TUI UI deadlocks when switching agent threads while under high CPU+Memory pressure

What version of Codex CLI is running?

0.146.1.322 (stable)

What subscription do you have?

None; using AWS Bedrock (company paid)

Which model were you using?

gpt-5.6-sol

What platform is your computer?

Darwin 25.5.0 arm64 arm

What terminal emulator and version are you using (if applicable)?

Ghostty

Codex doctor report

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}

What issue are you seeing?

When the system is under extreme CPU + memory pressure (2-3 parallel xcodebuild processes each all trying to consume all CPU cores, active processes swapping), the UI can hang.

I'm typically talking to the main agent, and I typically have many subagents open as well. First symptom: messages sent to the main agent are displayed in the UI, but responses back are not displayed (confirmed via jsonl inspection that the main agent does respond, but it does not show in the UI).

If I'm in that no-main-responses showing mode, and I do nothing, it will eventually recover.

If I'm in that no-main-responses showing mode, and I instead switch to another agent, then switch back to main (using /side and exiting /side also works), the UI freezes entirely.

When frozen, the UI seems to not process any input. It does not respond to Ctrl+Q, Ctrl+S, newlines, nor typed messages. It does not re-draw upon terminal resizing. The main agent continues to process new turns, but after the UI freezes, if I type input, even with <Enter> at the end, the main agent does not receive it as a message.

What steps can reproduce the bug?

• Start a codex TUI instance
• Ask it to start a sub-task and keep it open for you to talk to
• Find/download a project with a long (10+ minute) highly parallel compilation. Ensure you have enough system memory to support one compilation, but maybe not enough to support multiple without swapping
• Clone the project into multiple worktrees or directories
• Start compilation in multiple workspaces, continuing to add more until most application UIs become visibly laggy (browsers, terminal, etc. should be taking 0.5 seconds to respond to most UI input)
• Note: it's not entirely clear to me whether it is specifically CPU pressure, or if the multiple app compilations cause memory pressure and slowdown via swapping
• Rapidly swap between the main instance and sub-agent via /agents until UI. Alternatively, rapidly launch /side <some ask> conversations and exit them.

What is the expected behavior?

At all points, the TUI should be responsive. Under no circumstance should it stop processing user input - any continued input processing - even if delayed - is preferred to a complete freeze/deadlock.

Additional information

After experiencing this bug four or five times, I modified codex locally to hook in tokio-console for further diagnosis. I forked off of 79b4f03d35962b005b007a015113b38930711665 / rust-v0.146.1.

I got a codex instance to freeze, then had an LLM analyze it. It produced this timeline and inference:

Precise event timeline

| Time | Type | Event and significance |
| --- | --- | --- |
| 13:24:46.396552625 | Observation | Task 132, the top-level TUI event-loop task, received its last recorded wake. |
| 13:24:47.507392250 to 13:24:47.507410583 | Observation | Task 154, the in-process app-server facade worker, performed its final recorded poll. The broader capture records its wake/poll beginning around 13:24:47.507383. |
| 13:24:47.507399875 to 13:24:47.507419083 | Observation | Task 132 performed its final recorded poll. It ended approximately 8.5 microseconds after task 154's final poll ended. |
| About 13:24:47.508945 to 13:24:47.508983417 | Observation | Task 136, the frame-scheduler task, received and processed its final recorded redraw wake, then became idle. |
| After 13:24:47.508983417 | Observation | Lower in-process app-server tasks 141, 143, and 144 continued polling after the three UI-facing tasks stopped. |
| 13:30:09.395 | Observation | The parent rollout still recorded parent-owned reasoning, messages, and tool activity, rather than only child-process activity. |
| 13:56:57.064 | Observation | The parent rollout recorded a parent send_input call. |
| 13:57:01.105 | Observation | The parent rollout recorded a parent wait_agent call, the latest explicitly verified parent event. |
| 13:59:59.832506 | Observation | The target Codex process remained alive in state S+, using 0.5% CPU with 422,256 KiB RSS. |

Inference: The facade-first, TUI-next ordering is consistent with task 154 becoming pending on one of the awaited outward sends in the lossless-delivery path, followed by task 132 becoming pending on a facade request. The potentially blocked outward item is either a preceding Lagged marker or the lossless event itself.

Timing alone does not identify the awaited Rust future, queue occupancy, outward item, or pending request method. The deadlock hypothesis therefore depends on both the timing evidence, and source analysis.