Load checked installations independently of the running compiler (WI-16)

Keep compiler-dependent checks in Nix builds; load stored plans and programs with original provenance and runtime artifact validation. Allow an identical executable world to receive a new activation epoch after a toolchain rebuild.

Compiler-update/altered-program regression, coordinator and full sandboxed integration checks pass; lint and formatting pass. Default platform/source wiring remains the next task.

src/execution-world/installation.ts

@@ -1,6 +1,6 @@
 import path from "node:path";
 import { loadCheckedArtifactWorld } from "./receipts.js";
-import { contentArtifactUrl } from "./files.js";
+import { contentArtifactUrl, loadArtifactWorld, type LoadedArtifactWorld } from "./files.js";
 import { selectArtifactImplementation, type ArtifactImplementation, type ComponentArtifact } from "./artifacts.js";
 import { ExecutionPlanError, hexDigest, type ExecutionPlan } from "./plan.js";
 import {
@@ -108,15 +108,32 @@ export interface InstalledComponent {
   readonly compatibility: ComponentArtifact["compatibility"];
   readonly sharedModules: Readonly<Record<keyof ComponentArtifact["sharedModules"], string>>;
 }
-/** Verify candidate receipts before assembling process entrypoints and browser assets.
- * This grants no authority to activate a world or run optional modules in process. */
-export async function loadExecutionInstallation(
+/** Build-time validation uses the compiler selected by the Nix derivation. */
+export async function checkExecutionInstallation(
   plan: ExecutionPlan,
   roots: Readonly<Record<string, string>>,
   generator: string,
   selections: Readonly<Record<string, PackageInstallationSelection>> = {},
 ): Promise<ExecutionInstallation> {
   const loaded = await loadCheckedArtifactWorld(plan, roots, generator);
+  return assembleExecutionInstallation(plan, roots, loaded, selections);
+}
+/** Load immutable artifacts without regenerating bindings with the host compiler.
+ * Format, coverage, content and runtime ABI checks still apply. This grants no
+ * authority to activate a world or run optional modules in process. */
+export async function loadExecutionInstallation(
+  plan: ExecutionPlan,
+  roots: Readonly<Record<string, string>>,
+  selections: Readonly<Record<string, PackageInstallationSelection>> = {},
+): Promise<ExecutionInstallation> {
+  return assembleExecutionInstallation(plan, roots, await loadArtifactWorld(plan, roots), selections);
+}
+function assembleExecutionInstallation(
+  plan: ExecutionPlan,
+  roots: Readonly<Record<string, string>>,
+  loaded: LoadedArtifactWorld,
+  selections: Readonly<Record<string, PackageInstallationSelection>>,
+): ExecutionInstallation {
   const fail = (where: string, message: string): never => {
     throw new ExecutionPlanError("INSTALLATION_INVALID", where, message);
   };