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Camera-owned native DRM preview

Version 0.111 adds an explicit drm-async Camera preview backend. It uses the same Home KMS implementation and bounded serial executor as DrmPreview.

camera.startPreview({
  backend: 'drm-async',
  stream: 'main',
  drm: { card: '/dev/dri/card1', timeoutMs: 1000 },
})
await camera.setPreviewViewAsync({ window: { width: 1280, height: 720 } })
await camera.setPreviewStreamAsync('lores')
await camera.drainPreviewAsync()
await camera.stopPreviewAsync()

Open and initial empty-plane view setup are synchronous. Subsequent frame, view, background, drain and device-close operations run on the native worker. RGB16/BGR16 inputs additionally support an explicit driver-buffer copy policy. The legacy drm, SDL and headless backends keep their existing behavior. The new asynchronous Camera methods also serialize SDL/headless transitions; they do not move SDL calls off the Bun thread.

Camera admits one outstanding native frame operation. A new pump frame is skipped for display while that operation is pending; capture and recorder consumers can progress using remaining camera buffers. previewInfo() includes owned workerFrames offered/completed/skipped counters and native drmQueue telemetry. These counters describe display admission, not sensor frame loss or physical display FPS. Native DRM state remains a last-completed-operation snapshot. Frame exports pin source owners before the pump releases its frame.

Camera view, stream, drain and stop jobs have a separate bounded FIFO of 32 unfinished operations. Admission is checked again after application signal-listener registration, including stop, queue-fill and mode-reservation reentry. Options are copied at admission; an omitted stream-change view inherits the view in effect when that operation executes. Pending jobs pause display feed while capture/recording continue. Queued jobs are cancellable. View/drain cancellation forwards the original reason to the native child; once its operation is claimed, cancellation can fail. Stream replacement and stop become noncancellable after their lifecycle transaction starts. Timeouts therefore do not promise an interruptible kernel ioctl. Use operationDone to join work; completion hooks may call Camera close without joining their own hook promise.

Synchronous view/stream/stop calls reject this worker backend. Across all backends, synchronous view/stream/stop calls also reject pending preview jobs, so they cannot overtake queued asynchronous transitions. DRM overlays, compositor sharing and desktop integration remain unsupported. Existing DRM format, master/unused-plane, linear-layout and cleanup restrictions apply.

Mode jobs first suspend feed and join/close this owned worker, then strongly check camera leases. They never subtract a preview lease count: application owners of the same camera buffer must still block reconfiguration. Permanent, temporary and recorder/group mode transactions restore the preview recipe. Failed admission restores the old view when the camera remains healthy. Stop, close, capture-series cleanup and reconnect join the worker before changing or releasing camera ownership. Independent DrmPreview objects still require their own explicit retirement before camera reconfiguration.

Display failures suspend only preview. Recording can continue if sufficient buffers remain. An uncertain scanout retains its source exports until proven detachment. previewError records display/cleanup failures; previewCleanupPending includes failed preparation owners and retained display owners. Retry stopPreviewAsync() or close() after resolving the display problem. A failed close never makes an uncertain source safe to recycle. An already pending detach with a lost completion proof can still fail after the external fault is resolved; join that attempt, then issue a fresh cleanup retry.

Linux CI uses an independent C DRM UAPI peer, actual file descriptors and actual poll/read flip packets. It covers all twelve formats, withheld flips, Bun heartbeat and capture/recording progress, bounded admission, async UI jobs, caller leases, mode/group restoration, reconnect and cleanup faults. This is protocol and ownership evidence. Physical Pi display, modifier/color acceptance, sensor throughput and matched Picamera2 performance remain unmeasured.