feat: refine native iOS chat experience

Tests/ChatTests.swift

@@ -35,6 +35,31 @@ final class ChatTests: XCTestCase {
         XCTAssertNil(store.selected)
         XCTAssertTrue(store.messages.isEmpty)
     }
+    func testWorkspaceSaveReportsFailureAndPreservesExistingWorkspaces() async throws {
+        let store = ChatStore(api: OfflineChatAPI())
+        let rejected = await store.saveWorkspace(nil, name: "   ", instructions: "Ignored")
+        XCTAssertFalse(rejected)
+        XCTAssertEqual(store.error, "Enter a workspace name.")
+        XCTAssertTrue(store.workspaces.isEmpty)
+        let saved = await store.saveWorkspace(nil, name: "Writing", instructions: "Be concise")
+        XCTAssertTrue(saved)
+        XCTAssertEqual(store.workspaces.map(\.name), ["Writing"])
+    }
+    func testPreviewClearsOldContentBeforeNewRequestAndOnTeardown() async throws {
+        let api = OfflineChatAPI()
+        let store = ChatStore(api: api)
+        await store.features.load()
+        let data = Data("Private preview".utf8)
+        _ = await store.features.upload(data, filename: "preview.txt", mime: "text/plain")
+        let attachment = try XCTUnwrap(store.features.attachments.first)
+        store.features.previewText = "stale"
+        await store.features.preview(attachment)
+        XCTAssertEqual(store.features.previewAttachment?.id, attachment.id)
+        XCTAssertNotEqual(store.features.previewText, "stale")
+        store.features.clearPreview()
+        XCTAssertNil(store.features.previewAttachment)
+        XCTAssertNil(store.features.previewText)
+    }
     func testOfflineResearchTruthfulExportAndTeardown() async throws {
         let store = ChatStore(api: OfflineChatAPI())
         await store.create()