BYOK minimax_api provider cannot work with OpenAI-compatible third-party relay (X-Api-Key hardcoded) - mobile channel messages fail with 'login fail'

Environment

• MiniMax Code 3.0.60, macOS
• minimaxModelSource: minimax_api_key
• A custom provider (openai-completions + Authorization: Bearer) works fine for desktop chat and is the default model

Symptom

Messages sent from the mobile app (connected to desktop) fail with:

BYOK provider minimax_api upstream error: login fail: Please carry the API secret key in the 'X-Api-Key' field of the request header

Root cause analysis (verified against app behavior)

1. The minimax_api provider defaults to https://api.minimaxi.com/anthropic (official endpoint). The configured minimax_api.apiKey is a key for a third-party OpenAI-compatible relay.
2. parseMinimaxApiConfig only accepts apiKey and baseURL — there is no way to configure a custom auth header for the upstream.
3. The SDK's apiKeyAuth sends the key as X-Api-Key header, but the relay only accepts Authorization: Bearer (verified: X-Api-Key → 401 Missing API key; Bearer → 200 OK). The relay does expose an Anthropic-compatible endpoint (/v1/messages).
4. In the same turn, custom_provider:minimax-2 (openai-completions, Bearer) succeeds while minimax_api fails — some mobile-channel requests resolve to the unprefixed builtin MiniMax model and hit minimax_api.

Expected behavior

• Allow minimax_api (or custom providers) to configure auth as Authorization: Bearer / authToken, so BYOK users with third-party relays can use them for the mobile channel.
• Or: mobile-channel auxiliary requests should use the same custom_provider model as the main conversation instead of falling back to minimax_api.

Logs

~/.minimax/v2/observability/logs/runtime-2026081123.log — entries BYOK provider minimax_api upstream error: login fail: ... at 23:40 / 23:45 / 23:47

Start at parseMinimaxApiConfig and apiKeyAuth, then trace how mobile-channel requests resolve the unprefixed MiniMax model versus custom_provider:minimax-2. Use the listed runtime log entries to reproduce the failure. Done means the mobile channel can use the configured relay with Bearer authentication or consistently uses the selected custom provider without falling back to minimax_api.