Infer artifact dependencies from configured inputs

internal/config/scriptorium_test.go

@@ -395,7 +395,7 @@ func TestScriptoriumLoadAndValidate(t *testing.T) {
 			wantValidateErr: []string{"pipeline.scriptorium.artifacts.session_recap.output_path", "under artifacts/"},
 		},
 		{
-			name: "missing depends_on for artifact source fails validation",
+			name: "artifact source infers dependency",
 			scriptoriumYAML: `scriptorium:
   binary: scriptorium
   artifacts:
@@ -416,7 +416,13 @@ func TestScriptoriumLoadAndValidate(t *testing.T) {
           source: narratio.artifact.session_recap
           required: true
 `,
-			wantValidateErr: []string{"pipeline.scriptorium.artifacts.player_handout.inputs.recap.source", "requires depends_on"},
+			assert: func(t *testing.T, cfg *Config) {
+				t.Helper()
+				dependencies := cfg.Pipeline.Scriptorium.Artifacts["player_handout"].DependsOn
+				if len(dependencies) != 1 || dependencies[0] != "session_recap" {
+					t.Fatalf("inferred dependencies = %#v, want [session_recap]", dependencies)
+				}
+			},
 		},
 		{
 			name: "dependency on unknown artifact fails validation",