Fix: always pull diagnostics on didOpen even if document is known via tab

When a document is restored from a tab (e.g., hot exit), the tab open
event fires before the didOpen notification. The tab handler triggers a
diagnostic pull with potentially stale content. Previously, when didOpen
fired, the knows() check would skip re-pulling diagnostics.

Now the didOpen handler always triggers a diagnostic pull. The existing
pullAsync logic handles deduplication - if a request is already active,
it cancels it and reschedules with the current document content.

Fixes #1558

Co-authored-by: dbaeumer <1931590+dbaeumer@users.noreply.github.com>

Author: Copilot

client/src/common/diagnostic.ts

@@ -864,10 +864,6 @@ class DiagnosticFeatureProviderImpl implements DiagnosticProviderShape {
 		const openFeature = client.getFeature(DidOpenTextDocumentNotification.method);
 		disposables.push(openFeature.onNotificationSent((event) => {
 			const textDocument = event.textDocument;
-			// We already know about this document. This can happen via a tab open.
-			if (this.diagnosticRequestor.knows(PullState.document, textDocument)) {
-				return;
-			}
 			if (matches(textDocument)) {
 				this.diagnosticRequestor.pull(textDocument, () => { addToBackgroundIfNeeded(textDocument); });
 			}