The composer completes mentions and hashtags

A mention or hashtag being written at the end of the words is offered, once typing pauses, the accounts or tags
PrivaPub already knows (/api/v2/search, never resolving); a click writes it out. e2e: a town persona's handle,
begun, is offered and completed. CLAUDE.md also says that FEP-5624's moderated comments (PeerTube) show as pending
on a card, as GoToSocial's policies do.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

tests/e2e/Actions/ComposerTests.cs

@@ -59,6 +59,29 @@ namespace decePubClient.E2E.Actions
 			}
 		}
 
+		// a mention being written is offered the accounts PrivaPub knows, and a click writes the whole handle out
+		[Fact]
+		public async Task A_mention_being_written_is_completed_from_the_accounts_the_server_knows()
+		{
+			var personas = Pasture.Personas();
+			Assert.SkipWhen(personas.Count < 2, "the town has one persona");
+			var (author, other) = (personas[0], personas[1]);
+			var acct = (await PersonaApi.Call(other, "/api/v1/accounts/verify_credentials"))!["acct"]!.GetValue<string>();
+			await using var session = await SignIn.As(browser, author);
+			var page = session.Page;
+			await Results.Cell("client.action.mention-suggestion", "privapub", author.UserName, async () =>
+			{
+				await OpenHome(page);
+				await page.GetByRole(AriaRole.Button, new() { Name = "Post" }).First.ClickAsync();
+				var box = page.Locator("textarea[data-compose]").First;
+				await box.FillAsync("hello @" + acct[..Math.Min(4, acct.Length)]);
+				await page.Locator($"[data-suggestions] [data-suggestion='@{acct}']").ClickAsync(new() { Timeout = 15000 });
+				await Assertions.Expect(box).ToHaveValueAsync($"hello @{acct} ");
+				await Assertions.Expect(page.Locator("[data-suggestions]")).ToHaveCountAsync(0);
+				await session.AssertGuards();
+			}, page);
+		}
+
 		[Fact]
 		public async Task The_personas_own_post_is_edited_and_quoted_from_its_card()
 		{