Select checked implementations explicitly by target and ABI

src/execution-world/artifacts.ts

@@ -28,6 +28,35 @@ export interface PackageArtifacts {
   versions: ExecutionPlan["definition"]["versions"];
   implementations: ArtifactImplementation[];
 }
+export interface ImplementationSelection {
+  target: string;
+  compatibility: ArtifactImplementation["compatibility"];
+  /** Optional only when exactly one compatible implementation covers these exports. */
+  id?: string;
+  exports: readonly string[];
+}
+/** Select from a checked manifest; selection does not establish package trust or isolation.
+ * Never resolve ambiguity by manifest order or silently substitute a requested implementation.
+ */
+export function selectArtifactImplementation(
+  manifest: PackageArtifacts,
+  selection: ImplementationSelection,
+): ArtifactImplementation {
+  const candidates = manifest.implementations.filter(
+    (entry) =>
+      (selection.id === undefined || entry.id === selection.id) &&
+      entry.target === selection.target &&
+      entry.compatibility === selection.compatibility &&
+      selection.exports.every((id) => entry.exports.includes(id)),
+  );
+  if (candidates.length !== 1)
+    throw new ExecutionPlanError(
+      candidates.length ? "AMBIGUOUS_IMPLEMENTATION" : "IMPLEMENTATION_UNAVAILABLE",
+      manifest.packageRevisionId,
+      `${selection.id ?? "Select an explicit implementation ID"}: expected one ${selection.target}/${selection.compatibility} implementation covering the requested exports; found ${candidates.length}`,
+    );
+  return candidates[0]!;
+}
 export interface CheckedWorld {
   codec: "camino-world-v1";
   plan: string;