Draw the route-target highlight on the row's hover pill

The deep-link highlight swapped the row to a full-bleed band geometry
(negative margins, square corners, wider padding). That widened the text
column by ~8px, so long lines could rewrap and change the row's measured
height — in the virtualized timeline that makes Virtua re-measure and nudge
the scroll, once when the highlight appears and again when it clears.

Paint the tint on a before: pseudo sized to the row's own rounded-2xl hover
pill instead, so highlighted and idle rows are geometrically identical.
Share the class between MessageRow and the thread-summary wrapper so the
two can't drift again.

Signed-off-by: morgmart <98432065+morgmart@users.noreply.github.com>

desktop/src/features/messages/ui/MessageRow.tsx

@@ -55,6 +55,7 @@ import {
   MessageMetaSegments,
 } from "./MessageHeader";
 import { MessageTimestamp } from "./MessageTimestamp";
+import { ROUTE_TARGET_HIGHLIGHT_CLASS } from "./routeTargetHighlight";
 import { SentFromThreadLine } from "./SentFromThreadLine";
 import { WaveMessageAttachment } from "./WaveMessageAttachment";
 import { Tooltip, TooltipContent, TooltipTrigger } from "@/shared/ui/tooltip";
@@ -892,9 +893,7 @@ export const MessageRow = React.memo(
             "flex gap-2.5",
             isDisplayedAsContinuation ? "items-center" : "items-start",
             hasActiveReminder ? "bg-blue-500/10" : "",
-            highlighted
-              ? "-mx-4 rounded-none px-6 before:absolute before:-inset-y-1.5 before:inset-x-0 before:animate-[route-target-highlight-fade_2s_ease-out_forwards] before:bg-primary/10 before:content-[''] motion-reduce:before:animate-none sm:-mx-6 sm:px-8"
-              : "",
+            highlighted ? ROUTE_TARGET_HIGHLIGHT_CLASS : "",
           )}
           data-message-id={message.id}
           data-testid="message-row"

desktop/src/features/messages/ui/TimelineMessageRow.tsx

@@ -9,6 +9,7 @@ import type { UserProfileLookup } from "@/features/profile/lib/identity";
 import { cn } from "@/shared/lib/cn";
 import { MessageRow } from "./MessageRow";
 import { MessageThreadSummaryRow } from "./MessageThreadSummaryRow";
+import { ROUTE_TARGET_HIGHLIGHT_CLASS } from "./routeTargetHighlight";
 import { SystemMessageRow } from "./SystemMessageRow";
 
 type ToggleReaction = (
@@ -137,8 +138,7 @@ export function MessageRowItem({
       <div
         className={cn(
           "group/message relative mx-1 mb-1 flex flex-col gap-0 rounded-2xl px-0 py-1 transition-colors hover:bg-muted/50 focus-within:bg-muted/50",
-          isHighlighted &&
-            "-mx-4 px-4 before:absolute before:-inset-y-1.5 before:inset-x-0 before:animate-[route-target-highlight-fade_2s_ease-out_forwards] before:bg-primary/10 before:content-[''] motion-reduce:before:animate-none sm:-mx-6 sm:px-6",
+          isHighlighted && ROUTE_TARGET_HIGHLIGHT_CLASS,
         )}
       >
         <MessageRow

desktop/src/features/messages/ui/routeTargetHighlight.ts

@@ -0,0 +1,14 @@
+/**
+ * Classes that paint the "you were sent here" tint on a timeline row.
+ *
+ * The tint is drawn on a `before:` pseudo-element sized to the row's own
+ * hover pill (same `rounded-2xl` radius, no margin/padding change), so turning
+ * the highlight on or off never alters the row's geometry. In the virtualized
+ * timeline a geometry change would rewrap text, change the row's measured
+ * height, and make Virtua nudge the scroll position — once on arrival and
+ * again when the highlight clears.
+ *
+ * Hosts must be `relative` and use the `rounded-2xl` hover pill geometry.
+ */
+export const ROUTE_TARGET_HIGHLIGHT_CLASS =
+  "before:pointer-events-none before:absolute before:inset-0 before:rounded-2xl before:animate-[route-target-highlight-fade_2s_ease-out_forwards] before:bg-primary/10 before:content-[''] motion-reduce:before:animate-none";