V3 deterministic code format-check capability pack. By-value connector composition (service_kind=cli, no separate ingredient): one local prettier CLI ingredient exposes bounded project operations for readiness and formatting diagnostics. Format checks run from an explicit project directory cwd supplied at execution time, accept one trusted source path, return human-readable diagnostics, avoid caller-supplied Prettier flags, avoid shell wrappers, and never write files. Fixed-function and reproducible: no write mode, no caller-supplied config path, no editorconfig lookup, no stdin stream, no parser/plugin override, no cache, no environment override, no arbitrary command execution, and no network egress. Formatting findings are represented as text output instead of failing the op; real Prettier errors still fail. Requires prettier on PATH. Local and no-egress.