fix(batch): make model field optional on POST /v1/batches

[alexef]

Fixes #3972

Problem

The OpenAI batch spec does not include a model field on POST /v1/batches — the model lives inside each JSONL request body. The standard OpenAI SDK does not send model on batch create.

batchCreate() in handlers/inference.go called resolveModelAndProvider() unconditionally, which returns "model is required" whenever the field is absent:

// before
provider, modelName, err := resolveModelAndProvider(ctx, h.config, req.Model)
if err != nil {
    SendError(ctx, fasthttp.StatusBadRequest, err.Error())  // always fires without model
    return
}

This was a partial miss from PR #1471 — that PR correctly updated the governance plugin to exempt batch requests from model validation, but the HTTP transport handler was not updated. The "model is required" error therefore still fires at the handler layer before governance is ever consulted.

Confirmed against a live deployment (maximhq/bifrost:v1.5.4):

POST /v1/batches   (no model field, x-model-provider: openai header set)
→ 400 {"is_bifrost_error":false,"status_code":400,"error":{"message":"model is required"}}

POST /v1/batches   (with model: "openai/gpt-4o-mini")
→ 200 OK

Fix

When model is absent, resolve the provider from the ?provider= query param or x-model-provider header — the same fallback pattern used by fileUpload. A provider is still required; only the model is now optional.

Testing

• Standard OpenAI SDK batch create (no model field) now succeeds when x-model-provider header is set
• model: "provider/model" still works as before

🤖 Generated with Claude Code

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1 out of 2 committers have signed the CLA.

✅ alexef
❌ akshaydeo
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[greptile-apps]

Confidence Score: 5/5

Safe to merge — the change is narrowly scoped to the batch create handler, preserves all existing model-present behavior, and the new no-model path mirrors an established pattern already in use for file uploads.

The fix is targeted and correct: the new helper correctly delegates to resolveModelAndProvider when a model string is present and handles the no-model case by reading the same provider sources (?provider= / x-model-provider) already used by fileUpload. All four meaningful resolution paths are covered by the new tests, including the error case. No existing behavior is altered.

No files require special attention.

Important Files Changed

Filename	Overview
transports/bifrost-http/handlers/inference.go	Adds resolveBatchProvider helper making model optional on POST /v1/batches; provider is still required via ?provider= or x-model-provider header. Logic correctly mirrors the fileUpload pattern.
transports/bifrost-http/handlers/inference_batch_test.go	New table-driven tests cover all three resolution paths: model present, model absent + header, model absent + query param, and error case when neither is supplied.

_{Reviews (3): Last reviewed commit: "Merge branch 'main' into fix/batch-creat..." | Re-trigger Greptile}

The base branch was changed.