feat: wave-3 image + document surfaces — segmentation, colorize, face restore, ocr (ADR-0023)

- imagegen.Segmenter/SegmentationProvider: prompted mask via
  POST /upstream/<id>/v1/segment (file, prompt[, threshold], output=mask);
  white = prompted region, EditRequest.Mask polarity.
- imagegen.Colorizer/ColorizeProvider: POST /upstream/<id>/v1/colorize.
- imagegen.FaceRestorer/FaceRestoreProvider:
  POST /upstream/<id>/v1/restore_faces (upscale 1|2).
- New ocr leaf package (Request/Page/Result, Recognize) + llamaswap
  OCRModel: POST /upstream/<id>/v1/ocr (file[, langs, max_pages]),
  tolerant per-page decode (join lines when page text absent), Raw
  escape hatch.
- httptest contract tests per surface; ADR-0023; ADR index backfilled
  (0020-0022 rows were missing).

Co-Authored-By: Claude Fable 5 <[email protected]>

provider/llamaswap/segment.go

@@ -0,0 +1,76 @@
+// segment.go implements imagegen.SegmentationProvider against a
+// GroundingDINO+SAM shim (segment-langsam) reached through llama-swap's
+// /upstream passthrough (ADR-0023):
+//
+//	POST /upstream/<id>/v1/segment   multipart file,prompt[,threshold],output=mask
+//
+// The response is a single grayscale mask PNG where WHITE marks the prompted
+// region — directly usable as imagegen.EditRequest.Mask (white = repaint).
+// The shim also offers output=cutout|boxes; this client always requests the
+// mask, because a cutout is derivable client-side from mask+original with no
+// second GPU call.
+package llamaswap
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"strconv"
+
+	"gitea.stevedudenhoeffer.com/steve/majordomo/imagegen"
+	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
+)
+
+// SegmentationModel implements imagegen.SegmentationProvider. The id selects
+// which upstream llama-swap loads.
+func (p *Provider) SegmentationModel(id string, opts ...imagegen.SegmentationModelOption) (imagegen.Segmenter, error) {
+	if err := p.requireBaseURL(); err != nil {
+		return nil, err
+	}
+	_ = imagegen.ApplySegmentationModelOptions(opts)
+	return &segmentationModel{p: p, id: id}, nil
+}
+
+type segmentationModel struct {
+	p  *Provider
+	id string
+}
+
+// Segment implements imagegen.Segmenter.
+func (m *segmentationModel) Segment(ctx context.Context, req imagegen.SegmentationRequest, opts ...imagegen.SegmentationOption) (*imagegen.Result, error) {
+	req = req.Apply(opts...)
+	if len(req.Image.Data) == 0 {
+		return nil, fmt.Errorf("%w: segmentation requires an image", llm.ErrUnsupported)
+	}
+	if req.Prompt == "" {
+		return nil, fmt.Errorf("%w: segmentation requires a prompt", llm.ErrUnsupported)
+	}
+	if req.Threshold < 0 || req.Threshold > 1 {
+		return nil, fmt.Errorf("%w: segmentation threshold must be in [0,1], got %g", llm.ErrUnsupported, req.Threshold)
+	}
+	path, err := upstreamPath(m.id, "/v1/segment")
+	if err != nil {
+		return nil, err
+	}
+	threshold := ""
+	if req.Threshold != 0 {
+		threshold = strconv.FormatFloat(req.Threshold, 'g', -1, 64)
+	}
+	body, contentType, err := buildMultipart("build segment form",
+		filePart{field: "file", filename: "image.png", data: req.Image.Data},
+		[]formField{
+			{"prompt", req.Prompt, true},
+			{"threshold", threshold, false},
+			// Always the mask: white = prompted region, EditRequest.Mask
+			// polarity. Cutouts are derived client-side.
+			{"output", "mask", true},
+		})
+	if err != nil {
+		return nil, err
+	}
+	raw, respType, err := m.p.doRaw(ctx, http.MethodPost, path, m.id, contentType, body, maxImageResponseBytes)
+	if err != nil {
+		return nil, err
+	}
+	return singleImageResult(m.p.name, m.id, "segmentation", raw, respType)
+}