### Summary Move Rails Code Suggestions completions from `/v2/code/completions` to `/v4/code/suggestions`. Ensure payloads are updated from the deprecated v2 and correctly sent as v4 format payloads. ### Scope - Create a builder that constructs a `code_editor_completion` prompt component payload for `/v4/code/suggestions` from the existing completion context. - Review v2 completion post-processing (provider adapters, scoring, rewrites) and port required behavior to the v4 path or document what is intentionally dropped. - Use a feature flag to switch `CodeSuggestions::Tasks::CodeCompletion` from the v2 endpoint to v4.