[BUG] Desktop app: two concurrent in-flight prompts in separate tabs deadlock both sessions (macOS)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

Running two chat sessions in two tabs of the same desktop app instance (two separate projects, unrelated work) deadlocks both tabs.

If I have prompts in flight in both tabs at the same time, both tabs hang and neither makes progress. This is order-independent — it does not matter which tab I ran first. To recover I have to stop both tabs; then only one can be retried and run successfully. In effect, only one session can be active at a time.

This appears to be a desktop variant of the concurrent-session interference already reported in #69195 (tool-result corruption) and #75866 (VS Code "database is locked" freezes all sessions). The common thread is that multiple sessions sharing one desktop process interfere with each other.

Account is on an Enterprise license, so per-account token rate limiting is not the cause.

What Should Happen?

Two sessions in separate tabs should process concurrently and independently. Having a prompt in flight in one tab should not block or hang a prompt in another tab.

Error Messages/Logs

No error surfaced — both sessions silently sit in "thinking" mode. ⟨Attach any logs from the app's developer console / log directory if available.⟩

Steps to Reproduce

1. Open the Claude Code desktop app.
2. Open two tabs, each on a different project.
3. Send a prompt in tab 1 (model: Fable 5, high effort).
4. Send a prompt in tab 2 while tab 1's prompt is still in flight.
5. Observe: both tabs hang and neither makes progress. Order does not matter — the same happens regardless of which tab was started first.
6. Recovery: stop both tabs. Retrying one works; two concurrent in-flight prompts always deadlock.

Note: this occurred with the model set to Fable 5 at high reasoning effort in both tabs.

Claude Model

Fable 5 (high effort)

Is this a regression?

No — first time attempting concurrent tabs; no prior working baseline.

Last Working Version

N/A (never worked for me)

Claude Code Version

Desktop app 1.19367.0 (1a5be1)

Platform

Desktop app

Operating System

macOS Tahoe 26.5

Terminal/Shell

N/A (desktop app)

Additional Information

• Enterprise license (rules out per-account rate-limit throttling).
• Both tabs used model Fable 5 at high reasoning effort.
• Reproduced consistently.
• Recovery: both hung tabs had to be stopped; retrying only one then works. Effectively only one session can run at a time.
• Order-independent: the deadlock happens regardless of which tab's prompt was started first.
• Likely related: #69195 (concurrent desktop sessions corrupt tool results), #75866 (concurrent sessions freeze in VS Code extension), #73364 (concurrent sessions clobber ~/.claude.json).
• Workaround found: running each project as a separate claude CLI instance in its own terminal (separate OS processes) ⟨confirm whether this works for you⟩.