Implement independent presentation readiness boundaries

src/query/compile.ts

@@ -4,6 +4,8 @@ import {
   validate,
   specifiedRules,
   PossibleFragmentSpreadsRule,
+  NoUnusedVariablesRule,
+  GraphQLError,
   print,
   printSchema,
   visit,
@@ -201,10 +203,29 @@ export async function compileQuery(
       },
     }),
   );
+  const bindingVariables = new Set(
+    [...fragmentContracts.values()]
+      .filter((entry) => entry.mode === "reference")
+      .flatMap((entry) => Object.values(entry.variables)),
+  );
   const errors = validate(
     generated.schema,
     document,
-    specifiedRules.filter((rule) => rule !== PossibleFragmentSpreadsRule),
+    [
+      ...specifiedRules.filter((rule) => rule !== PossibleFragmentSpreadsRule && rule !== NoUnusedVariablesRule),
+      (context) => ({
+        OperationDefinition: {
+          leave(operation) {
+            const used = new Set(context.getRecursiveVariableUsages(operation).map(({ node }) => node.name.value));
+            for (const variable of operation.variableDefinitions ?? []) {
+              const name = variable.variable.name.value;
+              if (!used.has(name) && !bindingVariables.has(name))
+                context.reportError(new GraphQLError(`Variable "$${name}" is never used.`, { nodes: variable }));
+            }
+          },
+        },
+      }),
+    ],
     { maxErrors: 20 },
   );
   if (errors.length) {
@@ -399,6 +420,7 @@ export async function compileQuery(
         for (const selection of set.selections) {
           if (++expandedFields > 10000) fail("QUERY_WORK_LIMIT", "Expanded query exceeds 10000 fields", selection);
           if (selection.kind === "FragmentSpread") {
+            if (fragmentContracts.get(selection.name.value)?.mode === "reference") continue;
             add(
               fragments.get(selection.name.value)!.selectionSet,
               conditional || !!selection.directives?.length,
@@ -530,7 +552,9 @@ export async function compileQuery(
                 },
               ]
             : []),
-          ...selection(fragments.get(node.name.value)!.selectionSet, parent, inheritedConditions),
+          ...(contract?.mode === "reference"
+            ? []
+            : selection(fragments.get(node.name.value)!.selectionSet, parent, inheritedConditions)),
         ];
       }
       if (node.kind !== "Field") return [];
@@ -610,9 +634,10 @@ export async function compileQuery(
   const definitionDigest = createHash("sha256")
     .update(
       canonicalJson({
-        semantics: 4,
+        semantics: 5,
         declaration,
         normalized,
+        fragmentContracts: Object.fromEntries(fragmentContracts),
         // Source provenance belongs to the checked installation. Identical public
         // contracts keep their query identity when retained in another repository.
         // Closed generic identity remains explicit in revisionId/application.