Retry And Fallback

Prompt:

Use nxusKit Examples to find the smallest retry/fallback example and implement that pattern here.

Starter fixture: any fixture with an existing provider call; examples/fixtures/starters/go-service/ is a good target.

Expected behavior:

• Inspect the current provider call first.
• Consult the retry-fallback example.
• Implement the smallest fallback chain that fits the project.
• Preserve existing provider flags and environment variables.
• Add tests for first-provider success, fallback success, all-fail, and empty-chain cases when the project has test coverage.

Verification:

go test ./...
go run . -provider fallback -prompt "Confirm fallback."

Good result:

• Failed providers are reported clearly.
• The first successful provider response is returned.