Module Update

docs/architecture/002_exam_structure_migration.md

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+# Database Schema Change Request: Exam Structure Support
+
+## 1. Table: `exams`
+
+### Change
+**Add Column**: `structure`
+
+### Details
+- **Type**: `JSON`
+- **Nullable**: `TRUE` (Default: `NULL`)
+
+### Reason
+To support hierarchical exam structures (e.g., Sections/Groups containing Questions). The existing flat `exam_questions` table only supports a simple list of questions and is insufficient for complex exam layouts (e.g., "Part A: Reading", "Part B: Writing").
+
+### Before vs After
+
+**Before**:
+`exams` table only stores metadata (`title`, `description`, etc.). Question ordering relies solely on `exam_questions.order`.
+
+**After**:
+`exams` table includes `structure` column to store the full tree representation:
+```json
+[
+  { "id": "uuid-1", "type": "group", "title": "Section A", "children": [...] },
+  { "id": "uuid-2", "type": "question", "questionId": "q1", "score": 10 }
+]
+```
+*Note: `exam_questions` table is retained for relational integrity and efficient querying of question usage, but the presentation order/structure is now driven by this new JSON column.*
+
+---
+
+## 2. Table: `questions_to_knowledge_points`
+
+### Change
+**Rename Foreign Key Constraints**
+
+### Details
+- Rename constraint for `question_id` to `q_kp_qid_fk`
+- Rename constraint for `knowledge_point_id` to `q_kp_kpid_fk`
+
+### Reason
+The default generated foreign key names (e.g., `questions_to_knowledge_points_knowledge_point_id_knowledge_points_id_fk`) exceed the MySQL identifier length limit (64 characters), causing migration failures.
+
+### Before vs After
+
+**Before**:
+- FK Name: `questions_to_knowledge_points_question_id_questions_id_fk` (Too long)
+- FK Name: `questions_to_knowledge_points_knowledge_point_id_knowledge_points_id_fk` (Too long)
+
+**After**:
+- FK Name: `q_kp_qid_fk`
+- FK Name: `q_kp_kpid_fk`