Codex 0.155.0 requests fail when request compression is enabled

[cyberElar]

Codex 0.155.0 /responses requests fail when zstd request compression is enabled

Environment

• cc-switch-cli: 5.10.5
• Codex CLI: 0.155.0
• Codex app-server: 0.155.0
• Provider: DeepSeek
• Codex route: local proxy on 127.0.0.1:15722
• Model: deepseek-v4-flash

CC Switch proxy configuration includes:

Codex: enabled
127.0.0.1:15722

Routes:
/chat/completions
/v1/chat/completions
/responses
/v1/responses

Problem

With the default Codex configuration, even a simple request fails immediately:

› test

■ Failed to parse the request body as JSON: expected value at line 1 column 1

The failure occurs before model inference.

I initially verified that this was not caused by an app-server version mismatch. Both the CLI and app-server are now running 0.155.0:

cliVersion: 0.155.0
appServerVersion: 0.155.0

The issue still occurs.

Reproduction

Run:

codex

Then send:

test

Result:

Failed to parse the request body as JSON:
expected value at line 1 column 1

Confirmed workaround

Starting Codex with request compression disabled fixes the issue immediately:

codex -c 'features.enable_request_compression=false'

After doing this, the same request works normally through the same CC Switch proxy and the same DeepSeek provider.

The issue can also be avoided permanently with:

[features]
enable_request_compression = false

in ~/.codex/config.toml.

Likely cause

Codex 0.155.0 sends compressed request bodies when request compression is enabled, using zstd through Content-Encoding.

The CC Switch Codex /responses route appears to attempt JSON deserialization before decoding the compressed request body.

This would explain why the parser fails immediately at:

line 1 column 1

rather than failing on a specific JSON field.

The observed request path is approximately:

Codex 0.155.0
    |
    | zstd-compressed Responses request
    v
CC Switch local proxy :15722
    |
    | JSON parsing before decompression
    v
Failed to parse request body as JSON

Expected behavior

When a Codex request contains:

Content-Encoding: zstd

CC Switch should decompress the body before attempting JSON deserialization and Responses-to-Chat conversion.

Actual behavior

The compressed request body appears to be passed directly to the JSON parser, producing:

expected value at line 1 column 1

Additional verification

The following command consistently works:

codex -c 'features.enable_request_compression=false'

while regular:

codex

consistently fails with the JSON parsing error.

This makes request compression the minimal reproducible trigger.