[luv-292] fix: keep virtualizer scrollMargin in sync with layout shifts

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## Unreleased
 
 ### Fixes
+- Session log viewer: stop rendering log entries at the wrong y-offset (which exposed the page background and looked like the page "going blue" while scrolling). `app/components/raw-log-viewer.tsx` was capturing the virtualizer's `scrollMargin` once via a callback ref on the list wrapper's `offsetTop`. That ref fires only on mount, so any layout shift above the list — most commonly the async `searchHookActivityAction` resolving and mounting the `<SessionHooksPanel>` panel above the Logs section, but also Subagents-section / per-subagent collapse-expand, and window resizes that re-flow the StatsBar / ToolStatsGrid — left `scrollMargin` stale. The `useWindowVirtualizer` then computed the wrong visible window in list-local coordinates and positioned each item at `transform: translateY(virtualRow.start - staleScrollMargin)`, so items appeared shifted by the layout-delta (typically tens to hundreds of pixels). Replace the callback ref with a stable `useRef<HTMLDivElement>` and a `useLayoutEffect` that reads `getBoundingClientRect().top + window.scrollY` (more robust than `offsetTop` against future positioned ancestors) and re-reads it from a `ResizeObserver` watching `document.body` plus a `window` resize listener. Functional `setScrollMargin(prev => prev === top ? prev : top)` short-circuits same-value updates so the body-resize that the state-update itself causes can't loop. (#292)
 - Detect when `failproofai` on the user's PATH is shadowed by a different, older install (classic cause: a leftover `bun link` from a prior dev session, or a previously-installed `bun install -g failproofai` whose `~/.bun/bin` prefix sorts ahead of npm's). New `scripts/install-diagnosis.mjs` helper resolves the PATH-first install via `command -v` (POSIX) / `where` (Win32), compares its package root + version against the running install, and surfaces a copy-pasteable cleanup command (`rm -f ~/.bun/bin/failproofai && rm -rf ~/.bun/install/global/node_modules/failproofai` for bun-side shadows, `npm rm -g failproofai` for npm-side ones). Wired into two places: (1) `scripts/postinstall.mjs` warns at install time when the just-installed copy is being shadowed, before the customer ever sees the runtime error, (2) `scripts/launch.ts` rewrites the existing "Cannot find server.js at" error to point at the actual stale install (with both versions and the cleanup command) when the missing build output is caused by a PATH shadow rather than a genuinely broken build. Replaces the previous misleading recommendation (`npm install -g failproofai@latest`) which doesn't help when the new install is itself being shadowed (#286).
 
 ## 0.0.10-beta.0 — 2026-05-04

app/components/raw-log-viewer.tsx

@@ -5,7 +5,7 @@
  */
 "use client";
 
-import React, { useCallback, useEffect, useMemo, useRef, useState } from "react";
+import React, { useCallback, useEffect, useLayoutEffect, useMemo, useRef, useState } from "react";
 import { useWindowVirtualizer } from "@tanstack/react-virtual";
 import { ChevronDown, Wrench } from "lucide-react";
 import type { LogEntry, ToolUseBlock } from "@/lib/log-entries";
@@ -209,9 +209,29 @@ function VirtualizedEntryList({ entries, entriesBySource, projectName, sessionId
   const [highlightedUuid, setHighlightedUuid] = useState<string | null>(() => parseHashUuid());
   const highlightTimerRef = useRef<ReturnType<typeof setTimeout>>(undefined);
   const hasScrolledRef = useRef(false);
-
-  const listCallbackRef = useCallback((node: HTMLDivElement | null) => {
-    if (node) setScrollMargin(node.offsetTop);
+  const listRef = useRef<HTMLDivElement>(null);
+
+  // Keep `scrollMargin` in sync with the list's actual document offset.
+  // A one-shot callback ref would go stale whenever something above the list
+  // shifts (async hook-activity panel mounting, subagent collapse/expand,
+  // window resize) — leaving the virtualizer to render items at the wrong
+  // y-offset and exposing the page background under the (otherwise empty)
+  // virtualized container.
+  useLayoutEffect(() => {
+    const el = listRef.current;
+    if (!el) return;
+    const update = () => {
+      const top = el.getBoundingClientRect().top + window.scrollY;
+      setScrollMargin((prev) => (prev === top ? prev : top));
+    };
+    update();
+    const ro = new ResizeObserver(update);
+    ro.observe(document.body);
+    window.addEventListener("resize", update);
+    return () => {
+      ro.disconnect();
+      window.removeEventListener("resize", update);
+    };
   }, []);
 
   const segments = useMemo(() => computeSegments(entries), [entries]);
@@ -337,7 +357,7 @@ function VirtualizedEntryList({ entries, entriesBySource, projectName, sessionId
   }, [highlightedUuid, parentUuidForSubagent, uuidToIndex, virtualizer]);
 
   return (
-    <div ref={listCallbackRef}>
+    <div ref={listRef}>
       <div
         style={{
           height: `${virtualizer.getTotalSize()}px`,