jdx/mise · error

action prediction payload is too large

Error message

action prediction payload is too large

What it means

Thrown by validate_action_prediction in the task-action-manifest pipeline (crates/mise-cache-core/src/agent.rs:1814) when a prediction's payload string exceeds MAX_ACTION_PREDICTION_PAYLOAD (256 KiB, defined at agent.rs:23). Each ActionPrediction carries its prediction as a JSON string; the size cap bounds memory/CPU when manifests are merged or persisted. The check runs before the payload is parsed with serde_json, so oversized payloads are rejected without any JSON work.

Source

Thrown at crates/mise-cache-core/src/agent.rs:1814

    {
        bail!("invalid task action identity");
    }
    Ok(())
}

fn validate_action_prediction(prediction: &ActionPrediction) -> Result<()> {
    prediction.invocation.validate()?;
    prediction.action.validate()?;
    if prediction.adapter.is_empty()
        || !prediction
            .adapter
            .bytes()
            .all(|byte| byte.is_ascii_alphanumeric() || matches!(byte, b'-' | b'_'))
    {
        bail!("invalid action prediction adapter");
    }
    if prediction.payload.len() > MAX_ACTION_PREDICTION_PAYLOAD {
        bail!("action prediction payload is too large");
    }
    serde_json::from_str::<serde_json::Value>(&prediction.payload)?;
    Ok(())
}

fn validate_task_manifest(manifest: &TaskActionManifest, task: &str) -> Result<()> {
    if manifest.version != TASK_ACTION_MANIFEST_VERSION || manifest.task != task {
        bail!("task action manifest has an invalid identity");
    }
    if manifest.predictions.len() > MAX_TASK_ACTION_PREDICTIONS {
        bail!("task action manifest contains too many predictions");
    }
    let mut invocations = BTreeMap::new();
    for prediction in &manifest.predictions {
        validate_action_prediction(prediction)?;
        if invocations.insert(&prediction.invocation, ()).is_some() {
            bail!("task action manifest contains duplicate predictions");
        }

View on GitHub (pinned to 6f52dcdf99)

Solutions

1. Shrink the prediction payload to under 256 KiB: store large content as a cache blob (CacheDigest reference) and keep only a pointer/metadata in payload
2. Check what the payload actually contains — if it duplicates file contents, replace it with the digest of the uploaded blob
3. If you control the manifest producer, gzip/compact the JSON or split one huge prediction into several smaller ones (still under the per-prediction cap)
4. If a genuinely larger cap is required, raise MAX_ACTION_PREDICTION_PAYLOAD in a fork and rebuild — there is no runtime knob

Example fix

// before
let prediction = ActionPrediction {
    invocation,
    action,
    adapter: "cargo".into(),
    payload: serde_json::to_string(&entire_tool_output)?, // may exceed 256 KiB
};

// after
let digest = cache.put_blob_bytes(&entire_tool_output_bytes).await?; // store as blob
let prediction = ActionPrediction {
    invocation,
    action,
    adapter: "cargo".into(),
    payload: serde_json::to_string(&serde_json::json!({ "blob": digest }))?,
};

const MAX_ACTION_PREDICTION_PAYLOAD: usize = 256 * 1024;

fn check_payload_size(prediction: &ActionPrediction) -> Result<(), String> {
    if prediction.payload.len() > MAX_ACTION_PREDICTION_PAYLOAD {
        Err(format!("payload is {} bytes, cap is {}", prediction.payload.len(), MAX_ACTION_PREDICTION_PAYLOAD))
    } else {
        Ok(())
    }
}
// run before persist/merge:
for p in &manifest.predictions { check_payload_size(p)?; }

fn is_payload_within_cap(p: &ActionPrediction) -> bool {
    p.payload.len() <= 256 * 1024
}

match merge_task_manifests(task, base, update) {
    Err(e) if e.to_string().contains("payload is too large") => {
        // move oversized content to a blob and rebuild the prediction
        rebuild_prediction_with_blob_reference(update)?;
    }
    other => other?,
}

When it happens

Trigger: Calling any API that persists or merges task action manifests (e.g. merge_task_manifests at agent.rs:1836, which calls validate_task_manifest -> validate_action_prediction) with a manifest whose predictions[i].payload.len() > 262144. Also hit when an external producer of the manifest file writes a large inline payload blob.

Common situations: A task embeds base64-encoded file contents, full environment dumps, or a whole tool output snapshot into prediction.payload instead of referencing blobs by digest; manifests generated by a newer/different tool without the size cap; hand-edited manifest files in the cache directory.

Related errors

• task action manifest has an invalid identity
• task action manifest contains duplicate predictions
• unsupported remote cache digest algorithm
• invalid remote cache digest
• remote cache action keys must use blake3

AI-assisted analysis of jdx/mise@6f52dcdf99 (2026-08-22). Data as JSON: /api/errors/e57a04fa1a9e5e7c. Report an issue: GitHub.