features.token_budget.auto_compact_fallback_prompt must not

Error message

features.token_budget.auto_compact_fallback_prompt must not exceed {AUTO_COMPACT_FALLBACK_PROMPT_MAX_BYTES} bytes

What it means

Error "features.token_budget.auto_compact_fallback_prompt must not exceed {AUTO_COMPACT_FALLBACK_PROMPT_MAX_BYTES} bytes" thrown in openai/codex.

Source

Thrown at codex-rs/core/src/config/mod.rs:1172

        if self
            .guidance_message
            .as_ref()
            .is_some_and(|message| message.len() > TOKEN_BUDGET_GUIDANCE_MESSAGE_MAX_BYTES)
        {
            return Err(std::io::Error::new(
                std::io::ErrorKind::InvalidInput,
                format!(
                    "features.token_budget.guidance_message must not exceed {TOKEN_BUDGET_GUIDANCE_MESSAGE_MAX_BYTES} bytes"
                ),
            ));
        }

        if self
            .auto_compact_fallback_prompt
            .as_ref()
            .is_some_and(|prompt| prompt.len() > AUTO_COMPACT_FALLBACK_PROMPT_MAX_BYTES)
        {
            return Err(std::io::Error::new(
                std::io::ErrorKind::InvalidInput,
                format!(
                    "features.token_budget.auto_compact_fallback_prompt must not exceed {AUTO_COMPACT_FALLBACK_PROMPT_MAX_BYTES} bytes"
                ),
            ));
        }
        if self.auto_compact_fallback_prompt.is_some()
            && self.auto_compact_fallback_buffer_tokens.is_none()
        {
            return Err(std::io::Error::new(
                std::io::ErrorKind::InvalidInput,
                "features.token_budget.auto_compact_fallback_buffer_tokens is required when auto_compact_fallback_prompt is set",
            ));
        }
        if self
            .auto_compact_fallback_buffer_tokens
            .is_some_and(|tokens| tokens <= 0)
        {

View on GitHub (pinned to 339751715c)

Solutions

Shorten auto_compact_fallback_prompt to fit under the byte cap.

When it happens

Trigger: Thrown at codex-rs/core/src/config/mod.rs:1172 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of openai/codex@339751715c (2026-08-25). Data as JSON: /api/errors/c9814aa95e31eb74. Report an issue: GitHub.