feat(web): scroll to file when clicking prologue focus area links

Add scrollTo search param to the Files route. When a focus area's
file link is clicked, it navigates to Files changed and scrolls to
that specific file, matching the hosted Stage monorepo's behavior.

Author: dastratakos

packages/web/src/app/runs.$runId.files.tsx

@@ -1,11 +1,18 @@
 import { createFileRoute } from "@tanstack/react-router";
+import { z } from "zod";
 import { FilesPage } from "@/routes/files-page";
 
+const filesSearchSchema = z.object({
+	scrollTo: z.string().optional(),
+});
+
 export const Route = createFileRoute("/runs/$runId/files")({
+	validateSearch: (search) => filesSearchSchema.parse(search),
 	component: FilesRoute,
 });
 
 function FilesRoute() {
 	const { runId } = Route.useParams();
-	return <FilesPage runId={runId} />;
+	const { scrollTo } = Route.useSearch();
+	return <FilesPage runId={runId} scrollTo={scrollTo} />;
 }

packages/web/src/components/prologue/prologue-section.tsx

@@ -84,6 +84,7 @@ function PrologueDisplay({ prologue, runId }: { prologue: Prologue; runId: strin
 										<Link
 											to="/runs/$runId/files"
 											params={{ runId }}
+											search={{ scrollTo: area.locations[0] }}
 											className="ml-auto shrink-0 text-xs text-muted-foreground transition-colors hover:text-foreground"
 										>
 											{getFileName(area.locations[0])} &rarr;

packages/web/src/routes/files-page.tsx

@@ -1,4 +1,4 @@
-import { useCallback, useMemo, useRef, useState } from "react";
+import { useCallback, useEffect, useMemo, useRef, useState } from "react";
 import { useHotkeys } from "react-hotkeys-hook";
 import {
 	FileDiffList,
@@ -19,9 +19,10 @@ import { useViewState } from "@/lib/use-view-state";
 
 interface FilesPageProps {
 	runId: string;
+	scrollTo?: string;
 }
 
-export function FilesPage({ runId }: FilesPageProps) {
+export function FilesPage({ runId, scrollTo }: FilesPageProps) {
 	const { data, isLoading, error } = useDiffPatch(runId);
 
 	const rawEntries = useFileDiffEntries(data);
@@ -62,6 +63,12 @@ export function FilesPage({ runId }: FilesPageProps) {
 		[setActiveFileManually],
 	);
 
+	useEffect(() => {
+		if (scrollTo && !isLoading) {
+			diffListRef.current?.scrollToFile(scrollTo);
+		}
+	}, [scrollTo, isLoading]);
+
 	const [isPickerCollapsed, setIsPickerCollapsed] = useState(false);
 	useHotkeys(KEYBOARD_SHORTCUTS.TOGGLE_FILES.hotkey, () => setIsPickerCollapsed((c) => !c), {
 		preventDefault: true,