Generic telemetry

docs/CURRENT_SYSTEM_ARCHITECTURE.md

@@ -139,6 +139,8 @@ The input edge writes CPU frames into `InputFrameMailbox`. The current DeckLink
 
 The output edge consumes completed system-memory frames from `SystemFrameExchange`. The current DeckLink backend schedules those frames to DeckLink. If video output is unavailable, the app continues running render cadence, control, preview, telemetry, and logging.
 
+Runtime state exposes backend-neutral output telemetry through `videoOutput`. Portable fields such as `enabled`, `backend`, and `scheduleFailures` stay at that level; backend-specific counters live under `videoOutput.backendMetrics`.
+
 `PreviewWindowThread` is optional and uses a non-consuming system-memory tap. It paints with Win32/GDI on its own thread and skips preview ticks instead of blocking the frame exchange.
 
 Screenshot routes are present in the UI/OpenAPI surface but are not implemented in the current native command path yet.

docs/openapi.yaml

@@ -520,6 +520,8 @@ components:
           $ref: "#/components/schemas/RuntimeStatus"
         video:
           $ref: "#/components/schemas/VideoStatus"
+        videoOutput:
+          $ref: "#/components/schemas/VideoOutputStatus"
         decklink:
           $ref: "#/components/schemas/DeckLinkStatus"
         videoIO:
@@ -561,6 +563,12 @@ components:
           type: number
         enableExternalKeying:
           type: boolean
+        videoInputBackend:
+          type: string
+          enum: [decklink, none]
+        videoOutputBackend:
+          type: string
+          enum: [decklink, none]
         inputVideoFormat:
           type: string
         inputFrameRate:
@@ -589,6 +597,52 @@ components:
           type: number
         modeName:
           type: string
+    VideoOutputStatus:
+      type: object
+      description: Backend-neutral output telemetry. Backend-specific counters live under `backendMetrics`.
+      properties:
+        enabled:
+          type: boolean
+        backend:
+          type: string
+          example: decklink
+        statusMessage:
+          type: string
+        scheduleFailures:
+          type: number
+        completions:
+          type: number
+        late:
+          type: number
+        dropped:
+          type: number
+        backendMetrics:
+          $ref: "#/components/schemas/VideoOutputBackendMetrics"
+    VideoOutputBackendMetrics:
+      type: object
+      description: Backend-specific output metrics. For `decklink`, this contains DeckLink schedule and buffer telemetry.
+      additionalProperties: true
+      properties:
+        bufferedAvailable:
+          type: boolean
+        buffered:
+          type: number
+          nullable: true
+        scheduleCallMs:
+          type: number
+        scheduleLeadAvailable:
+          type: boolean
+        scheduleLeadFrames:
+          type: number
+          nullable: true
+        playbackFrameIndex:
+          type: number
+        nextScheduleFrameIndex:
+          type: number
+        playbackStreamTime:
+          type: number
+        scheduleRealignments:
+          type: number
     DeckLinkStatus:
       type: object
       deprecated: true