Module Update

docs/db/schema-changelog.md

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+# Database Schema Changelog
+
+## v1.1.0 - Exam Structure & Performance Optimization
+**Date:** 2025-12-29  
+**Migration ID:** `0001_flawless_texas_twister`  
+**Author:** Principal Database Architect
+
+### 1. Summary
+This release introduces support for hierarchical exam structures (Sectioning/Grouping) and optimizes database constraint naming for better compatibility with MySQL environments.
+
+### 2. Changes
+
+#### 2.1 Table: `exams`
+*   **Action**: `ADD COLUMN`
+*   **Field**: `structure` (JSON)
+*   **Reason**: To support nested exam layouts (e.g., "Part I: Listening", "Section A").
+    *   *Architecture Note*: This JSON field is strictly for **Presentation Layer** ordering and grouping. The `exam_questions` table remains the **Source of Truth** for relational integrity and scoring logic.
+    *   **Schema Definition**:
+        ```typescript
+        type ExamStructure = Array<
+           | { type: 'group', title: string, children: ExamStructure }
+           | { type: 'question', questionId: string, score: number }
+        >
+        ```
+
+#### 2.2 Table: `questions_to_knowledge_points`
+*   **Action**: `RENAME FOREIGN KEY`
+*   **Details**:
+    *   Old: `questions_to_knowledge_points_question_id_questions_id_fk` -> New: `q_kp_qid_fk`
+    *   Old: `questions_to_knowledge_points_knowledge_point_id_knowledge_points_id_fk` -> New: `q_kp_kpid_fk`
+*   **Reason**: Previous names exceeded MySQL's 64-character identifier limit, causing potential migration failures in production environments.
+
+### 3. Migration Strategy
+*   **Up**: Run standard Drizzle migration. The script includes `ALTER TABLE ... DROP FOREIGN KEY` followed by `ADD CONSTRAINT`.
+*   **Down**: Revert `structure` column. Note that FK names can be kept short as they are implementation details.
+
+### 4. Impact Analysis
+*   **Performance**: Negligible. JSON parsing is done client-side or at application layer.
+*   **Data Integrity**: High. Existing data is unaffected. New `structure` field defaults to `NULL`.