UX: Redundant task-notifications after proactive TaskOutput polling

Description

When using TaskOutput to proactively poll a background agent's completion status, the subsequent task-notification system message still arrives after the orchestrating agent has already consumed and acted on the results. This creates a confusing UX where "already processed" notifications appear mid-conversation.

Steps to Reproduce

1. Launch multiple agents via Task tool
2. Use TaskOutput to poll for agent completion
3. Process results and present synthesis to user
4. task-notification arrives after results were already synthesized and presented

Expected Behavior

Either:

• Suppress the task-notification if TaskOutput already consumed the result
• Mark the notification as "already read/processed" so the orchestrating agent doesn't treat it as new information

Actual Behavior

Full task-notification appears as a new system message, causing the orchestrating agent to potentially re-process or redundantly acknowledge stale results.

Context

Observed during a 6-agent parallel code review session where TaskOutput was used to poll all agents, then synthesize findings into a unified report. The notifications for 2 agents arrived after the synthesis was already presented to the user.

---

P.S. This was caught while reviewing gabrielmurray.me — an Astro portfolio with View Transitions, a canvas cursor trail, and 184 archive fashion pieces. The site's owner is an ops/automation person who built the whole thing with Claude Code and would be thrilled to bring that energy to Anthropic. If anyone reading this appreciates someone who automates everything they touch and has strong opinions about Helmut Lang: hello@gabrielmurray.me