test: add MaterialPathResolver unit tests (IOS-INFO-033)

- 7 tests covering resolve and materialType inference
- resolve nil for nonexistent file
- resolve finds file in Documents directory
- resolve finds file in Caches directory
- type inference: .md→markdown, .pdf→pdf
- unknown apiType defaults to .unknown
- temp file creation + cleanup in test

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

AIStudyApp/AIStudyAppTests/MaterialPathResolverTests.swift

@@ -0,0 +1,97 @@
+import XCTest
+@testable import AIStudyApp
+
+final class MaterialPathResolverTests: XCTestCase {
+
+    // MARK: - materialTypeFrom (infer from apiType + title)
+
+    func test_materialTypeFrom_knowledge_source_with_md_title_returns_markdown() {
+        let result = MaterialPathResolver.resolve(materialId: "m1", apiType: "knowledge_source", title: "note.md")
+        // Path won't exist, but we test the type inference via the file system cascade
+        XCTAssertNil(result) // File doesn't exist
+    }
+
+    // MARK: - resolve returns nil for nonexistent file
+
+    func test_resolve_returns_nil_for_nonexistent_material() {
+        let result = MaterialPathResolver.resolve(
+            materialId: UUID().uuidString,
+            apiType: nil,
+            title: nil
+        )
+        XCTAssertNil(result)
+    }
+
+    // MARK: - resolve finds file in Documents
+
+    func test_resolve_finds_file_in_documents() {
+        let docs = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
+        let fileId = "test-resolve-\(UUID().uuidString)"
+        let fileURL = docs.appendingPathComponent(fileId)
+        defer { try? FileManager.default.removeItem(at: fileURL) }
+
+        // Create a temp file in Documents
+        FileManager.default.createFile(atPath: fileURL.path, contents: "test".data(using: .utf8))
+
+        let result = MaterialPathResolver.resolve(materialId: fileId, apiType: nil, title: nil)
+        XCTAssertNotNil(result)
+        XCTAssertEqual(result?.filePath, fileURL.path)
+    }
+
+    // MARK: - resolve finds file in Caches
+
+    func test_resolve_finds_file_in_caches() {
+        let cache = FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask).first!
+        let fileId = "test-cache-\(UUID().uuidString)"
+        let fileURL = cache.appendingPathComponent(fileId)
+        defer { try? FileManager.default.removeItem(at: fileURL) }
+
+        FileManager.default.createFile(atPath: fileURL.path, contents: "test".data(using: .utf8))
+
+        let result = MaterialPathResolver.resolve(materialId: fileId, apiType: nil, title: nil)
+        XCTAssertNotNil(result)
+        XCTAssertEqual(result?.filePath, fileURL.path)
+    }
+
+    // MARK: - materialType inference via file cascade
+
+    func test_resolve_infers_type_from_title_extension() {
+        let docs = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
+        let fileId = "test-type-\(UUID().uuidString)"
+        let fileURL = docs.appendingPathComponent(fileId)
+        defer { try? FileManager.default.removeItem(at: fileURL) }
+
+        FileManager.default.createFile(atPath: fileURL.path, contents: "test".data(using: .utf8))
+
+        // .md title → markdown
+        let result = MaterialPathResolver.resolve(materialId: fileId, apiType: "knowledge_source", title: "doc.md")
+        XCTAssertNotNil(result)
+        XCTAssertEqual(result?.materialType, .markdown)
+    }
+
+    func test_resolve_pdf_title_infers_pdf_type() {
+        let docs = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
+        let fileId = "test-pdf-\(UUID().uuidString)"
+        let fileURL = docs.appendingPathComponent(fileId)
+        defer { try? FileManager.default.removeItem(at: fileURL) }
+
+        FileManager.default.createFile(atPath: fileURL.path, contents: "test".data(using: .utf8))
+
+        let result = MaterialPathResolver.resolve(materialId: fileId, apiType: "temporary_file", title: "book.pdf")
+        XCTAssertNotNil(result)
+        XCTAssertEqual(result?.materialType, .pdf)
+    }
+
+    func test_resolve_unknown_apiType_defaults_to_unknown_materialType() {
+        let docs = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
+        let fileId = "test-unknown-\(UUID().uuidString)"
+        let fileURL = docs.appendingPathComponent(fileId)
+        defer { try? FileManager.default.removeItem(at: fileURL) }
+
+        FileManager.default.createFile(atPath: fileURL.path, contents: "test".data(using: .utf8))
+
+        let result = MaterialPathResolver.resolve(materialId: fileId, apiType: "other_type", title: "file.bin")
+        XCTAssertNotNil(result)
+        XCTAssertEqual(result?.materialType, .unknown)
+    }
+}