swarm ui: say what a subagent's age counts from, and the list's two lookup passes

A running status shows 'running since', a stale one shows no age, since its
time is when the run began. The reference now says the status reads and the row
lookups are two passes, so the list waits up to four seconds in all.

frontend/packages/swarm-ui/src/agent/terminal/SubagentTerms.tsx

@@ -15,7 +15,7 @@ import { Badge } from "@hive/shared/badge.js";
 import { AgentTermPreview } from "./AgentTermPreview.js";
 import {
   isDimmed,
-  lastActive,
+  ageUnix,
   runLabel,
   stateLabel,
   stillListed,
@@ -51,7 +51,7 @@ export function SubagentTerms({ agentName }: { agentName: string }) {
         {subagents?.map((sub) => {
           const { name } = sub;
           const runs = runLabel(sub);
-          const active = lastActive(sub);
+          const active = ageUnix(sub);
           const status = stateLabel(sub);
           const stale = isDimmed(sub, nowS);
           return (

frontend/packages/swarm-ui/src/agent/terminal/SubagentsMenu.tsx

@@ -22,7 +22,7 @@ import { Popover } from "../../ui/popover/Popover.js";
 import { RelativeTime } from "../../ui/relative-time/RelativeTime.js";
 import { termPaths } from "./term-paths.js";
 import {
-  lastActive,
+  ageUnix,
   runLabel,
   runningLabel,
   splitRunning,
@@ -56,9 +56,9 @@ function Entry({
       {stateLabel(sub) && (
         <span class="ui-subagents-menu-age">{stateLabel(sub)}</span>
       )}
-      {lastActive(sub) !== null && (
+      {ageUnix(sub) !== null && (
         <span class="ui-subagents-menu-age">
-          <RelativeTime epochMs={(lastActive(sub) ?? 0) * 1000} />
+          <RelativeTime epochMs={(ageUnix(sub) ?? 0) * 1000} />
         </span>
       )}
     </>

frontend/packages/swarm-ui/src/agent/terminal/subagent-list.ts

@@ -68,12 +68,15 @@ export function isDimmed(sub: Subagent, nowS: number): boolean {
 }
 
 /**
- * A word for a state that is neither running nor unknown, to show beside the
- * subagent: `finished`, or `stopped reporting` for a stale status. Empty
- * when running or when the daemon published no status.
+ * The word shown before a subagent's age, which says what the age counts from:
+ * `running since` for a running status, `finished` for a finished one,
+ * `stopped reporting` for a stale one. Empty when the daemon published no
+ * status, where the age is the newest row's.
  */
 export function stateLabel(sub: Subagent): string {
   switch (sub.state ?? null) {
+    case "running":
+      return "running since";
     case "finished":
       return "finished";
     case "stale":
@@ -83,6 +86,15 @@ export function stateLabel(sub: Subagent): string {
   }
 }
 
+/**
+ * The time to show as an age, unix seconds, or `null` for none. A stale
+ * status has none: its time is when the run began, which would read as when
+ * the daemon stopped reporting.
+ */
+export function ageUnix(sub: Subagent): number | null {
+  return (sub.state ?? null) === "stale" ? null : lastActive(sub);
+}
+
 /** Newest first; a subagent whose time could not be read sorts last. */
 export function byRecency(a: Subagent, b: Subagent): number {
   const ta = lastActive(a) ?? -Infinity;

frontend/packages/swarm-ui/test/subagent-list.test.mjs

@@ -5,6 +5,7 @@ import assert from "node:assert/strict";
 import { test } from "node:test";
 import {
   STALE_S,
+  ageUnix,
   byRecency,
   isDimmed,
   isRunning,
@@ -99,13 +100,20 @@ test("only a subagent without a status falls back to the row's age", () => {
   assert.equal(isDimmed(withState("a", "stale", 5), NOW), true);
 });
 
-test("the state word names finished and stale subagents only", () => {
+test("the state word says what the age counts from", () => {
   assert.equal(stateLabel(withState("a", "finished", 5)), "finished");
   assert.equal(stateLabel(withState("a", "stale", 5)), "stopped reporting");
-  assert.equal(stateLabel(withState("a", "running", 5)), "");
+  assert.equal(stateLabel(withState("a", "running", 5)), "running since");
   assert.equal(stateLabel(sub("a", 5)), "");
 });
 
+test("a stale status shows no age, the others show theirs", () => {
+  assert.equal(ageUnix(withState("a", "stale", 500)), null);
+  assert.equal(ageUnix(withState("a", "running", 500)), NOW - 500);
+  assert.equal(ageUnix(withState("a", "finished", 500)), NOW - 500);
+  assert.equal(ageUnix(sub("a", 30)), NOW - 30);
+});
+
 test("a subagent with only a status sorts by when its state began", () => {
   const list = [
     withState("old", "finished", 500),