated expected output for @ prefix

Documentation

• docs/Migration/Phase3-EventHandlerWiring.md
• docs/Migration/Phase3-DataBindConversion.md
• mkdocs.yml — Phase 3 section added
• CODE-TRANSFORMS.md — Phase 3 patterns added