Codex Desktop turn lifecycle stalls across image and non-image sessions

Summary

Codex Desktop sessions can get stuck indefinitely showing "thinking" / "generating" after a few turns. This is not limited to long-running sessions: I observed it in small/new image sessions as well as in a long non-image session. Local diagnostics indicate multiple turn lifecycle stall modes:

• main turn starts but never reaches a normal completion state
• tool outputs are returned, but the assistant continuation never resumes
• long non-image sessions enter a core unfinished turn state after compaction/prewarm/interruption activity

The user-visible result is that the session remains in a thinking state and no further assistant message appears.

Environment

• Product: Codex Desktop app + Codex CLI
• CLI version: codex-cli 0.128.0-alpha.1
• OS: macOS 15.5, arm64
• Desktop app server observed as: Codex.app ... app-server --analytics-default-enabled
• Main affected model in real sessions: gpt-5.5
• Probe model: gpt-5.4-mini
• GitHub issue report intentionally excludes full transcripts, local private paths, and image files.

Observed cases

Case A: new/small image session, main turn did not complete

• Session type: image-to-cartoon style task
• Session size: small/new session
• Observed diagnostic shape:
  • task_started: 2
  • task_complete: 0
  • user-visible session remained thinking
  • prompt hooks completed normally and did not block
  • later manual abort/interrupt appears in logs

This suggests the main user turn entered Codex core state but did not reach a normal completion/error surface.

Case B: image/pet session, post-tool continuation stalled

• Session type: image-heavy pet asset generation
• Observed diagnostic shape:
  • task_started: 8
  • task_complete: 6
  • last successful events include image generation/tool calls and completed shell command outputs
  • final tool outputs appear after the last assistant message
  • no assistant continuation follows the returned tool outputs

This looks like a post-tool continuation failure: tools returned, but the assistant loop did not resume.

Case C: non-image long session, core turn unfinished

• Session type: assets migration / non-image engineering work
• Observed diagnostic shape:
  • task_started: 119
  • task_complete: 112
  • context_compacted: 13
  • turn_aborted: 6
  • core logs include session startup prewarm and later interrupt/abort activity

This is important because it shows the hang is not only image-related. Image inputs appear to increase the chance of stalls, but a non-image long-context session can also hit the failure mode.

A/B timing probes

All probes were trivial prompts that completed with OK; the point was to compare turn startup/runtime paths.

Interpretation:

• UserPromptSubmit hooks do not explain the core issue: text timing is essentially unchanged when they are disabled.
• Image inputs are a strong latency amplifier even in isolated mode.
• Normal Desktop/user-config runtime adds a large overhead compared with isolated mode.
• shell_snapshot is not the main overhead in this probe.

Additional signal: analytics Cloudflare 403 during isolated runs

Even with --ephemeral --ignore-user-config, Codex emitted warnings that analytics events to:

https://chatgpt.com/backend-api/codex/analytics-events/events

failed with Cloudflare-managed 403/challenge HTML.

The probes still completed, so this may not be the sole blocker, but it is a platform-level failing request outside the user's project code/config and may contribute latency/noise or interact badly with retries in Desktop sessions.

Expected behavior

When Codex cannot continue a turn, it should surface an explicit error, timeout, or cancellation state. A session should not remain indefinitely in a thinking/generating state after:

• the main user turn is accepted
• tool outputs have already returned
• compaction/prewarm/interrupt state occurs

Actual behavior

The app can remain indefinitely in a thinking/generating state with no further assistant output. Depending on the case, the rollout/log evidence shows dangling task_started, returned tool outputs without continuation, or unfinished core turns.

Related issues found before filing

• #20392: dangling task_started hydration issue
• #19980: "thinking... but no output"
• #17728: never ending thinking process
• #14220: hang with parallel long-running tool calls
• #14251: stuck generating after interrupted turn
• #16042: compaction-related regression

This report is filed separately because it includes multiple observed stall modes, an image vs non-image split, and A/B evidence that user prompt hooks are unlikely to be the primary cause.

Privacy note

I can provide specific local thread IDs or redacted rollout snippets privately if useful, but I am not posting complete transcripts or user image assets in this public issue.