feat(videogen): canonical video-generation surface + llama-swap client

New videogen/ contract package (ADR-0019): Request/Result/Model/Provider
with the imagegen conventions. Text-to-video and image-to-video are one
surface (Request.InitImage, nil = t2v) since hybrid checkpoints like
Wan 2.2 TI2V serve both from one model; Result carries a single clip.

provider/llamaswap gains VideoModel(id) targeting the blocking
POST {base}/v1/videos/sync (multipart, model-routed by the fork's new
video routes): vLLM-Omni parameter names, OpenAI-style input_reference
file part, optional fields stay off the wire so per-model launch-flag
defaults apply. CLAUDE.md package map picks up audio/ (missed in #12)
and videogen/.

Co-Authored-By: Claude Fable 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01AXQxVhXBw8PwFAtsVrXSmj

provider/llamaswap/video.go

@@ -0,0 +1,177 @@
+package llamaswap
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"mime"
+	"mime/multipart"
+	"net/http"
+	"strconv"
+	"strings"
+
+	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
+	"gitea.stevedudenhoeffer.com/steve/majordomo/videogen"
+)
+
+// VideoModel implements videogen.Provider, binding a video-generation model
+// served by llama-swap (routed to a vLLM-Omni-style upstream, or any shim
+// exposing the same /v1/videos/sync shape). The id is passed through verbatim
+// and selects which upstream llama-swap loads.
+func (p *Provider) VideoModel(id string, opts ...videogen.ModelOption) (videogen.Model, error) {
+	if err := p.requireBaseURL(); err != nil {
+		return nil, err
+	}
+	_ = videogen.ApplyModelOptions(opts)
+	return &videoModel{p: p, id: id}, nil
+}
+
+type videoModel struct {
+	p  *Provider
+	id string
+}
+
+// Generate implements videogen.Model via POST {base}/v1/videos/sync
+// (multipart/form-data — llama-swap routes by the `model` form field). The
+// blocking sync endpoint answers with the encoded video itself, so the
+// response body is the result; there is no job id to poll. Generation runs
+// for minutes — the provider client carries no timeout by design, and callers
+// bound the call with a context deadline.
+//
+// Parameter names follow vLLM-Omni's videos API (num_frames, fps,
+// num_inference_steps, guidance_scale); the conditioning frame is sent as an
+// `input_reference` file part, following OpenAI's videos API. Upstreams
+// ignore fields they don't understand, and optional fields stay off the wire
+// entirely so the model's own defaults apply.
+func (m *videoModel) Generate(ctx context.Context, req videogen.Request, opts ...videogen.Option) (*videogen.Result, error) {
+	req = req.Apply(opts...)
+	if strings.TrimSpace(req.Prompt) == "" {
+		return nil, fmt.Errorf("%w: video generation requires a prompt", llm.ErrUnsupported)
+	}
+	if req.NumFrames < 0 {
+		return nil, fmt.Errorf("%w: video frame count must be >= 0, got %d", llm.ErrUnsupported, req.NumFrames)
+	}
+	if req.FPS < 0 {
+		return nil, fmt.Errorf("%w: video fps must be >= 0, got %d", llm.ErrUnsupported, req.FPS)
+	}
+	if req.InitImage != nil && len(req.InitImage.Data) == 0 {
+		return nil, fmt.Errorf("%w: video init image has no bytes", llm.ErrUnsupported)
+	}
+	width, height, err := parseSize(req.Size)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %v", llm.ErrUnsupported, err)
+	}
+
+	var buf bytes.Buffer
+	w := multipart.NewWriter(&buf)
+	// Required fields always go on the wire (an empty model id should fail
+	// loudly upstream, not silently vanish); optional ones only when set.
+	fields := []struct {
+		key, value string
+		required   bool
+	}{
+		{"model", m.id, true},
+		{"prompt", req.Prompt, true},
+		{"negative_prompt", req.NegativePrompt, false},
+		{"width", formatInt(width), false},
+		{"height", formatInt(height), false},
+		{"num_frames", formatNonZero(req.NumFrames), false},
+		{"fps", formatNonZero(req.FPS), false},
+		{"num_inference_steps", formatInt(req.Steps), false},
+		{"guidance_scale", formatFloat(req.GuidanceScale), false},
+		{"seed", formatInt64(req.Seed), false},
+	}
+	for _, f := range fields {
+		if !f.required && f.value == "" {
+			continue
+		}
+		if err := w.WriteField(f.key, f.value); err != nil {
+			return nil, fmt.Errorf("llama-swap: build video form: %w", err)
+		}
+	}
+	if req.InitImage != nil {
+		fw, err := w.CreateFormFile("input_reference", initImageFilename(req.InitImage.MIME))
+		if err != nil {
+			return nil, fmt.Errorf("llama-swap: build video form: %w", err)
+		}
+		if _, err := fw.Write(req.InitImage.Data); err != nil {
+			return nil, fmt.Errorf("llama-swap: build video form: %w", err)
+		}
+	}
+	if err := w.Close(); err != nil {
+		return nil, fmt.Errorf("llama-swap: build video form: %w", err)
+	}
+
+	videoBytes, contentType, err := m.p.doRaw(ctx, http.MethodPost, "/v1/videos/sync", m.id, w.FormDataContentType(), &buf)
+	if err != nil {
+		return nil, err
+	}
+	if len(videoBytes) == 0 {
+		return nil, &llm.APIError{Provider: m.p.name, Model: m.id, Message: "video response contained no video"}
+	}
+	return &videogen.Result{Video: videogen.Video{Data: videoBytes, MIME: videoMIME(contentType, videoBytes)}}, nil
+}
+
+// videoMIME resolves the result MIME type: the response Content-Type when it
+// is a concrete video type, else content sniffing, else video/mp4 (the
+// endpoint's default container).
+func videoMIME(contentType string, data []byte) string {
+	if mt, _, err := mime.ParseMediaType(contentType); err == nil && strings.HasPrefix(mt, "video/") {
+		return mt
+	}
+	if mt := http.DetectContentType(data); strings.HasPrefix(mt, "video/") {
+		return mt
+	}
+	return "video/mp4"
+}
+
+// initImageFilename picks the multipart filename hint for the conditioning
+// frame from its MIME subtype. The name is provider-chosen (never
+// caller-supplied), so no sanitization is needed.
+func initImageFilename(mimeType string) string {
+	mt := strings.ToLower(strings.TrimSpace(mimeType))
+	if parsed, _, err := mime.ParseMediaType(mt); err == nil {
+		mt = parsed
+	}
+	switch mt {
+	case "image/jpeg", "image/jpg":
+		return "frame.jpg"
+	case "image/webp":
+		return "frame.webp"
+	default: // stable-diffusion outputs and unknowns: PNG is the safe hint
+		return "frame.png"
+	}
+}
+
+// formatInt renders an optional int pointer for a form field; nil = "" (omit).
+func formatInt(v *int) string {
+	if v == nil {
+		return ""
+	}
+	return strconv.Itoa(*v)
+}
+
+// formatInt64 renders an optional int64 pointer for a form field; nil = "" (omit).
+func formatInt64(v *int64) string {
+	if v == nil {
+		return ""
+	}
+	return strconv.FormatInt(*v, 10)
+}
+
+// formatFloat renders an optional float pointer for a form field; nil = "" (omit).
+func formatFloat(v *float64) string {
+	if v == nil {
+		return ""
+	}
+	return strconv.FormatFloat(*v, 'g', -1, 64)
+}
+
+// formatNonZero renders a non-negative int for a form field; 0 = "" (omit,
+// backend default).
+func formatNonZero(v int) string {
+	if v == 0 {
+		return ""
+	}
+	return strconv.Itoa(v)
+}