Faster prompt A/B testing when a variant label is missing

[jannikmaierhoefer]

Describe the feature or potential improvement

We recommend using prompt labels for A/B tests (see docs: /docs/prompt-management/features/a-b-testing). In practice, some prompts may not have the “B” label (e.g., prob-b) yet.

When the “B” label is missing, users may implement:
try { getPrompt("prob-b") } catch { getPrompt("prod") }

But the failed getPrompt() call can be slow (reported ~2s), which makes prompt resolution expensive in hot paths.

Desired outcome:
Make “label missing” a fast path so A/B prompt resolution is cheap even when variants are not fully configured.

Additional information

No response