fix(app): float composer track pills consistently

Keep agent and task pills as a transparent transcript overlay while measuring their rendered height for scroll-tail clearance. Share geometry and spacing with the import-session pill so borders, type, corners, and composer separation match across platforms.

packages/app/src/panels/agent-tracks.tsx

@@ -4,46 +4,43 @@ import { ComposerTrackBar } from "@/composer/tracks";
 import { usePaneContext } from "@/panels/pane-context";
 import { useSessionStore } from "@/stores/session-store";
 import {
-  useArchiveFinishedSubagents,
+  type ArchiveFinishedStatus,
   useArchiveSubagent,
   useDetachSubagent,
-  useSubagentsForParent,
+  type SubagentRow,
 } from "@/subagents";
 import { SubagentsTrack } from "@/subagents/track";
+import type { TodoEntry } from "@/types/stream";
 import { navigateToAgent } from "@/utils/navigate-to-agent";
 
 /**
- * The pane's trackers — its subagents and its task list — as a row of pills over the foot of
- * the transcript.
+ * The pane's trackers — its subagents and its task list — as a row of pills above the composer.
  *
- * It is mounted inside the transcript's animated container rather than above the composer, and
- * that placement is the whole design: the pills paint over the timeline, so scrolled content
- * passes under them instead of stopping at a band, and the container carries the same keyboard
- * transform the composer does, so the pills stay glued to its top edge while the keyboard moves.
- *
- * Its state was living in the composer only because that is where it used to render. None of it
- * is composer state — a subagent row opens a tab, the task list reads the agent's stream.
+ * The row shares the composer's keyboard transform and owns the space between itself and the
+ * transcript. Its data remains agent state: a subagent row opens a tab and the task list reads
+ * the agent's stream.
  */
 export const AgentTracks = memo(function AgentTracks({
   serverId,
-  agentId,
+  subagentRows,
+  tasks,
+  archiveFinishedStatus,
+  onArchiveFinished,
+  onHeightChange,
 }: {
   serverId: string;
-  agentId: string;
-}): ReactElement {
+  subagentRows: SubagentRow[];
+  tasks: TodoEntry[] | undefined;
+  archiveFinishedStatus: ArchiveFinishedStatus;
+  onArchiveFinished: () => void;
+  onHeightChange?: (height: number) => void;
+}): ReactElement | null {
   const { openTab } = usePaneContext();
-  const subagentRows = useSubagentsForParent({ serverId, parentAgentId: agentId });
   const canDetachSubagents = useSessionStore(
     (state) => state.sessions[serverId]?.serverInfo?.features?.agentDetach === true,
   );
   const archiveSubagent = useArchiveSubagent({ serverId });
   const detachSubagent = useDetachSubagent({ serverId });
-  const archiveFinishedSubagents = useArchiveFinishedSubagents({
-    serverId,
-    parentAgentId: agentId,
-    rows: subagentRows,
-  });
-
   const handleOpenSubagent = useCallback(
     (subagentId: string) => {
       navigateToAgent({ serverId, agentId: subagentId });
@@ -57,18 +54,34 @@ export const AgentTracks = memo(function AgentTracks({
     [openTab],
   );
 
+  if (!hasAgentTracks({ subagentRows, tasks, archiveFinishedStatus })) {
+    return null;
+  }
+
   return (
-    <ComposerTrackBar>
+    <ComposerTrackBar onHeightChange={onHeightChange}>
       <SubagentsTrack
         rows={subagentRows}
         onOpenSubagent={handleOpenSubagent}
         onOpenProviderSubagent={handleOpenProviderSubagent}
         onArchiveSubagent={archiveSubagent}
-        onArchiveFinished={archiveFinishedSubagents.archiveFinished}
-        archiveFinishedStatus={archiveFinishedSubagents.status}
+        onArchiveFinished={onArchiveFinished}
+        archiveFinishedStatus={archiveFinishedStatus}
         onDetachSubagent={canDetachSubagents ? detachSubagent : undefined}
       />
-      <AgentTaskList serverId={serverId} agentId={agentId} />
+      <AgentTaskList tasks={tasks} />
     </ComposerTrackBar>
   );
 });
+
+export function hasAgentTracks({
+  subagentRows,
+  tasks,
+  archiveFinishedStatus,
+}: {
+  subagentRows: readonly SubagentRow[];
+  tasks: readonly TodoEntry[] | undefined;
+  archiveFinishedStatus: ArchiveFinishedStatus;
+}): boolean {
+  return subagentRows.length > 0 || Boolean(tasks?.length) || archiveFinishedStatus.kind !== "idle";
+}