make some overall QoL improvements

test/attachmentComposer.test.js

@@ -97,3 +97,32 @@ test("discarding a chat draft aborts upload, deletes temporary files, and serial
     composer.clear();
     assert.deepEqual(deletes, [`/attachments/${temporaryId}`], "Sent attachments are retained");
 });
+
+test("attachments stay with their chat while uploads finish after switching", async t => {
+    const originalDocument = globalThis.document, originalFetch = globalThis.fetch;
+    t.after(() => { globalThis.document = originalDocument; globalThis.fetch = originalFetch; });
+    const elements = Object.fromEntries(["attachImage", "imagePicker", "uploadPreviews", "composer"].map(id => [id, new Element()]));
+    globalThis.document = {getElementById: id => elements[id], querySelector: () => elements.composer, createElement: () => new Element()};
+    let completeUpload;
+    const deletes = [];
+    globalThis.fetch = (url) => {
+        if (url === "/uploads/config") return Promise.resolve(Response.json({maxFiles: 5, maxSizeMb: 10}));
+        if (url === "/uploads") return new Promise(resolve => { completeUpload = resolve; });
+        deletes.push(url);
+        return Promise.resolve(Response.json({success: true}));
+    };
+    const composer = createAttachmentComposer({onChange() {}, onError: message => assert.fail(message)});
+    elements.imagePicker.files = [new File(["fixture"], "draft.png", {type: "image/png"})];
+    elements.imagePicker.onchange();
+    composer.saveDraft(1);
+    composer.restoreDraft(2);
+    assert.equal(composer.attachments.length, 0);
+    const metadata = {id: "12345678-1234-1234-1234-123456789abc"};
+    completeUpload(Response.json(metadata));
+    await new Promise(resolve => setTimeout(resolve, 0));
+    assert.deepEqual(deletes, []);
+    composer.saveDraft(2);
+    composer.restoreDraft(1);
+    assert.deepEqual(composer.attachments, [metadata]);
+    composer.discard();
+});