fix(site): stop hijacking navigation after archive-and-delete settles (#23372)

- Guard both `onSettled` callbacks in
`archiveAndDeleteMutation.mutate()` with `shouldNavigateAfterArchive()`,
which checks whether the user is still viewing the archived chat (or a
sub-agent of it) before calling `navigate("/agents")`
- Extract `shouldNavigateAfterArchive` into `agentWorkspaceUtils.ts`
with 6 unit test cases covering: direct match, different chat, no active
chat, sub-agent of archived parent, sub-agent of different parent, and
cache-cleared fallback
- Look up the active chat's `root_chat_id` from the per-chat query cache
(stable across WebSocket eviction of sub-agents) to handle the sub-agent
case

> 🤖 This PR was created with the help of Coder Agents, and has been
reviewed by my human. 🧑‍💻

site/src/pages/AgentsPage/AgentsPage.tsx

@@ -33,7 +33,10 @@ import { emptyInputStorageKey } from "./components/AgentCreateForm";
 import { maybePlayChime } from "./components/AgentDetail/useAgentChime";
 import { useAgentsPageKeybindings } from "./hooks/useAgentsPageKeybindings";
 import { useAgentsPWA } from "./hooks/useAgentsPWA";
-import { resolveArchiveAndDeleteAction } from "./utils/agentWorkspaceUtils";
+import {
+	resolveArchiveAndDeleteAction,
+	shouldNavigateAfterArchive,
+} from "./utils/agentWorkspaceUtils";
 import { getModelOptionsFromCatalog } from "./utils/modelOptions";
 import type { ChatDetailError } from "./utils/usageLimitMessage";
 
@@ -262,7 +265,27 @@ const AgentsPage: FC = () => {
 				archiveAndDeleteMutation.mutate(
 					{ chatId, workspaceId },
 					{
-						onSettled: () => navigate("/agents"),
+						onSettled: () => {
+							const activeChatId = activeChatIDRef.current;
+							if (
+								shouldNavigateAfterArchive(
+									activeChatId,
+									chatId,
+									// Read root_chat_id from the per-chat
+									// cache, which survives WebSocket eviction
+									// of sub-agents (only the parent's chatKey
+									// is removed). Must be read at settle time
+									// so it reflects the user's current location.
+									activeChatId
+										? queryClient.getQueryData<TypesGen.Chat>(
+												chatKey(activeChatId),
+											)?.root_chat_id
+										: undefined,
+								)
+							) {
+								navigate("/agents");
+							}
+						},
 					},
 				);
 			} else {
@@ -274,10 +297,23 @@ const AgentsPage: FC = () => {
 	};
 	const handleConfirmArchiveAndDelete = () => {
 		if (pendingArchiveAndDelete && !isArchiving) {
+			const { chatId: archivedChatId } = pendingArchiveAndDelete;
 			archiveAndDeleteMutation.mutate(pendingArchiveAndDelete, {
 				onSettled: () => {
 					setPendingArchiveAndDelete(null);
-					navigate("/agents");
+					const activeChatId = activeChatIDRef.current;
+					if (
+						shouldNavigateAfterArchive(
+							activeChatId,
+							archivedChatId,
+							activeChatId
+								? queryClient.getQueryData<TypesGen.Chat>(chatKey(activeChatId))
+										?.root_chat_id
+								: undefined,
+						)
+					) {
+						navigate("/agents");
+					}
 				},
 			});
 		}

site/src/pages/AgentsPage/utils/agentWorkspaceUtils.test.ts

@@ -2,6 +2,7 @@ import { describe, expect, it } from "vitest";
 import {
 	isWorkspaceAutoCreated,
 	resolveArchiveAndDeleteAction,
+	shouldNavigateAfterArchive,
 } from "./agentWorkspaceUtils";
 
 describe("isWorkspaceAutoCreated", () => {
@@ -80,3 +81,58 @@ describe("resolveArchiveAndDeleteAction", () => {
 		).rejects.toThrow("not found");
 	});
 });
+
+describe("shouldNavigateAfterArchive", () => {
+	it.each([
+		{
+			name: "user still viewing archived chat",
+			activeChatId: "abc-123",
+			archivedChatId: "abc-123",
+			expected: true,
+		},
+		{
+			name: "user navigated to a different chat",
+			activeChatId: "xyz-456",
+			archivedChatId: "abc-123",
+			expected: false,
+		},
+		{
+			name: "user navigated to /agents root (no active chat)",
+			activeChatId: undefined,
+			archivedChatId: "abc-123",
+			expected: false,
+		},
+		{
+			name: "user viewing sub-agent of archived parent",
+			activeChatId: "sub-agent-1",
+			archivedChatId: "parent-abc",
+			activeRootChatId: "parent-abc",
+			expected: true,
+		},
+		{
+			name: "user viewing sub-agent of a different parent",
+			activeChatId: "sub-agent-1",
+			archivedChatId: "parent-abc",
+			activeRootChatId: "parent-other",
+			expected: false,
+		},
+		{
+			name: "root chat ID not available (cache cleared)",
+			activeChatId: "sub-agent-1",
+			archivedChatId: "parent-abc",
+			activeRootChatId: undefined,
+			expected: false,
+		},
+	])(
+		"$name → $expected",
+		({ activeChatId, archivedChatId, activeRootChatId, expected }) => {
+			expect(
+				shouldNavigateAfterArchive(
+					activeChatId,
+					archivedChatId,
+					activeRootChatId,
+				),
+			).toBe(expected);
+		},
+	);
+});

site/src/pages/AgentsPage/utils/agentWorkspaceUtils.ts

@@ -12,6 +12,26 @@ export function isWorkspaceAutoCreated(
 	return new Date(workspaceCreatedAt) >= new Date(chatCreatedAt);
 }
 
+/**
+ * Returns whether the browser should navigate to /agents after an
+ * archive-and-delete mutation settles. Navigation is appropriate
+ * when the user is still viewing the archived chat or one of its
+ * sub-agents; if they already navigated elsewhere the redirect
+ * would be disruptive.
+ */
+export function shouldNavigateAfterArchive(
+	activeChatId: string | undefined,
+	archivedChatId: string,
+	activeRootChatId?: string,
+): boolean {
+	if (activeChatId === archivedChatId) return true;
+	// The active chat is a sub-agent rooted at the archived parent.
+	if (activeRootChatId != null && activeRootChatId === archivedChatId) {
+		return true;
+	}
+	return false;
+}
+
 /**
  * Resolves whether an archive-and-delete action should proceed
  * immediately or require user confirmation. Fetches the workspace