Solution for 5b16d80c-7004-4e4d-b1f6-992ded2abb73: Define the referenced variables in the container environment (.env plus compose

## Cause initializeCustomEndpoint runs extractEnvVariable on apiKey and baseURL, then tests CUSTOM_API_KEY and CUSTOM_BASE_URL against envVarRegex (/^\${(.+)}$/); a match means the env var was unset and an Error is thrown. ## Steps 1. Identify the endpoint name in the error and the ${...} placeholder in librechat.yaml. 2. Set the variable in .env and ensure docker-compose passes env_file to the api service. 3. Restart LibreChat api and retry the endpoint. 4. If intentional, replace the placeholder with a literal key or user_provided flow per endpoint docs. ## Expected result extractEnvVariable resolves apiKey and baseURL to non-placeholder strings; chat requests proceed without Missing API Key/Base URL errors. ## Misleading approaches - Setting variables only on the host shell without loading them into the container process environment. - Expecting LibreChat to read secrets from librechat.yaml without ${} substitution when user_provided is required. ## Limitations - Partial substitution in strings can leave embedded ${VAR} segments if some vars are unset. - Sensitive infrastructure vars listed in isSensitiveEnvVar are not expanded from placeholders. ## Evidence claims - (documented_platform_behavior) After env substitution, apiKey or baseURL still matching envVarRegex causes throw with "Missing API Key for <endpoint>." or "Missing Base URL for <endpoint>." — https://raw.githubusercontent.com/danny-avila/LibreChat/main/packages/api/src/endpoints/custom/initialize.ts - (documented_platform_behavior) envVarRegex is /^\${(.+)}$/ and extractEnvVariable returns the original placeholder when process.env[varName] is unset for a whole-string placeholder. — https://raw.githubusercontent.com/danny-avila/LibreChat/main/packages/data-provider/src/utils.ts