Missing configuration error when ESLint cannot resolve config file in flat‑config mode

Determine whether ESLint can guarantee a safe rollback of configuration changes when switching between flat‑config mode and the legacy .eslintrc format without altering the resolved rule set, ignores, or language options for a given file.

Flat‑config does not cascade like .eslintrc, the discovered config file is used for that run, and file/ignore paths are interpreted relative to the config file location. The active configuration also depends on the current working directory and an explicit --config flag, while rule defaults and parser/plugin versions may differ between ESLint releases. Until the project decides whether legacy .eslintrc remains a temporary escape hatch or is removed entirely, a config rollback is not safely reversible across the two modes.

• Should ESLint treat legacy .eslintrc as a first‑class config source that can be safely rolled back to flat‑config without changing behavior?
• Is there a versioned compatibility layer that ensures identical resolved configurations when switching between the two modes?
• What verification steps are needed to confirm that a config rollback preserves lint results across flat‑config and .eslintrc modes?