fix(pi): name workflow child rows by their step key, not only the agent (#26909)

pi-subagents never sends a description, so every child row fell back to
the agent name and two children on one agent read the same. Workflow
children do carry workflowKey, a bounded slug, so use it as the label.

Fixes #26908

src/main/pi/agent-status-extension-async-subagents.test.ts

@@ -180,6 +180,40 @@ describe('Pi child rows', () => {
     ])
   })
 
+  it('names workflow children that share an agent by their workflow step key', async () => {
+    const harness = createAgentStatusExtensionHarness({ kind: 'pi' })
+    startWorkflow(harness)
+    // pi-subagents 0.76.1 tags each scripted-workflow child with the key it was launched under.
+    for (const key of ['review-code', 'review-rollout']) {
+      harness.emitPiEvent('subagent:async-started', {
+        id: `run-${key}`,
+        mode: 'single',
+        agent: 'reviewer',
+        pid: 4000,
+        parentWorkflowRunId: WORKFLOW,
+        workflowKey: key
+      })
+    }
+    await vi.advanceTimersByTimeAsync(0)
+
+    expect(posts(harness).at(-1)?.subagents).toEqual([
+      {
+        id: 'run-review-code',
+        state: 'working',
+        startedAt: expect.any(Number),
+        agentType: 'reviewer',
+        description: 'review-code'
+      },
+      {
+        id: 'run-review-rollout',
+        state: 'working',
+        startedAt: expect.any(Number),
+        agentType: 'reviewer',
+        description: 'review-rollout'
+      }
+    ])
+  })
+
   it('posts an OMP task child with its description', async () => {
     const harness = createAgentStatusExtensionHarness({ kind: 'omp' })
     await harness.callHook('session_start')

src/main/pi/agent-status-subagent-roster-source.ts

@@ -107,15 +107,16 @@ export function getPiSubagentRosterEventSourceLines(): string[] {
     "  const readLabel = (value: unknown): string | undefined => typeof value === 'string' && value.trim() ? value : undefined",
     '  lifecycleState.onEvent = (event: unknown, forcedStatus?: string): void => {',
     "    if (!event || typeof event !== 'object') return",
-    '    const record = event as { id?: unknown; runId?: unknown; agent?: unknown; description?: unknown; mode?: unknown; parentWorkflowRunId?: unknown }',
+    '    const record = event as { id?: unknown; runId?: unknown; agent?: unknown; description?: unknown; workflowKey?: unknown; mode?: unknown; parentWorkflowRunId?: unknown }',
     "    const id = typeof record.id === 'string' && record.id ? record.id : typeof record.runId === 'string' ? record.runId : ''",
     '    const status = forcedStatus ?? (event as { status?: unknown }).status',
     '    if (!id) return',
     '    if (isOmpRuntime() && !lifecycleState.ownsPane) return',
     "    if (status === 'started') {",
     '      lifecycleState.active.add(id)',
-    // Why: pi-subagents redacts task prompts, so only the agent name and OMP's short label are shown.
-    "      if (!subagentDetails.has(id)) subagentDetails.set(id, { agentType: readLabel(record.agent), description: readLabel(record.description), startedAt: Date.now(), workflow: record.mode === 'workflow', parent: readLabel(record.parentWorkflowRunId), registration })",
+    // Why: pi-subagents redacts task prompts, so only the agent name, OMP's short label and a
+    // workflow child's step key are shown. The key tells apart siblings that share an agent.
+    "      if (!subagentDetails.has(id)) subagentDetails.set(id, { agentType: readLabel(record.agent), description: readLabel(record.description) ?? readLabel(record.workflowKey), startedAt: Date.now(), workflow: record.mode === 'workflow', parent: readLabel(record.parentWorkflowRunId), registration })",
     // Why: Pi re-opens only a posted completion; an earlier child must leave the idle check intact.
     '      if (!isTurnInFlight() && (isOmpRuntime() || lifecycleState.runGeneration === 0 || lifecycleState.completionPostedGeneration === lifecycleState.runGeneration)) {',
     '        lifecycleState.waiting = true',