S006 Success Criteria

ID	Criterion
S006-SC-001	Every optional config key MUST have a documented default value, and Settings::fromConfig([]) (empty config) MUST produce a valid Settings object with all defaults applied without throwing any exception.
S006-SC-002	All properties on the Settings DTO MUST be declared public readonly. After construction, no property value can be changed. Attempting to assign a value to any property MUST produce a PHP fatal error.
S006-SC-003	The output of parity init MUST round-trip: parsing the generated file with Yaml::parse() and passing the result to Settings::fromConfig() MUST produce a valid Settings object. Running parity check against the init template (given valid source/test directories and coverage data) MUST NOT produce any config-related errors.
S006-SC-004	A legacy-format structure entry (using source_path/test_path/enforce_attribute/min_coverage) MUST produce the same resolved rules as an equivalent modern-format entry (using paths/rules). Given identical source files and coverage data, the two formats MUST produce identical RuleResult outputs.
S006-SC-005	When a config file contains invalid content (empty file, non-array YAML, unreadable file, missing Symfony Yaml), the system MUST produce an actionable error message that tells the user what went wrong and how to fix it. The system MUST NOT produce an uncaught exception or stack trace for these cases.