Pull the modal's non-layout logic into focused files at the form root:
- useSecurityActions.ts: TLS/Reality key + cert generation handlers and
onSecurityChange (consumed by the security tab)
- useInboundFallbacks.ts: fallback row state + load/save/derive/add/
update/remove/move handlers + eligible-child options
- FallbacksCard.tsx: the fallbacks card UI (presentational)
- SniffingTab.tsx: the sniffing tab UI (presentational)
Also drop the stale "Pattern A rewrite / sibling file" header comment and
the imports the extractions made unused. InboundFormModal goes from 1332
to 868 lines with no behavior change (351 tests green, snapshots
unchanged).
