[Bug]: Optional model alias blocks OpenAI-compatible onboarding

Summary

During OpenAI-compatible provider onboarding in OpenClaw Companion, the step labeled Model alias (optional) cannot be submitted with an empty value because the Continue button is disabled.

The field is optional in the Gateway onboarding flow, so users should be able to leave it blank.

Steps to reproduce

1. Start OpenClaw Companion onboarding.
2. Choose the OpenAI-compatible/custom provider path.
3. Complete the endpoint, API key, compatibility, model ID, and endpoint ID steps.
4. Reach Model alias (optional).
5. Leave the field empty.

Actual behavior

Continue remains disabled. Entering an alias is required to proceed despite the field being labeled optional.

Expected behavior

Continue remains available and submits the empty string to the Gateway. The Gateway should remain authoritative for text-field validation so it can accept optional empty values and return its own validation message for required fields.

Current-main evidence

Current Companion main still treats every text wizard step as requiring non-whitespace input in WizardSelection.ShouldDisableContinue, and WizardPage.UpdateContinueState uses that gate for all text steps. The Gateway wizard protocol does not currently expose whether an individual text step is required.

A local patch and regression tests are prepared. The patch also handles the Gateway's successful non-terminal validation response (error plus the same step) so required-field errors remain visible, entered text is preserved, and rejected answers are not appended to the transcript.

Environment

• Surface: OpenClaw Companion onboarding on Windows
• Flow: OpenAI-compatible/custom model provider
• Observed: September 5, 2026
• Current repository main inspected at 305bb4ef5334ded9f8541aca19c66ba2c4b08754

Additional context

The original observation included a screenshot showing the empty Model alias (optional) field with a disabled Continue button. The screenshot is not attached here because it was shared in a separate private conversation and is not being republished without a directly available upload artifact.

Start at WizardSelection.ShouldDisableContinue and WizardPage.UpdateContinueState, then inspect the regression tests mentioned in the issue. Verify that an empty optional alias can be submitted, successful non-terminal validation responses preserve the entered text, and rejected answers are not added to the transcript.