fix(wizard): avoid rerunning completed setup steps (#692)

docs/scratchpads/B4-wizard-step-dedup.md

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+# B4 — Wizard step deduplication
+
+## Problem
+
+Greenfield wizard testing showed completed wizard steps could be executed again after the menu marked them `[done]`. In practice this made the Providers/API-key flow and Skills flow appear twice in one wizard run.
+
+There was a second related API-key duplication path: when the Providers step was completed with no key, `gatewayConfigStage` still prompted for `ANTHROPIC_API_KEY` during Finish because it only skipped the gateway API-key prompt when `providerKey` was non-empty.
+
+## Diagnosis
+
+- `runMenuLoop` labeled completed sections with `[done]`, but still dispatched the selected step again if the user selected that row.
+- Quick Start ran Providers and Skills but did not mark those sections complete in `completedSections`.
+- `runFinishPath`/`quickStartPath` defaulted `providerType` to `none` for gateway config, which made it impossible for `gatewayConfigStage` to distinguish:
+  - provider step completed and user intentionally skipped the key, vs.
+  - provider step was never run.
+
+## Fix
+
+- Added a shared menu section key helper and a completed-step guard in `runMenuLoop`.
+- Completed menu steps now log a skip message instead of re-running their stage.
+- Quick Start marks Providers and Skills complete after running them.
+- Finish/Quick Start now pass `state.providerType` as-is to gateway config instead of defaulting to `none`.
+- `gatewayConfigStage` treats `providerType: 'none'` as an explicit completed provider setup with no key and skips the second gateway API-key prompt.
+
+## Verification
+
+- Added unified wizard regression coverage asserting repeated Providers/Skills menu selections only execute each stage once.
+- Added gateway config coverage asserting `providerType: 'none'` does not prompt for a gateway API key and writes no API key env var.
+- Targeted: `pnpm --filter @mosaicstack/mosaic test -- unified-wizard gateway-config`
+- `pnpm format:check`
+- `pnpm typecheck`
+- `pnpm lint`
+- `pnpm build`
+- `pnpm test`
+- Codex code review: approve.
+- Codex security review: no findings.