[BUG] Cowork Dispatch: visible output checker ignores SendUserMessage — infinite loop on macOS (post-update, July 2026)

What's Wrong

In Cowork Dispatch (macOS desktop app, latest version as of 2026-07-08), after every assistant turn the system injects:

[Your previous response had no visible output. Please continue and produce a user-visible response.]

This fires even when SendUserMessage returns "Message delivered to user" and the user can visibly see the response in the UI. The result is an infinite injection loop that cannot be broken from within the session. Persisted after updating Claude Desktop to the latest version and relaunching.

Relationship to Existing Issues

• #40142: same dispatch_agent_name: null → renderer TypeError → visible output checker misfires (Windows, March 2026). Fix either didn't ship or regressed.
• #44867: responses visible in background conversations but not main Dispatch thread.

What Should Happen

When SendUserMessage is called and returns "Message delivered to user", the visible output checker should not inject the loop trigger on the next turn.

Steps to Reproduce

1. Open Claude Desktop on macOS with Cowork enabled
2. Start a Dispatch conversation
3. Have assistant call SendUserMessage — confirm message is visible in UI
4. Observe: system injects [Your previous response had no visible output...] on next turn
5. Loop repeats indefinitely

Environment

• Platform: macOS, Claude Desktop (Cowork/Dispatch mode)
• Version: latest as of 2026-07-08
• Model: claude-sonnet-4-6