diff --git a/candy/plugin-media/params/cue_types_gen.go b/candy/plugin-media/params/cue_types_gen.go
index 967a76b..ac22a4f 100644
--- a/candy/plugin-media/params/cue_types_gen.go
+++ b/candy/plugin-media/params/cue_types_gen.go
@@ -32,23 +32,23 @@ type TranscodeInput struct {
 	// capture session flushed). The bed-runner evidence phase threads the entry's
 	// primary artifact here; a direct/plan-step dispatch may set it explicitly.
 	// Empty → the provider falls back to the check env's source_artifact.
-	SourceArtifact string `yaml:"source_artifact,omitempty" json:"source_artifact,omitempty"`
+	SourceArtifact string `json:"source_artifact,omitempty"`
 
 	// to — the CONTAINER FORMAT to transcode the source to. Single-purpose verb:
 	// only "mp4" is supported (the default; an empty/omitted value means mp4). The
 	// transcode is H.264 + yuv420p in an MP4 container, so the artifact plays
 	// everywhere (the ffmpeg argv: -c:v libx264 -pix_fmt yuv420p).
-	To string `yaml:"to,omitempty" json:"to,omitempty"`
+	To string `json:"to,omitempty"`
 
 	// artifact — the HOST path the transcoded file is written to. Empty (the
 	// common case) → derived from the source path by swapping its extension to
 	// ".mp4" (the source MJPEG the capture session flushed is already host-side).
-	Artifact string `yaml:"artifact,omitempty" json:"artifact,omitempty"`
+	Artifact string `json:"artifact,omitempty"`
 
 	// artifact_min_bytes — the post-transcode artifact-reality assertion: the
 	// output MP4 must be at least this many bytes (sdk.RunArtifactValidators,
 	// shared implementation).
-	ArtifactMinBytes int `yaml:"artifact_min_bytes,omitempty" json:"artifact_min_bytes,omitempty"`
+	ArtifactMinBytes int `json:"artifact_min_bytes,omitempty"`
 
 	// artifact_not_uniform — the SOURCE-frame motion assertion (the RDD-3 binding
 	// of the nested-capture plan): evaluated on the SOURCE MJPEG frames (the
@@ -57,5 +57,5 @@ type TranscodeInput struct {
 	// source MJPEG stream into its constituent JPEGs, decodes a stream-wide
 	// sample, and requires at least two distinct frame signatures: identical
 	// frames FAIL honestly (a real capture shows motion), differing frames PASS.
-	ArtifactNotUniform bool `yaml:"artifact_not_uniform,omitempty" json:"artifact_not_uniform,omitempty"`
+	ArtifactNotUniform bool `json:"artifact_not_uniform,omitempty"`
 }
diff --git a/candy/plugin-media/params/decode_test.go b/candy/plugin-media/params/decode_test.go
new file mode 100644
index 0000000..019fd99
--- /dev/null
+++ b/candy/plugin-media/params/decode_test.go
@@ -0,0 +1,118 @@
+package params
+
+// decode_test.go — pins this generated projection against its SOURCE OF TRUTH, in both directions.
+//
+// charly hands a plugin its parameters as JSON (`spec.Op`'s params_json) and the plugin decodes
+// that JSON into this projection; the sdk's kit.DecodeInput re-marshals to JSON before it
+// unmarshals too. No YAML decoder ever sees these types — which is why the projection's `yaml:`
+// tags are inert, and why this test pins the JSON side rather than asserting that claim in prose.
+//
+// The expected keys below are copied from the `#TranscodeInput` definition in
+// `candy/plugin-media/schema/*.cue` — the schema that GENERATES this file. They are hardcoded on
+// purpose: deriving them from the struct's own `json` tags (the obvious thing) makes the test
+// vacuous, because a tag that drifts takes its derived expectation with it and the decode still
+// lines up.
+
+import (
+	"encoding/json"
+	"fmt"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+// schemaKeys is the field set of #TranscodeInput, taken from candy/plugin-media/schema.
+var schemaKeys = []string{
+	"artifact",
+	"artifact_min_bytes",
+	"artifact_not_uniform",
+	"source_artifact",
+	"to",
+}
+
+func TestProjectionMatchesItsSchema(t *testing.T) {
+	rt := reflect.TypeOf(TranscodeInput{})
+	ptr := reflect.New(rt)
+
+	// Direction 1: STRUCT -> SCHEMA. Every exported field must carry a json key the schema
+	// declares; a drifted, emptied or removed tag is caught here.
+	wire := map[string]any{}
+	exported := 0
+	tagOf := map[string]string{} // json key -> Go field name
+	for i := 0; i < rt.NumField(); i++ {
+		f := rt.Field(i)
+		if f.PkgPath != "" {
+			continue // unexported
+		}
+		exported++
+		key := strings.Split(f.Tag.Get("json"), ",")[0]
+		if key == "" || key == "-" {
+			t.Fatalf("field %s carries no usable json tag (%q) — no schema key can reach it", f.Name, key)
+		}
+		if !contains(schemaKeys, key) {
+			t.Fatalf("field %s is tagged json:%q, which #TranscodeInput in candy/plugin-media/schema does NOT declare — the projection has drifted from its source of truth", f.Name, key)
+		}
+		tagOf[key] = f.Name
+		switch f.Type.Kind() {
+		case reflect.String:
+			wire[key] = "probe"
+		case reflect.Bool:
+			wire[key] = true
+		case reflect.Int, reflect.Int64:
+			wire[key] = 7
+		case reflect.Float64:
+			wire[key] = 1.5
+		case reflect.Slice:
+			wire[key] = []any{"probe"}
+		case reflect.Map:
+			wire[key] = map[string]any{"k": "v"}
+		default:
+			// nested structs/pointers/interfaces are not filled by a flat wire map
+			continue
+		}
+	}
+	if exported == 0 {
+		t.Fatal("the projection has no exported fields — the test would prove nothing")
+	}
+
+	// Direction 2: SCHEMA -> STRUCT. Every key the schema declares must be carried by a field;
+	// a key the projection dropped is caught here, and it is checked against schemaKeys directly
+	// rather than against anything derived from the tags.
+	for _, key := range schemaKeys {
+		if _, ok := tagOf[key]; !ok {
+			t.Fatalf("schema key %q is declared by #TranscodeInput but NO exported field carries it — the projection is missing part of its schema", key)
+		}
+	}
+
+	b, err := json.Marshal(wire)
+	if err != nil {
+		t.Fatalf("marshal the wire map: %v", err)
+	}
+	// THE PATH: json -> struct, exactly `json.Unmarshal(req.GetParamsJson(), &op)`.
+	if err := json.Unmarshal(b, ptr.Interface()); err != nil {
+		t.Fatalf("decode the wire map into the projection: %v", err)
+	}
+	elem := ptr.Elem()
+	missing := []string{}
+	for key := range wire {
+		for i := 0; i < rt.NumField(); i++ {
+			f := rt.Field(i)
+			if f.PkgPath == "" && strings.Split(f.Tag.Get("json"), ",")[0] == key && elem.Field(i).IsZero() {
+				missing = append(missing, fmt.Sprintf("%s (field %s)", key, f.Name))
+			}
+		}
+	}
+	if len(missing) > 0 {
+		t.Fatalf("%d wire key(s) were not delivered into the projection: %v", len(missing), missing)
+	}
+	t.Logf("both directions hold: %d exported field(s), %d schema key(s), %d decoded", exported, len(schemaKeys), len(wire))
+}
+
+func contains(hay []string, needle string) bool {
+	for _, h := range hay {
+		if h == needle {
+			return true
+		}
+	}
+	return false
+}