Avoid rehashing validated Graph execution metadata during Candidate loading

src/execution-world/candidate.ts

@@ -130,7 +130,7 @@ export async function loadCheckedInstallationCandidate(
     const expectedGraph = graphExecutionRepresentation(plan, installation, kernel, queries);
     // The stored graph embeds the same kernel/query programs. Validate it in a
     // short-lived scope and retain the representation that shares those trees.
-    await (async () => {
+    const graphDigest = await (async () => {
       const input = await readJson(root, "graph-execution.json", scope);
       try {
         const digest = await hexDigestAsync(input.value);
@@ -140,6 +140,7 @@ export async function loadCheckedInstallationCandidate(
             root,
             "Stored graph execution differs from checked inputs",
           );
+        return digest;
       } finally {
         input.releaseTree();
       }
@@ -168,7 +169,8 @@ export async function loadCheckedInstallationCandidate(
     return {
       reference,
       workspace: plan.definition.workspace.workspaceId,
-      world: await hexDigestAsync(expectedGraph),
+      // The checked representation was already compared with this digest.
+      world: graphDigest,
       plan: kernel.plan as string,
       graphExecution: expectedGraph,
       provenance,