[BUG] Dispatch on iOS Claude app stuck in 400 whitespace error loop — no self-service clear (continuation of #45217)

Summary

Dispatch (the mobile-to-PC task-bridge feature in the Claude iOS app) is stuck in a permanent 400 error loop. Every send to the Dispatch thread returns:

API Error: 400 — content contains white-space

The Dispatch thread cannot be cleared, deleted, or reset from any client-side UI (iOS app, claude.ai web, or reinstall). The conversation is server-side persistent, so users cannot recover from this state without Anthropic backend intervention.

Why this is filed as a separate issue from #41992

This was originally reported as #45217, which was auto-closed by the duplicate bot as a duplicate of #41992 and is now locked.

#41992 is about Claude Code CLI session JSONL corruption — the user-facing remediation path is to delete the local .jsonl session file. That works because CLI sessions are client-stored.

Dispatch is server-persisted, single-thread, no client-side state:

• There is no local file to delete.
• The iOS app has no "delete thread" / "clear history" / "new Dispatch" UI.
• claude.ai web has no Dispatch management UI.
• Reinstalling the iOS app does not reset state.

So while the underlying root cause may be shared (empty/whitespace content block in stored conversation history), the user-facing fix for #41992 does not solve Dispatch. This issue tracks the Dispatch-specific recoverability gap.

Steps to reproduce

Unclear what action put the Dispatch thread into this state — it occurred mid-session. Once in this state, it is fully reproducible:

1. Open Claude iOS app.
2. Send any message into the Dispatch thread.
3. Receive 400 content contains white-space.
4. Repeat indefinitely.

Expected behavior

Either:

• The whitespace-content block should not be persisted server-side in the first place (root-cause fix, shared with #41992), AND/OR
• The user should have a self-service way to clear or reset their Dispatch thread (e.g., a "Reset Dispatch" button in iOS settings or claude.ai).

Actual behavior

Permanent unrecoverable lock-out from the Dispatch feature without contacting Anthropic support.

Environment

• Claude iOS app (Dispatch feature)
• Account-level state (server-persisted)

References

• #45217 — original report, auto-closed and locked
• #41992 — listed duplicate parent (CLI session corruption; same root cause, different recoverability story)

Ask

1. Treat the Dispatch user-facing recoverability gap as in-scope (separate from the CLI fix in #41992).
2. Provide a self-service clear/reset mechanism for Dispatch.
3. In the meantime, document the support escalation path for affected users (current Anthropic support routes Dispatch tickets to the Connector/OAuth team, which doesn't address the issue).