fix(desktop): anchor activity message hover cues

Co-authored-by: Rizz <302abe414ca6e3134763d2539bfcf145aea2a63fe5f8455204ed602fd40cf381@buzz.block.builderlab.xyz>
Signed-off-by: Rizz <302abe414ca6e3134763d2539bfcf145aea2a63fe5f8455204ed602fd40cf381@buzz.block.builderlab.xyz>

desktop/src/features/agents/ui/AgentSessionToolItem/CompactMessageSummary.tsx

@@ -151,6 +151,7 @@ export function CompactMessageSummary({
                 ? "text-xs leading-4"
                 : "text-sm leading-relaxed",
               shouldClampBubble && "relative max-h-36 overflow-hidden",
+              isConversation && "relative",
               canOpenMessage &&
                 "group/bubble cursor-pointer transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring",
               isCompactPreview

desktop/src/features/agents/ui/AgentSessionTranscriptList.conversation.test.mjs

@@ -64,7 +64,20 @@ test("conversation renders the prompt as a filled right-aligned bubble with an a
   // soft tint, borderless surface, and `px-4 py-2` spacing.
   const bubble = row.querySelector(".rounded-2xl");
   assert.ok(bubble, "the prompt should match Buzz's chat-bubble radius");
+  assert.match(bubble.className, /relative/);
   assert.match(bubble.className, /bg-muted\/60/);
+  const openInChatCue = bubble.querySelector('[aria-hidden="true"]');
+  assert.ok(openInChatCue, "linked prompts should retain the hover cue");
+  assert.match(
+    openInChatCue.className,
+    /top-1\.5/,
+    "the sender hover cue uses its native inset once the bubble is its containing block",
+  );
+  assert.doesNotMatch(
+    openInChatCue.className,
+    /top-3/,
+    "the cue should not be pushed into the prompt text to compensate for the old containing-block bug",
+  );
   assert.doesNotMatch(
     bubble.className,
     /(?<!\/)bg-muted(?!\/)/,

desktop/src/features/agents/ui/AgentSessionWorkBlock.orphaned.test.mjs

@@ -398,6 +398,7 @@ test("the same relay post outside a work block keeps its message bubble", async
     bubble,
     "outside a block a posted message is a destination the reader can open — the bubble stays",
   );
+  assert.match(bubble.className, /relative/);
   assert.doesNotMatch(
     bubble.className,
     /max-h-36/,

desktop/src/features/agents/ui/activityRenderClasses/UserMessageBubble.tsx

@@ -185,7 +185,7 @@ export function UserMessageBubble({
             // `leading-normal` overrides the `leading-relaxed` base, as berd
             // does, so the prompt sits tighter than the agent's prose.
             isConversation &&
-              "rounded-2xl border-0 bg-muted/60 px-4 py-2 leading-normal",
+              "relative rounded-2xl border-0 bg-muted/60 px-4 py-2 leading-normal",
             bubbleClassName,
           )}
           ref={bubbleRef}
@@ -206,11 +206,7 @@ export function UserMessageBubble({
           {hasBubbleOverflow ? (
             <span className="pointer-events-none absolute inset-x-0 bottom-0 h-8 rounded-b-2xl bg-linear-to-b from-transparent to-background" />
           ) : null}
-          {messageLink ? (
-            <MessageLinkHoverCue
-              className={isConversation ? "top-3" : undefined}
-            />
-          ) : null}
+          {messageLink ? <MessageLinkHoverCue /> : null}
         </div>
         {isConversation && footer ? (
           // Timestamp/context row is chrome, not content: focus mode keeps it