feat(tui): add width-budgeted "resumes when subagent finishes" status segment

When idle with a background subagent still in flight, append a tail status
segment spelling out that the agent resumes on its own. Width-budgeted like
every tail segment, so it drops first on a tight terminal where the ⛓ count
already carries the signal.

ui-tui/src/__tests__/appChromeStatusRule.test.tsx

@@ -129,6 +129,41 @@ describe('StatusRule background-subagent indicator', () => {
     expect(textContent(element)).not.toContain('⛓')
   })
 
+  it('spells out the auto-resume hint when idle with subagents in flight', () => {
+    const element = StatusRule({
+      ...baseProps,
+      usage: { ...baseProps.usage, active_subagents: 1 }
+    })
+
+    expect(textContent(element)).toContain('resumes when subagent finishes')
+  })
+
+  it('pluralizes the resume hint for multiple in-flight subagents', () => {
+    const element = StatusRule({
+      ...baseProps,
+      usage: { ...baseProps.usage, active_subagents: 3 }
+    })
+
+    expect(textContent(element)).toContain('resumes when 3 subagents finish')
+  })
+
+  it('hides the resume hint mid-turn (a busy turn owns the indicator)', () => {
+    const element = StatusRule({
+      ...baseProps,
+      busy: true,
+      turnStartedAt: Date.now(),
+      usage: { ...baseProps.usage, active_subagents: 2 }
+    })
+
+    expect(textContent(element)).not.toContain('resumes when')
+  })
+
+  it('omits the resume hint when no subagents are running', () => {
+    const element = StatusRule({ ...baseProps })
+
+    expect(textContent(element)).not.toContain('resumes when')
+  })
+
   it('drops the subagent segment before the bg segment on a narrow terminal', () => {
     // cols=44 is below the subagents breakpoint (92) but the bg breakpoint
     // (88) too — both gone. Assert the lower-priority subagent indicator is

ui-tui/src/components/appChrome.tsx

@@ -512,6 +512,15 @@ export function StatusRule({
   const showBg = segs.bg && bgCount > 0 && fits(SEP + stringWidth(`${bgCount} bg`))
   const subagentCount = typeof usage.active_subagents === 'number' ? usage.active_subagents : 0
   const showSubagents = segs.subagents && subagentCount > 0 && fits(SEP + stringWidth(`⛓ ${subagentCount}`))
+  // Parked-background reassurance: a top-level delegate_task runs in the
+  // background, so the turn ends (idle) while the subagent keeps working and its
+  // result re-enters as a fresh turn later. When idle with work still in flight,
+  // spell out that the agent resumes on its own — no spinner, nothing to poll.
+  // Width-budgeted like every tail segment, so it drops first on a tight
+  // terminal where ⛓ already carries the signal.
+  const resumeHintText =
+    subagentCount === 1 ? '↩ resumes when subagent finishes' : `↩ resumes when ${subagentCount} subagents finish`
+  const showResumeHint = !busy && subagentCount > 0 && fits(SEP + stringWidth(resumeHintText))
   // Dev-gated readout (HERMES_DEV_CREDITS), lowest priority,
   // so it consumes tail budget LAST and drops first on a narrow terminal.
   const showDevCredits = !!devCreditsText && fits(SEP + stringWidth(devCreditsText))
@@ -624,6 +633,12 @@ export function StatusRule({
             ⛓ {subagentCount}
           </Text>
         ) : null}
+        {showResumeHint ? (
+          <Text color={t.color.muted} dim wrap="truncate-end">
+            {' │ '}
+            {resumeHintText}
+          </Text>
+        ) : null}
         {showDevCredits ? (
           <Text color={t.color.accent} wrap="truncate-end">
             {' │ '}