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/videochain.go

@@ -19,6 +19,7 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
+	"math"
 	"net/http"
 	"strconv"
 	"strings"
@@ -71,8 +72,10 @@ func (m *chainerModel) SubmitChain(ctx context.Context, req videogen.ChainReques
 		if strings.TrimSpace(seg.Prompt) == "" {
 			return "", fmt.Errorf("%w: video chain segment %d requires a prompt", llm.ErrUnsupported, i)
 		}
-		if seg.Seconds < 0 {
-			return "", fmt.Errorf("%w: video chain segment %d seconds must be >= 0, got %g", llm.ErrUnsupported, i, seg.Seconds)
+		// NaN/±Inf would otherwise surface as an obscure json.Marshal error
+		// (NaN fails every comparison; +Inf passes the >= 0 check).
+		if seg.Seconds < 0 || math.IsNaN(seg.Seconds) || math.IsInf(seg.Seconds, 0) {
+			return "", fmt.Errorf("%w: video chain segment %d seconds must be a finite value >= 0, got %g", llm.ErrUnsupported, i, seg.Seconds)
 		}
 		wire.Segments = append(wire.Segments, chainSegmentWire{Prompt: seg.Prompt, Seconds: seg.Seconds})
 	}
@@ -133,10 +136,17 @@ func (m *chainerModel) ChainStatus(ctx context.Context, jobID string) (*videogen
 		Total:   out.Total,
 		Raw:     raw,
 	}
+	// Entries that carry no usable id — JSON null (which unmarshals into a
+	// string as a no-op, leaving ""), an empty string, or an object with
+	// neither key — are SKIPPED, never appended as "": SegmentIDs promises
+	// fetchable artifacts, and the full payload stays in Raw for callers
+	// that want the unfiltered list.
 	for _, entry := range out.Segments {
 		var s string
 		if json.Unmarshal(entry, &s) == nil {
-			job.SegmentIDs = append(job.SegmentIDs, s)
+			if s != "" {
+				job.SegmentIDs = append(job.SegmentIDs, s)
+			}
 			continue
 		}
 		var obj struct {
@@ -197,7 +207,10 @@ func (m *chainerModel) jobPath(jobID, suffix string) (string, error) {
 	if strings.TrimSpace(jobID) == "" {
 		return "", fmt.Errorf("llama-swap: chain job call requires a job id")
 	}
-	if strings.ContainsAny(jobID, "/?#") || strings.Contains(jobID, "..") {
+	// '%' is rejected alongside the literal path characters: job ids never
+	// legitimately carry percent-escapes, and %2F/%2E%2E would decode back
+	// into path structure server-side.
+	if strings.ContainsAny(jobID, "/?#%") || strings.Contains(jobID, "..") {
 		return "", fmt.Errorf("llama-swap: invalid chain job id %q (contains path structure)", jobID)
 	}
 	return upstreamPath(m.id, "/v1/jobs/"+jobID+suffix)