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_test.go

@@ -5,6 +5,7 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"errors"
+	"math"
 	"net/http"
 	"net/http/httptest"
 	"reflect"
@@ -111,6 +112,17 @@ func TestSubmitChainRejectsBadArgs(t *testing.T) {
 	}); !errors.Is(err, llm.ErrUnsupported) {
 		t.Errorf("negative seconds: err = %v, want ErrUnsupported", err)
 	}
+	for name, bad := range map[string]float64{
+		"NaN":  math.NaN(),
+		"+Inf": math.Inf(1),
+		"-Inf": math.Inf(-1),
+	} {
+		if _, err := ch.SubmitChain(context.Background(), videogen.ChainRequest{
+			Segments: []videogen.ChainSegment{{Prompt: "x", Seconds: bad}},
+		}); !errors.Is(err, llm.ErrUnsupported) {
+			t.Errorf("%s seconds: err = %v, want ErrUnsupported", name, err)
+		}
+	}
 }
 
 func TestSubmitChainRejectsMissingJobID(t *testing.T) {
@@ -175,6 +187,27 @@ func TestChainStatusToleratesObjectSegments(t *testing.T) {
 	}
 }
 
+func TestChainStatusSkipsIDLessSegments(t *testing.T) {
+	// null, "", an id-less object, and a mistyped entry must all be
+	// skipped — never appended as "" (SegmentIDs promises fetchable
+	// artifacts; the unfiltered list stays in Raw).
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, _ = w.Write([]byte(`{"status":"running","segment":3,"total":5,` +
+			`"segments":[null,"seg-0","",{},{"id":"seg-1"},{"segment_id":""},42]}`))
+	}))
+	defer srv.Close()
+
+	p := New(WithBaseURL(srv.URL), WithHTTPClient(srv.Client()))
+	ch, _ := p.ChainerModel("videoutils")
+	job, err := ch.ChainStatus(context.Background(), "job-123")
+	if err != nil {
+		t.Fatalf("ChainStatus: %v", err)
+	}
+	if !reflect.DeepEqual(job.SegmentIDs, []string{"seg-0", "seg-1"}) {
+		t.Errorf("SegmentIDs = %v, want [seg-0 seg-1]", job.SegmentIDs)
+	}
+}
+
 func TestChainStatusRejectsStatuslessPayload(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		_, _ = w.Write([]byte(`{"detail":"no such job"}`))
@@ -193,7 +226,7 @@ func TestChainStatusRejectsStatuslessPayload(t *testing.T) {
 func TestChainJobPathRejectsHostileIDs(t *testing.T) {
 	p := New(WithBaseURL("http://unused"))
 	ch, _ := p.ChainerModel("videoutils")
-	for _, bad := range []string{"", "a/b", "a?b", "a#b", "..", "a..b"} {
+	for _, bad := range []string{"", "a/b", "a?b", "a#b", "..", "a..b", "a%2Fb", "%2e%2e", "a%b"} {
 		if _, err := ch.ChainStatus(context.Background(), bad); err == nil {
 			t.Errorf("ChainStatus(%q) succeeded; want error", bad)
 		}