fix: review findings — chain NaN/Inf + id hygiene, percent-escape jobPath, shared singleVideoResult

- SubmitChain rejects NaN/±Inf segment seconds with ErrUnsupported
  (previously an obscure json.Marshal error; NaN fails every comparison
  and +Inf passed the >= 0 check).
- ChainStatus skips segment entries with no usable id — JSON null
  (which no-op-unmarshals into a string, previously appending ""),
  empty strings, and id-less objects; the unfiltered list survives in
  Raw. ChainJob.SegmentIDs doc now also says ChainSegmentResult takes
  the segment index, not an id string.
- jobPath rejects '%' in job ids — %2F/%2E%2E percent-escapes decode
  back into path structure server-side, bypassing the literal check on
  this upstream-echoed value.
- singleVideoResult moves to video.go next to videoMIME, and the two
  remaining hand-rolled copies of the video-result validation
  (videoModel.Generate, Interpolate) now use it — one validation, one
  message shape.
- videogen.LipSyncer renamed to videogen.Lipsyncer for consistency with
  the rest of the surface's Lipsync* naming (LipsyncProvider,
  LipsyncModel, LipsyncRequest); not yet consumed downstream, so the
  rename is free now and never again.

Co-Authored-By: Claude Fable 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01WWCQcYStWXBYUy5sZWnbLT

provider/llamaswap/lipsync.go

@@ -22,7 +22,7 @@ import (
 
 // LipsyncModel implements videogen.LipsyncProvider. The id selects which
 // upstream llama-swap loads.
-func (p *Provider) LipsyncModel(id string, opts ...videogen.LipsyncModelOption) (videogen.LipSyncer, error) {
+func (p *Provider) LipsyncModel(id string, opts ...videogen.LipsyncModelOption) (videogen.Lipsyncer, error) {
 	if err := p.requireBaseURL(); err != nil {
 		return nil, err
 	}
@@ -35,7 +35,7 @@ type lipsyncModel struct {
 	id string
 }
 
-// Lipsync implements videogen.LipSyncer.
+// Lipsync implements videogen.Lipsyncer.
 func (m *lipsyncModel) Lipsync(ctx context.Context, req videogen.LipsyncRequest, opts ...videogen.LipsyncOption) (*videogen.Result, error) {
 	req = req.Apply(opts...)
 	if len(req.Image.Data) == 0 {
@@ -95,19 +95,3 @@ func (m *lipsyncModel) Lipsync(ctx context.Context, req videogen.LipsyncRequest,
 	}
 	return singleVideoResult(m.p.name, m.id, "lipsync", raw, respType)
 }
-
-// singleVideoResult wraps one raw video body into a videogen.Result,
-// requiring positive evidence of video-ness (declared video/* Content-Type
-// or sniffed mp4/webm magic) so a proxy error page can never become "the
-// clip" — the video sibling of singleImageResult.
-func singleVideoResult(provider, model, verb string, raw []byte, contentType string) (*videogen.Result, error) {
-	if len(raw) == 0 {
-		return nil, &llm.APIError{Provider: provider, Model: model, Message: verb + " response contained no video"}
-	}
-	mimeType := videoMIME(contentType, raw)
-	if mimeType == "" {
-		return nil, &llm.APIError{Provider: provider, Model: model,
-			Message: fmt.Sprintf("%s response is not a video (Content-Type %q)", verb, contentType)}
-	}
-	return &videogen.Result{Video: videogen.Video{Data: raw, MIME: mimeType}}, nil
-}