feat: media expansion surfaces — edit mask, upscale, background removal, interpolation, diarization, meshgen (ADR-0020)

- imagegen.EditRequest.Mask -> sd-server img2img inpainting (white=repaint)
- imagegen.Upscaler + BackgroundRemover, videogen.Interpolator,
  audio.DiarizationModel: new optional provider-minted surfaces
- NEW meshgen leaf package (image->3D, glb/stl/obj)
- provider/llamaswap: all five via the /upstream/<model>/<path> passthrough
  (upstreamPath helper, shared one-file multipart builder); binary success
  bodies validated (non-image, non-video, JSON-mesh rejection); diarization
  pins output=json (vtt/srt drop speaker labels)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

audio/diarize.go

@@ -0,0 +1,113 @@
+package audio
+
+import "context"
+
+// DiarizationRequest is a speaker-labelled transcription request ("who said
+// what"). Audio is carried as bytes (never a URL), mirroring
+// TranscriptionRequest. Zero values mean "backend default" (ADR-0020).
+type DiarizationRequest struct {
+	// Audio is the encoded audio (or video container) to transcribe.
+	Audio []byte
+
+	// MIME is the audio MIME type (e.g. "audio/mpeg"); "" = let the backend
+	// sniff it.
+	MIME string
+
+	// Filename is the multipart filename hint some backends key their format
+	// detection on; "" derives one from MIME or falls back to "audio".
+	Filename string
+
+	// Language is a BCP-47/ISO-639 hint (e.g. "en"); "" = auto-detect.
+	Language string
+
+	// MinSpeakers / MaxSpeakers bound the speaker count when the caller knows
+	// it; 0 = let the backend estimate.
+	MinSpeakers int
+	MaxSpeakers int
+}
+
+// DiarizationSegment is one speaker turn.
+type DiarizationSegment struct {
+	// Start and End are offsets into the audio, in seconds.
+	Start float64
+	End   float64
+
+	// Speaker is the backend's per-file speaker label (e.g. "SPEAKER_00").
+	// Labels are relative to this one file — they are NOT stable identities
+	// across files.
+	Speaker string
+
+	// Text is the transcript of this turn.
+	Text string
+}
+
+// DiarizationResult is the canonical diarization result.
+type DiarizationResult struct {
+	// Text is the full transcript, unlabelled.
+	Text string
+
+	// Language is the detected (or requested) language code; may be "".
+	Language string
+
+	// Segments are the speaker turns in time order.
+	Segments []DiarizationSegment
+
+	// Raw is the provider-native response object. May be nil.
+	Raw any
+}
+
+// DiarizationOption mutates a DiarizationRequest before it is sent.
+type DiarizationOption func(*DiarizationRequest)
+
+// WithDiarizationLanguage sets the language hint (e.g. "en").
+func WithDiarizationLanguage(l string) DiarizationOption {
+	return func(r *DiarizationRequest) { r.Language = l }
+}
+
+// WithSpeakerBounds bounds the expected speaker count (0 leaves a bound
+// unset).
+func WithSpeakerBounds(minSpeakers, maxSpeakers int) DiarizationOption {
+	return func(r *DiarizationRequest) {
+		r.MinSpeakers, r.MaxSpeakers = minSpeakers, maxSpeakers
+	}
+}
+
+// Apply returns a copy of the request with all options applied.
+func (r DiarizationRequest) Apply(opts ...DiarizationOption) DiarizationRequest {
+	for _, opt := range opts {
+		opt(&r)
+	}
+	return r
+}
+
+// DiarizationModel transcribes audio with speaker labels.
+type DiarizationModel interface {
+	// Diarize converts the request's audio into speaker-labelled segments.
+	Diarize(ctx context.Context, req DiarizationRequest, opts ...DiarizationOption) (*DiarizationResult, error)
+}
+
+// DiarizationModelOption configures a DiarizationModel at construction time.
+// Reserved for future per-model settings.
+type DiarizationModelOption func(*DiarizationModelConfig)
+
+// DiarizationModelConfig carries per-model construction settings.
+type DiarizationModelConfig struct{}
+
+// ApplyDiarizationModelOptions folds options into a config.
+func ApplyDiarizationModelOptions(opts []DiarizationModelOption) DiarizationModelConfig {
+	var cfg DiarizationModelConfig
+	for _, opt := range opts {
+		opt(&cfg)
+	}
+	return cfg
+}
+
+// DiarizationProvider mints diarization models bound to one backend.
+type DiarizationProvider interface {
+	// Name is the registry identifier for the provider.
+	Name() string
+
+	// DiarizationModel returns a DiarizationModel bound to the given id
+	// (passed through to the backend verbatim; no catalog validation).
+	DiarizationModel(id string, opts ...DiarizationModelOption) (DiarizationModel, error)
+}