[CLAUDE] Phase2: Form Engine MVP + docs (gotchas, skill, handoff)

Backend Forms:
- Domain/Forms: ContractTemplate (FormCode, Name, ContractType, FileName, StoragePath, Format, FieldSpec JSON, IsActive) + ContractClause
- EF config voi unique FormCode + query filter IsDeleted
- DbSets + IApplicationDbContext update
- Migration AddForms (bang 14 total)
- Packages: DocumentFormat.OpenXml 3.x + ClosedXML 0.105+
- Application/Forms:
  - IFormRenderer interface + RenderResult record
  - FormFeatures.cs: List/Get/Render CQRS
  - IWebHostEnvironmentLocator (abstract IWebHostEnvironment)
- Infrastructure/Forms:
  - DocxRenderer: OpenXml-based placeholder {{field}} replace, handle split runs (gom text tat ca <w:t> trong paragraph, replace, gan lai text dau + clear rest)
  - XlsxRenderer: ClosedXML cell value replace
  - FormRenderer router theo format docx/xlsx
- Api:
  - FormsController: GET /templates (filter type, onlyActive), GET /templates/{id}, POST /templates/{id}/render (return file)
  - WebHostEnvironmentLocator impl
- DbInitializer SeedContractTemplatesAsync: seed 8 template metadata, IsActive=true chi khi file ton tai

Templates vat ly:
- Copy 5 .docx/.xlsx tu FORM/ sang wwwroot/templates/
- 3 .doc (FO-002.02/03/06) chua convert: IsActive=false (Word COM bi stuck luc test, can retry voi DisplayAlerts=0 hoac LibreOffice)
- scripts/convert-doc-to-docx.ps1 (Word COM automation)

Frontend fe-admin:
- types/forms.ts: ContractTemplate + ContractTypeLabel
- pages/forms/FormsPage.tsx: list templates + Render dialog (paste JSON data → download .docx/.xlsx)
- Route /forms them vao App.tsx

Bug fix:
- SpaceProcessingModeValues namespace: wrap EnumValue<> full path
- SaveAs2($path, 16) thay vi SaveAs([ref], [ref]) — PowerShell type issue
- Word COM stuck: kill process, skip .doc cho MVP

Docs (theo yeu cau user):
- docs/gotchas.md MOI: 17 pitfalls nhom theo tech stack / EF Core / OpenXml / JSON / dev workflow
- .claude/skills/form-engine/SKILL.md: placeholder → full spec (algorithm + code pointers + API + limitations)
- .claude/skills/permission-matrix/SKILL.md: placeholder → full spec (BE policy + FE guard + seed + pitfalls)
- docs/HANDOFF.md MOI: brief 5 phut cho session sau (run quickstart + where we are + next steps + file tree + gotchas ref)
- docs/STATUS.md: update cumulative stats + next up Phase 3
- docs/changelog/migration-todos.md: tick Phase 2 iteration 1 items + add iteration 2 list
- docs/changelog/sessions/2026-04-21-1200-phase2-form-engine.md: session log
- CLAUDE.md root: them reference den gotchas + HANDOFF

E2E verified:
- GET /api/forms/templates (onlyActive=false) → 8 templates
- POST /api/forms/templates/{FO-002.05}/render voi data dict → HTTP 200 + file .docx 482KB (Microsoft Word 2007+ OK)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Backend/SolutionErp.Domain/Forms/ContractClause.cs

@@ -0,0 +1,13 @@
+using SolutionErp.Domain.Common;
+
+namespace SolutionErp.Domain.Forms;
+
+// Điều khoản chung (vd FO-002.04) — đính kèm appendix cho HĐ trọn gói. Admin edit qua rich text.
+public class ContractClause : AuditableEntity
+{
+    public string Code { get; set; } = string.Empty;         // vd "FO-002.04"
+    public string Name { get; set; } = string.Empty;
+    public string Content { get; set; } = string.Empty;      // rich text (HTML/Markdown)
+    public int Version { get; set; } = 1;
+    public bool IsActive { get; set; } = true;
+}

src/Backend/SolutionErp.Domain/Forms/ContractTemplate.cs

@@ -0,0 +1,18 @@
+using SolutionErp.Domain.Common;
+using SolutionErp.Domain.Contracts;
+
+namespace SolutionErp.Domain.Forms;
+
+// Mapping 1 mẫu HĐ (file .docx hoặc .xlsx trong wwwroot/templates) → metadata + field spec JSON
+public class ContractTemplate : AuditableEntity
+{
+    public string FormCode { get; set; } = string.Empty;      // vd "SOL-CCM-FO-002.05"
+    public string Name { get; set; } = string.Empty;          // vd "Hợp đồng Giao khoán"
+    public ContractType? ContractType { get; set; }           // null nếu đây là phụ lục (điều kiện chung)
+    public string FileName { get; set; } = string.Empty;      // tên file gốc (để preserve extension)
+    public string StoragePath { get; set; } = string.Empty;   // relative path dưới wwwroot/templates/
+    public string Format { get; set; } = "docx";              // "docx" | "xlsx"
+    public string? FieldSpec { get; set; }                    // JSON field spec — null nếu chưa định nghĩa
+    public bool IsActive { get; set; } = true;
+    public string? Description { get; set; }
+}