Mobile app: '+' create-session flow fails with 'The request was invalid' on every environment; web works

Summary

The "+" (new session) flow in the Claude Code iOS mobile app fails with "Failed to send message — The request was invalid" on the first message of every newly created session. The web app (claude.ai/code) does not exhibit the bug — same account, same environments, "+" create flow works fine.

Repro

1. iOS app, tap "+" in the sidebar to create a new session.
2. Select any environment (reproduced on multiple — cc-rh-austin:renfroe-holdings, others).
3. Mode picker says "Code".
4. Type any message (e.g. Testing).
5. Tap send.
6. Error appears: "Failed to send message — The request was invalid". No message echoes into the transcript.

The session ID is minted (visible in the header, e.g. cc-rh-austin:renfroe-holdings:95f9). Failure is on the first message, not on session create.

Scope

• Reproduces on every environment / repo in the picker.
• Web app (claude.ai/code) does NOT reproduce — same account, same environments, "+" works fine.
• Existing sessions in the mobile sidebar work normally — only the "+" create flow is broken.

Server-side evidence

I run claude-rc listeners on a homelab VM (cc-rh-austin). During the failure, the relevant listener's reported Capacity did not increment — the listener never received a spawn request for the minted session ID. That places the rejection upstream of the listener, on the Anthropic backend, before it asked the host to spawn the child claude.exe.

Timestamp / account

• 2026-06-13 ~09:27 UTC (one specific failed attempt: session id 95f9, env env_01RkALKoGuZrugTue6vdNgT4, repo renfroe-holdings)
• Account: austin@renfroeholdings.com
• iOS app, recent build (will add version next time I open the app)
• Listener host: cc-rh-austin (claude-rc daemon, current build)

Workaround

Use the web app's "+" until patched. Existing mobile sessions still work for non-create operations.