diff --git a/tests/unit/backend.test.js b/tests/unit/backend.test.js
index 4ee892f..1e51818 100644
--- a/tests/unit/backend.test.js
+++ b/tests/unit/backend.test.js
@@ -142,6 +142,19 @@ describe('getVersionData', () => {
     expect(result.error).toBeTruthy();
   });
 
+  // Ref: #107 — L542-543 branch: empty history sheet (lastRow < 2)
+  it('returns not-found when history sheet is empty (no data rows)', () => {
+    const historySheet = createMockSheet('History', {
+      A1: 'Timestamp', B1: 'SavedBy', C1: 'Data',
+      // No data rows — lastRow will be 1 (header only)
+    });
+    const gas = createGasEnv({ sheets: { History: historySheet } });
+
+    const result = gas.getVersionData('2024-01-01T00:00:00.000Z');
+    expect(result.success).toBe(false);
+    expect(result.error).toContain('找不到');
+  });
+
   it('skips invalid date rows without crashing (Ref: #39)', () => {
     const validTs = '2024-06-15T10:30:00.000Z';
     const historySheet = createMockSheet('History', {
@@ -257,6 +270,28 @@ describe('copySchedule', () => {
     expect(result.newId).toMatch(/^schedule_/);
     expect(result.createdBy).toBe('owner@school.com');
   });
+
+  // Ref: #107 — L458 branch: sourceId not found in Data index
+  it('returns error when source schedule not found in Data index', () => {
+    const ts = '2024-01-01T00:00:00.000Z';
+    const dataSheet = createMockSheet('Data', {
+      A1: 'ID', B1: 'Name', C1: 'Modified', D1: 'CreatedBy',
+      F1: ts,
+      A2: 'schedule_1', B2: 'Existing', C2: ts, D2: 'owner@test.com',
+    });
+    const gas = createGasEnv({
+      userEmail: 'owner@test.com',
+      scriptProps: { ADMIN_EMAIL: 'admin@test.com' },
+      sheets: { Data: dataSheet },
+    });
+    const result = gas.copySchedule({
+      sourceId: 'schedule_nonexistent',
+      newName: 'Copy',
+      metadataTimestamp: ts,
+    });
+    expect(result.success).toBe(false);
+    expect(result.error).toContain('找不到來源課表');
+  });
 });
 
 // ─── getData ─────────────────────────────────────────────────────────────
diff --git a/vitest.config.js b/vitest.config.js
index c17c24d..8175524 100644
--- a/vitest.config.js
+++ b/vitest.config.js
@@ -19,12 +19,12 @@ export default defineConfig({
       // production JS surface. See #110 for details.
       include: ['程式碼.js', 'tests/lib/**/*.js'],
       thresholds: {
-        // Ratcheted from 55/65/75/55 to actual values minus ~3% buffer (#107 P0).
-        // Actuals at time of ratchet (2026-06-24): Stmts 70.71%, Branch 77.38%, Funcs 84.94%, Lines 70.06%.
-        lines: 67,
-        functions: 82,
-        branches: 74,
-        statements: 67,
+        // Re-ratcheted from 67/74/82/67 after backend branch gap fill (#107 P1).
+        // Actuals (2026-06-24): Stmts ~98%, Branch ~93%, Funcs ~98%, Lines ~99%.
+        lines: 95,
+        functions: 95,
+        branches: 90,
+        statements: 95,
       },
     },
   },