Let the merge preview and the provided manifest decode instead of judging (ADR 0578 §3)

Issue 1585, S12 (mesh-sdk half): buildstep's named paths and delivery.ProvidedManifest read with catalogue.Decode.

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

go/buildstep/trees.go

@@ -75,11 +75,12 @@ func ModuleTrees(ctx context.Context, run forgekey.Runner, env []string, dir, co
 }
 
 // narrow sets mt's Paths and its named Tree when the module's manifest names paths on every artifact (novox/hq ADR 0499
-// clause 2): one `git ls-tree -z` gives each named path's object at commit. The merge preview reads the manifest here, as
-// the indexer does, with catalogue.ParseManifestForInputs (issue 1751), and no other build step reads paths from one (ADR 0495 clause 1). A manifest that does not parse
-// is not narrowed: the indexer gives it none. A named path absent at commit fails, naming the module and the path.
+// clause 2): one `git ls-tree -z` gives each named path's object at commit. The merge preview decodes the manifest here
+// (catalogue.Decode: a build step judges no manifest, novox/hq ADR 0578 §3), and no other build step reads paths from one
+// (ADR 0495 clause 1). A manifest that does not decode is not narrowed: the indexer gives it none. A named path absent at
+// commit fails, naming the module and the path.
 func narrow(ctx context.Context, run forgekey.Runner, env []string, dir, commit, mdir string, raw []byte, mt *ModuleTree) error {
-	m, err := catalogue.ParseManifestForInputs(raw)
+	m, err := catalogue.Decode(raw)
 	if err != nil {
 		return nil
 	}

go/delivery/provided.go

@@ -29,9 +29,10 @@ func ProvidedManifest(module string) (catalogue.Manifest, []byte, error) {
 	if err != nil {
 		return catalogue.Manifest{}, nil, err
 	}
-	m, err := catalogue.ParseManifestForInputs(raw)
+	// Decoded as every reader decodes a manifest (novox/hq ADR 0578 §3); its judgement is the indexer's.
+	m, err := catalogue.Decode(raw)
 	if err != nil {
-		return catalogue.Manifest{}, raw, fmt.Errorf("delivery: the manifest mesh-sdk provides for %s is refused by its own reader: %w", module, err)
+		return catalogue.Manifest{}, raw, fmt.Errorf("delivery: the manifest mesh-sdk provides for %s does not decode: %w", module, err)
 	}
 	return m, raw, nil
 }