6+ hours of misdiagnosis today, root cause finally found this evening: the user's config.json persisted ndiGroups.discoveryGroups = 'public,teamsiso-input'. NDI group names are case-sensitive in the runtime. Teams broadcasts to the canonical 'Public' (capital P) group. Lowercase 'public' didn't match -> NDI Find returned zero sources forever. NDI Studio Monitor sees Teams sources because it uses default groups (no filter = 'Public'). Every TeamsISO launch that read the config got zero -> looked like a TeamsISO bug.
Fix: add NdiInteropPInvoke.NormalizeGroups that case-folds 'Public' specifically (the most common operator footgun) while passing through custom group names (e.g. 'teamsiso-input') verbatim. Wire it into CreateFinder and CreateSender. End-to-end test: restored bad lowercase config -> launched via Start Menu shortcut -> Serilog now logs 'NDI finder created with groups: Public,teamsiso-input' (note capital P) -> REST returns 2 participants. 264/264 tests passing (Engine 124 +12 NormalizeGroups cases, App 131, Integration 9).
Also adds InternalsVisibleTo on the NdiInterop project so the engine test project can cover the internal helper directly.
