[Bug]: Quota-limited previous-model compact blocks Sol → routed DeepSeek handoff after manual /compact succeeds #2723

Client or integration

Codex App (Desktop) through OpenCodex loopback proxy integration.

Area

Proxy and routing

Summary

A thread that previously used gpt-5.6-sol can be switched in-place to the routed model deepseek/deepseek-v4-flash, and a manual /compact succeeds with the current routed DeepSeek model. However, the next normal user turn triggers Codex's pre-sampling previous-model compaction. The first compaction attempt intentionally uses the previous model (gpt-5.6-sol). If the Sol/ChatGPT quota is exhausted, OpenCodex records that compact attempt as an upstream failure and the turn stops before the current routed DeepSeek model can continue.

Observed failing compact record:

provider=openai
model=gpt-5.6-sol
status=502
code=upstream_server_error
termination=incomplete
error=The usage limit has been reached

No subsequent compact retry to deepseek/deepseek-v4-flash was observed for that blocked turn.

This report is not claiming that the first previous-model compact attempt is incorrect. Upstream Codex intentionally performs previous-model pre-sampling compaction during some model transitions. The compatibility problem is that, through OpenCodex's same-thread routed-model setup, a quota failure on the previous OpenAI model prevents the handoff to the already-working current routed model.

Upstream Codex has also broadened previous-model compact fallback to include usage-limit, unexpected-status, server and exhausted-retry failures:

• fix: retry rejected previous-model compaction with selected model openai/codex#30319
• Broaden remote compaction model fallback openai/codex#32881

Expected OpenCodex behavior is one of the following, depending on what context is available at the proxy layer:

1. Preserve/translate the previous-model quota failure so Codex can trigger its selected/current-model compact fallback; or
2. provide an equivalent OpenCodex compatibility fallback from the unavailable previous route to the current routed model; or
3. if neither is safe, surface/document this limitation explicitly instead of leaving the routed thread blocked by the previous provider's quota.

Reproduction

1. Run OpenCodex 2.31.0 with Codex App loopback integration and a routed DeepSeek model available as deepseek/deepseek-v4-flash.
2. Start or resume a thread that has been using gpt-5.6-sol.
3. Exhaust the ChatGPT/OpenAI usage allowance for gpt-5.6-sol.
4. In the same thread, switch the current model to deepseek/deepseek-v4-flash.
5. Run /compact manually.
6. Observe that manual compaction succeeds with the current routed model.
7. Send a normal user message to continue the thread.
8. Codex performs pre-sampling model-transition compaction against the previous model gpt-5.6-sol.
9. OpenCodex records the compact request as provider=openai, model=gpt-5.6-sol, status=502, error=The usage limit has been reached.
10. The turn stops; no DeepSeek compact fallback is observed.
11. After the Sol quota resets, the same model-switch workflow can continue normally again.

This reproduces a narrow handoff failure: DeepSeek compaction itself is usable, but the previous-model pre-sampling compact failure blocks continuation before the routed current model gets control.

Version

OpenCodex 2.31.0

Operating system

Windows x64 (NT 10.0; exact edition/build not captured)

Provider and model

Previous model/provider:

OpenAI / ChatGPT
model=gpt-5.6-sol

Current routed model:

DeepSeek via OpenCodex
model=deepseek/deepseek-v4-flash

Logs or error output

Error running remote compact task: stream disconnected before completion:
stream closed before response.completed

Matching OpenCodex usage record at the compact failure timestamp:

provider=openai
model=gpt-5.6-sol
status=502
code=upstream_server_error
termination=incomplete
error=The usage limit has been reached

Control observation:

manual /compact on current routed DeepSeek -> succeeds
next normal turn -> previous-model Sol pre-compact -> quota failure -> turn blocked
Sol quota reset -> model-switch workflow works again

Screenshots and supporting files

Relevant upstream Codex behavior/fixes:

• Previous-model compaction with selected-model fallback: fix: retry rejected previous-model compaction with selected model openai/codex#30319
• Broadened fallback for usage-limit/server/retry failures: Broaden remote compaction model fallback openai/codex#32881

Relevant OpenCodex compact routing implementation:

• https://github.com/lidge-jun/opencodex/blob/main/src/server/responses/compact.ts

Redacted configuration

{
  "note": "Credentials, account identifiers, unrelated providers, and secrets removed",
  "routedModel": "deepseek/deepseek-v4-flash",
  "integration": "Codex App loopback proxy"
}

Checks

• I searched existing issues and documentation.
• I removed secrets, tokens, account details, request credentials, and personal data.