p2.1: honcho-embed, wayback http/204, memento, keys owner

Embed requests send dixie.embed_model (default honcho-embed).
Wayback accepts http://web.archive.org, rewrites to https, skips
non-200 closest.status. Memento-Datetime is parsed as an HTTP date
and future/garbage values become empty snapshot_at. keys add writes
via temp+fchown/chmod/rename so root does not clobber keys.toml.
Digest fallback is capped at the 6k-token budget.

internal/digest/digest_test.go

@@ -250,3 +250,42 @@ func TestChunkOrderAndBudget(t *testing.T) {
 		t.Fatal("document order")
 	}
 }
+
+func TestEmbedUsesConfiguredModel(t *testing.T) {
+	var got string
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var body struct {
+			Model string `json:"model"`
+		}
+		_ = json.NewDecoder(r.Body).Decode(&body)
+		got = body.Model
+		_ = json.NewEncoder(w).Encode(map[string]any{
+			"data": []map[string]any{
+				{"index": 0, "embedding": []float64{1, 0}},
+				{"index": 1, "embedding": []float64{0, 1}},
+			},
+		})
+	}))
+	defer ts.Close()
+	e := &Engine{EmbedURL: ts.URL, EmbedModel: "honcho-embed", Client: ts.Client()}
+	if _, err := e.embedBatch(context.Background(), []string{"q", "chunk"}); err != nil {
+		t.Fatal(err)
+	}
+	if got != "honcho-embed" {
+		t.Fatalf("model %q", got)
+	}
+	e.EmbedModel = "other-embed"
+	if _, err := e.embedBatch(context.Background(), []string{"q", "chunk"}); err != nil {
+		t.Fatal(err)
+	}
+	if got != "other-embed" {
+		t.Fatalf("model %q", got)
+	}
+	e.EmbedModel = ""
+	if _, err := e.embedBatch(context.Background(), []string{"q", "chunk"}); err != nil {
+		t.Fatal(err)
+	}
+	if got != "honcho-embed" {
+		t.Fatalf("default model %q", got)
+	}
+}