CRITICAL (Opus HALT on prior commit): the PR's edit to save_settings() replaced
'if k in _SETTINGS_ALLOWED_KEYS' with 'if k=="dashboard_plugins": continue' and
orphaned the whole validation body under the continue. Effects: (a) settings save
broken for every key except dashboard_plugins; (b) the allowlist security boundary
gone -> any client key (password_hash, signing_key_*) became settable. Restored the
guard + correct indentation; dashboard_plugins handled by the deep-merge above.
Verified in-process: language persists, password_hash/signing_key injection
rejected, dashboard_plugins still deep-merges.
Also (Opus SHOULD-FIX #3): validate plugin name against ^[a-z][a-z0-9_-]{0,63}$
so a manifest name like '../foo' can't make the URL-space ambiguous.
Regression tests added for both (the allowlist bug had ZERO coverage).
nesquena-hermes
944e739b40