Engine: IsoAssignment record gets optional Override (FrameProcessingSettings?). IsoController hydrates _overrides dict from config.json on startup, uses override at EnableIsoAsync, persists with assignment, exposes GetIsoOverride + SetIsoOverrideAsync. SetIsoOverrideAsync hot-swaps a running pipeline (Disable + 150ms delay + Enable) when the override changes.
REST: POST /participants/{id}/override (body: framerate/resolution/aspect/audio enum strings, all optional, missing fall back to globals); DELETE /participants/{id}/override clears. GET /participants now includes per-row effective {framerate, resolution, aspect, audio, isOverride} plus top-level globals block.
Web /ui: per-card collapsible override panel with four selects + Apply / Clear. OVR pill + cyan inset edge mark overridden rows. Open-panel state survives WS re-renders.
Desktop: per-row gear column in the v2 DataGrid opens IsoOverrideDialog (420x360) with four combos. Clear button removes the override.
Thumbnail endpoint switched from WPF JpegBitmapEncoder (NREs from non-UI HttpListener threads) to pure-managed 32bpp BMP encoder. Nearest-neighbor downscale to 192-wide. /participants/{id}/thumbnail.bmp; legacy .jpg URL still works.
Known limitation: ParticipantTracker regenerates IDs for display-name-keyed participants across process restarts, orphaning the persisted override. Override works within a session; cross-restart persistence is best-effort until the tracker is taught to use stable keys. Filed as task 43.
REST additions: GET /topology returns mode (hidden/public/unknown) + sender/receiver group lists. POST /topology/apply confines local senders to teamsiso-input + receivers to public+teamsiso-input. POST /topology/restore returns both to public defaults.
GET /participants/{id}/thumbnail.jpg encodes the latest engine ProcessedFrame as a 192-wide JPEG. 404 when no pipeline is running. Used by the /ui control panel for live preview tiles.
Settings: ControlSurfaceEnabled now persists across sessions via UIPreferences and auto-starts the server on app launch when previously enabled.
/ui control panel rebuilt: live thumbnail per row, topology toggle card with Hide/Restore buttons, removed dead recording marker button, larger layout (920px), participant rows in single card with hover affordances.
