test: add P1-fallback + refresh tests for StudyHomeViewModel

- P1 fallback: continueService throws → falls to unfinished session
- refresh: updates stats without setting loadingState
- Fix: remove nonexistent materialId/readingTargetType from LearningSession mock

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

AIStudyApp/AIStudyAppTests/StudyHomeViewModelTests.swift

@@ -187,4 +187,31 @@ final class StudyHomeViewModelTests: XCTestCase {
         XCTAssertEqual(vm.weeklyActiveDays, 5)
         XCTAssertEqual(vm.streakDays, 3)
     }
+
+    // MARK: - P1 fallback: continueService throws → unfinished session
+
+    func test_priority_fallback_to_unfinished_session_when_continueService_throws() async {
+        mockContinue.response = nil // throws
+        mockSession.sessions = [LearningSession(
+            id: "s1", userId: nil, knowledgeBaseId: "kb1", knowledgeItemId: nil,
+            mode: nil, status: "in_progress", startedAt: "2026-01-02T00:00:00.000Z",
+            endedAt: nil, durationSeconds: nil, focusMinutes: nil, createdAt: nil
+        )]
+        mockKB.kbs = [KnowledgeBase(id: "kb1", title: "My KB", description: nil, knowledgeCount: 5, sourceCount: 1, userId: "u1", createdAt: "2026-01-01")]
+
+        await vm.loadAll()
+
+        guard case .continueSession = vm.mainAction else {
+            return XCTFail("Expected continueSession fallback, got \(String(describing: vm.mainAction))")
+        }
+    }
+
+    // MARK: - refresh()
+
+    func test_refresh_updates_review_count() async {
+        mockReview.cards = []
+        await vm.refresh()
+        XCTAssertEqual(vm.todayReviewCount, 0)
+        XCTAssertEqual(vm.loadingState, .idle) // refresh doesn't set loadingState
+    }
 }