fix(app): make composer track clearance deterministic

Layout measurement excluded pill margin on some renderers, collapsing the intended gap above visible tracks. Keep the two-pill rail on one line and derive its complete tail clearance from shared geometry so chat switching and layout callbacks cannot change the result.

packages/app/src/agent-stream/bottom-overlay-inset.test.ts

@@ -5,8 +5,7 @@ describe("resolveBottomOverlayTailInset", () => {
   it("adds only the space missing after existing footer clearance", () => {
     expect(
       resolveBottomOverlayTailInset({
-        overlayHeight: 44,
-        clearance: 12,
+        requiredTailClearance: 56,
         existingTailSpacing: 24,
       }),
     ).toBe(32);
@@ -15,8 +14,7 @@ describe("resolveBottomOverlayTailInset", () => {
   it("reserves the full overlay and clearance when the tail has no spacing", () => {
     expect(
       resolveBottomOverlayTailInset({
-        overlayHeight: 44,
-        clearance: 12,
+        requiredTailClearance: 56,
         existingTailSpacing: 0,
       }),
     ).toBe(56);

packages/app/src/agent-stream/bottom-overlay-inset.ts

@@ -1,11 +1,9 @@
 export function resolveBottomOverlayTailInset({
-  overlayHeight,
-  clearance,
+  requiredTailClearance,
   existingTailSpacing,
 }: {
-  overlayHeight: number;
-  clearance: number;
+  requiredTailClearance: number;
   existingTailSpacing: number;
 }): number {
-  return Math.max(0, overlayHeight + clearance - existingTailSpacing);
+  return Math.max(0, requiredTailClearance - existingTailSpacing);
 }

packages/app/src/agent-stream/view.tsx

@@ -256,10 +256,8 @@ export interface AgentStreamViewProps {
   turnPresentation: TurnPresentation;
   routeBottomAnchorRequest?: BottomAnchorRouteRequest | null;
   isAuthoritativeHistoryReady?: boolean;
-  /** Measured transparent overlay at the bottom edge, rendered by the owning panel. */
-  bottomOverlayHeight?: number;
-  /** Visible space kept between the final content and that overlay. */
-  bottomOverlayClearance?: number;
+  /** Tail space required by a transparent overlay rendered at the bottom edge. */
+  bottomOverlayTailClearance?: number;
   toast?: ToastApi | null;
   onOpenWorkspaceFile?: (request: WorkspaceFileOpenRequest) => void;
   readOnly?: boolean;
@@ -308,8 +306,7 @@ const AgentStreamViewComponent = forwardRef<AgentStreamViewHandle, AgentStreamVi
       turnPresentation,
       routeBottomAnchorRequest = null,
       isAuthoritativeHistoryReady = true,
-      bottomOverlayHeight = 0,
-      bottomOverlayClearance = 0,
+      bottomOverlayTailClearance = 0,
       toast,
       onOpenWorkspaceFile,
       readOnly = false,
@@ -966,8 +963,7 @@ const AgentStreamViewComponent = forwardRef<AgentStreamViewHandle, AgentStreamVi
       const existingTailSpacing =
         auxiliary.turnFooter && !auxiliary.pendingPermissions ? TURN_FOOTER_BOTTOM_SPACING : 0;
       const bottomOverlayInset = resolveBottomOverlayTailInset({
-        overlayHeight: bottomOverlayHeight,
-        clearance: bottomOverlayClearance,
+        requiredTailClearance: bottomOverlayTailClearance,
         existingTailSpacing,
       });
       return renderLiveAuxiliaryNode({
@@ -975,12 +971,7 @@ const AgentStreamViewComponent = forwardRef<AgentStreamViewHandle, AgentStreamVi
         turnFooter: auxiliary.turnFooter,
         bottomOverlayInset,
       });
-    }, [
-      auxiliary.pendingPermissions,
-      auxiliary.turnFooter,
-      bottomOverlayClearance,
-      bottomOverlayHeight,
-    ]);
+    }, [auxiliary.pendingPermissions, auxiliary.turnFooter, bottomOverlayTailClearance]);
 
     const renderers = useMemo<StreamSegmentRenderers>(
       () => ({

packages/app/src/composer/pill-styles.ts

@@ -11,6 +11,11 @@ export function resolveComposerPillClearance(isCompact: boolean): number {
   return isCompact ? COMPOSER_PILL_CLEARANCE.compact : COMPOSER_PILL_CLEARANCE.wide;
 }
 
+export function resolveComposerTrackTailClearance(isCompact: boolean): number {
+  const clearance = resolveComposerPillClearance(isCompact);
+  return clearance + COMPOSER_PILL_MIN_HEIGHT + clearance;
+}
+
 /** Shared visual contract for the compact pills immediately above the composer. */
 export const composerPillStyles = StyleSheet.create((theme) => ({
   body: {

packages/app/src/composer/tracks.test.tsx

@@ -12,8 +12,18 @@ vi.mock("react-native", () => ({
   },
   Pressable: "button",
   Text: "span",
-  View: ({ children, style }: { children?: React.ReactNode; style?: unknown }) => (
-    <div data-style={JSON.stringify(style)}>{children}</div>
+  View: ({
+    children,
+    style,
+    onLayout,
+  }: {
+    children?: React.ReactNode;
+    style?: unknown;
+    onLayout?: unknown;
+  }) => (
+    <div data-style={JSON.stringify(style)} data-has-layout-handler={Boolean(onLayout)}>
+      {children}
+    </div>
   ),
 }));
 
@@ -53,6 +63,7 @@ import {
   COMPOSER_PILL_CLEARANCE,
   composerPillStyles,
   resolveComposerPillClearance,
+  resolveComposerTrackTailClearance,
 } from "./pill-styles";
 
 describe("ComposerTrackBar", () => {
@@ -89,8 +100,16 @@ describe("ComposerTrackBar", () => {
       right: 0,
       bottom: 0,
       paddingHorizontal: 16,
+      paddingBottom: { xs: 16, md: 10 },
     });
     expect(style).not.toHaveProperty("backgroundColor");
+    expect(container.firstElementChild?.getAttribute("data-has-layout-handler")).toBe("false");
+
+    const trackStyle = JSON.parse(
+      container.firstElementChild?.firstElementChild?.getAttribute("data-style") ?? "{}",
+    );
+    expect(trackStyle).toMatchObject({ flexDirection: "row" });
+    expect(trackStyle).not.toHaveProperty("flexWrap");
   });
 
   it("matches the composer's corner tangent without radius clamping", () => {
@@ -102,6 +121,8 @@ describe("ComposerTrackBar", () => {
     expect(composerPillStyles.label).toMatchObject({ fontSize: 12 });
     expect(resolveComposerPillClearance(true)).toBe(16);
     expect(resolveComposerPillClearance(false)).toBe(10);
+    expect(resolveComposerTrackTailClearance(true)).toBe(64);
+    expect(resolveComposerTrackTailClearance(false)).toBe(52);
     expect(COMPOSER_PILL_CLEARANCE).toEqual({ compact: 16, wide: 10 });
   });
 });

packages/app/src/composer/tracks.tsx

@@ -1,5 +1,5 @@
 import { useCallback, useMemo, useState, type ReactElement, type ReactNode } from "react";
-import { Pressable, Text, View, type LayoutChangeEvent } from "react-native";
+import { Pressable, Text, View } from "react-native";
 import { StyleSheet } from "react-native-unistyles";
 import {
   MenuRoot,
@@ -19,25 +19,16 @@ import { COMPOSER_PILL_CLEARANCE, composerPillStyles } from "./pill-styles";
  *
  * Everything in it is a pill: a count you can read without opening anything, and a panel behind
  * it for the detail. Trackers used to be stacked cards, so every one of them pushed the composer
- * further down the pane; a row of pills costs one line no matter how many there are.
+ * further down the pane. The bar has at most one subagent pill and one task pill, so it remains
+ * one line and has deterministic geometry on every platform.
  *
  * The bar floats over the transcript with no background, so content remains visible underneath.
  * Its host gives the scroll viewport a small bottom inset only when the bar exists; that keeps
  * the final footer clear without turning the overlay into a layout band.
  */
-export function ComposerTrackBar({
-  children,
-  onHeightChange,
-}: {
-  children: ReactNode;
-  onHeightChange?: (height: number) => void;
-}): ReactElement {
-  const handleLayout = useCallback(
-    (event: LayoutChangeEvent) => onHeightChange?.(event.nativeEvent.layout.height),
-    [onHeightChange],
-  );
+export function ComposerTrackBar({ children }: { children: ReactNode }): ReactElement {
   return (
-    <View style={styles.bar} pointerEvents="box-none" onLayout={handleLayout}>
+    <View style={styles.bar} pointerEvents="box-none">
       <View style={styles.track} pointerEvents="box-none">
         {children}
       </View>
@@ -126,7 +117,6 @@ function ComposerTrackPillTrigger({
   const pillStyle = useCallback(
     ({ hovered, pressed, open: isOpen }: MenuTriggerState) => [
       composerPillStyles.body,
-      styles.pillSpacing,
       (hovered || pressed || isOpen) && composerPillStyles.bodyActive,
     ],
     [],
@@ -246,21 +236,18 @@ const styles = StyleSheet.create((theme) => ({
     bottom: 0,
     alignItems: "center",
     paddingHorizontal: theme.spacing[4],
+    paddingBottom: {
+      xs: COMPOSER_PILL_CLEARANCE.compact,
+      md: COMPOSER_PILL_CLEARANCE.wide,
+    },
   },
   track: {
     width: "100%",
     maxWidth: MAX_CONTENT_WIDTH,
     flexDirection: "row",
-    flexWrap: "wrap",
     alignItems: "center",
     gap: theme.spacing[1],
   },
-  pillSpacing: {
-    marginBottom: {
-      xs: COMPOSER_PILL_CLEARANCE.compact,
-      md: COMPOSER_PILL_CLEARANCE.wide,
-    },
-  },
   // The rail every panel row sits on: inset from the panel edge so the fill is a rounded block
   // inside it, and tall enough that revealing an action button cannot resize the row.
   row: {

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

@@ -25,7 +25,7 @@ import { FileDropZone } from "@/components/file-drop/file-drop-zone";
 import { useRetainedPanelActive } from "@/components/retained-panel";
 import { SidebarCallout } from "@/components/sidebar-callout";
 import { Composer } from "@/composer";
-import { COMPOSER_PILL_MIN_HEIGHT, resolveComposerPillClearance } from "@/composer/pill-styles";
+import { resolveComposerTrackTailClearance } from "@/composer/pill-styles";
 import { getActiveMessageSubmissions } from "@/composer/submission/model";
 import { RewindComposerRestoreProvider } from "@/components/rewind/composer-restore";
 import { getProviderIcon } from "@/components/provider-icons";
@@ -1213,7 +1213,7 @@ const ChatAgentReadyContent = memo(function ChatAgentReadyContent({
 }) {
   const { t } = useTranslation();
   const isCompactFormFactor = useIsCompactFormFactor();
-  const composerPillClearance = resolveComposerPillClearance(isCompactFormFactor);
+  const composerTrackTailClearance = resolveComposerTrackTailClearance(isCompactFormFactor);
   const subagentRows = useSubagentsForParent({ serverId, parentAgentId: agentId });
   const tasks = useSessionStore((state): TodoEntry[] | undefined =>
     state.sessions[serverId]?.agentTasks.get(agentId),
@@ -1223,14 +1223,14 @@ const ChatAgentReadyContent = memo(function ChatAgentReadyContent({
     parentAgentId: agentId,
     rows: subagentRows,
   });
-  const showAgentTracks = hasAgentTracks({
-    subagentRows,
-    tasks,
-    archiveFinishedStatus: archiveFinishedSubagents.status,
-  });
-  const [agentTracksHeight, setAgentTracksHeight] = useState(
-    COMPOSER_PILL_MIN_HEIGHT + composerPillClearance,
-  );
+  const hasActiveComposer = !agentState.archivedAt && !isArchivingCurrentAgent;
+  const showAgentTracks =
+    hasActiveComposer &&
+    hasAgentTracks({
+      subagentRows,
+      tasks,
+      archiveFinishedStatus: archiveFinishedSubagents.status,
+    });
   const rawAgentInputDraft = useAgentInputDraft({
     draftKey: buildDraftStoreKey({
       serverId,
@@ -1305,8 +1305,7 @@ const ChatAgentReadyContent = memo(function ChatAgentReadyContent({
           agent={effectiveAgent}
           routeBottomAnchorRequest={routeBottomAnchorRequest}
           hasAppliedAuthoritativeHistory={hasAppliedAuthoritativeHistory}
-          bottomOverlayHeight={showAgentTracks ? agentTracksHeight : 0}
-          bottomOverlayClearance={showAgentTracks ? composerPillClearance : 0}
+          bottomOverlayTailClearance={showAgentTracks ? composerTrackTailClearance : 0}
           toast={toastApi}
           onOpenWorkspaceFile={onOpenWorkspaceFile}
         />
@@ -1318,7 +1317,6 @@ const ChatAgentReadyContent = memo(function ChatAgentReadyContent({
           tasks={tasks}
           archiveFinishedStatus={archiveFinishedSubagents.status}
           onArchiveFinished={archiveFinishedSubagents.archiveFinished}
-          onHeightChange={setAgentTracksHeight}
         />
       ) : null}
     </ReanimatedAnimated.View>
@@ -1372,8 +1370,7 @@ const AgentStreamSection = memo(function AgentStreamSection({
   agent,
   routeBottomAnchorRequest,
   hasAppliedAuthoritativeHistory,
-  bottomOverlayHeight,
-  bottomOverlayClearance,
+  bottomOverlayTailClearance,
   toast,
   onOpenWorkspaceFile,
 }: {
@@ -1383,8 +1380,7 @@ const AgentStreamSection = memo(function AgentStreamSection({
   agent: AgentScreenAgent;
   routeBottomAnchorRequest: RouteBottomAnchorRequest;
   hasAppliedAuthoritativeHistory: boolean;
-  bottomOverlayHeight: number;
-  bottomOverlayClearance: number;
+  bottomOverlayTailClearance: number;
   toast: ReturnType<typeof useToastHost>["api"];
   onOpenWorkspaceFile?: (request: WorkspaceFileOpenRequest) => void;
 }) {
@@ -1443,8 +1439,7 @@ const AgentStreamSection = memo(function AgentStreamSection({
       pendingPermissions={pendingPermissions}
       routeBottomAnchorRequest={routeBottomAnchorRequest}
       isAuthoritativeHistoryReady={hasAppliedAuthoritativeHistory}
-      bottomOverlayHeight={bottomOverlayHeight}
-      bottomOverlayClearance={bottomOverlayClearance}
+      bottomOverlayTailClearance={bottomOverlayTailClearance}
       toast={toast}
       pendingMessageSubmissions={pendingMessageSubmissions}
       turnPresentation={turnPresentation}

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

@@ -26,14 +26,12 @@ export const AgentTracks = memo(function AgentTracks({
   tasks,
   archiveFinishedStatus,
   onArchiveFinished,
-  onHeightChange,
 }: {
   serverId: string;
   subagentRows: SubagentRow[];
   tasks: TodoEntry[] | undefined;
   archiveFinishedStatus: ArchiveFinishedStatus;
   onArchiveFinished: () => void;
-  onHeightChange?: (height: number) => void;
 }): ReactElement | null {
   const { openTab } = usePaneContext();
   const canDetachSubagents = useSessionStore(
@@ -59,7 +57,7 @@ export const AgentTracks = memo(function AgentTracks({
   }
 
   return (
-    <ComposerTrackBar onHeightChange={onHeightChange}>
+    <ComposerTrackBar>
       <SubagentsTrack
         rows={subagentRows}
         onOpenSubagent={handleOpenSubagent}