refactor(app): share the compact time-ago prose formatter

Move the tab tooltip's "3m" -> "3m ago" wording into utils/time so the
usage card can reuse it.

packages/app/src/screens/workspace/workspace-desktop-tabs-row.tsx

@@ -69,6 +69,7 @@ import { RenderProfile } from "@/utils/render-profiler";
 import { TrailingActionScrim } from "@/components/ui/trailing-action-scrim";
 import { useKeyboardActionHandler } from "@/hooks/use-keyboard-action-handler";
 import { useCompactTimeAgo } from "@/hooks/use-compact-time-ago";
+import { formatCompactTimeAgoAsProse } from "@/utils/time";
 import { buildWorkspaceKeyboardHandlerId } from "@/keyboard/handler-id";
 import type { KeyboardActionDefinition } from "@/keyboard/keyboard-action-dispatcher";
 import { WorkspaceNewTabMenuContent } from "@/screens/workspace/workspace-new-tab-menu";
@@ -148,12 +149,6 @@ function formatAgentTooltipTitle(singleLineTitle: string): string {
   return `${singleLineTitle.slice(0, AGENT_TOOLTIP_TITLE_MAX_LENGTH - 1).trimEnd()}…`;
 }
 
-function formatAgentTooltipActivity(compactActivity: string): string {
-  if (compactActivity === "now") return "just now";
-  if (/^\d/.test(compactActivity)) return `${compactActivity} ago`;
-  return compactActivity;
-}
-
 function AgentTabTooltipBody({
   serverId,
   agentId,
@@ -169,7 +164,7 @@ function AgentTabTooltipBody({
     return state.agentLastActivity.get(agentId) ?? agent?.lastActivityAt ?? null;
   });
   const compactActivity = useCompactTimeAgo(lastActivityAt);
-  const activity = formatAgentTooltipActivity(compactActivity);
+  const activity = formatCompactTimeAgoAsProse(compactActivity);
 
   return (
     <View style={styles.tooltipAgentContent}>

packages/app/src/utils/time.test.ts

@@ -2,6 +2,7 @@ import { describe, it, expect } from "vitest";
 import {
   describeCompactTimeAgo,
   formatCompactTimeAgo,
+  formatCompactTimeAgoAsProse,
   formatDuration,
   formatMessageTimestamp,
   formatTimeAgo,
@@ -63,6 +64,15 @@ describe("describeCompactTimeAgo", () => {
   });
 });
 
+describe("formatCompactTimeAgoAsProse", () => {
+  it("puts elapsed labels back into prose and leaves dates alone", () => {
+    expect(formatCompactTimeAgoAsProse("now")).toBe("just now");
+    expect(formatCompactTimeAgoAsProse("3m")).toBe("3m ago");
+    expect(formatCompactTimeAgoAsProse("2h")).toBe("2h ago");
+    expect(formatCompactTimeAgoAsProse("Jan 15")).toBe("Jan 15");
+  });
+});
+
 describe("formatDuration", () => {
   it("renders sub-minute durations as whole seconds", () => {
     expect(formatDuration(0)).toBe("0s");

packages/app/src/utils/time.ts

@@ -91,6 +91,16 @@ export function formatCompactTimeAgo(date: Date, now: Date = new Date()): string
   return describeCompactTimeAgo(date, now).label;
 }
 
+/**
+ * A compact label put back into a sentence, for a tooltip or a line with room for prose:
+ * "now" → "just now", "5m" → "5m ago", "Jan 15" stays a date.
+ */
+export function formatCompactTimeAgoAsProse(label: string): string {
+  if (label === "now") return "just now";
+  if (/^\d/.test(label)) return `${label} ago`;
+  return label;
+}
+
 /**
  * How many local midnights lie between two instants: 0 for the same day, 1 for yesterday.
  * Counted on the calendar rather than in elapsed time, so six days and 23 hours ago on