fix: lire un document par la requête ancrée, readUnion ayant quitté le polyfill

Le contrat polyfill-surface passe de 1.0.0-dev.6 à 1.0.0-dev.15, épinglé
désormais sur le tag polyfill/v1.0.0-dev.15. readUnion et UnionSubject ont
été retirés en dev.8 : l'application e2e lit un document par un SELECT ancré
regroupé par sujet, en ignorant les registres urn:ng-eventually: que la
requête renvoie désormais.

La déclaration usage_ng-helpers retire ce que l'engagement a absorbé
(exemple de forme, initNg, orm_start_graph corrigé en dev.7, comportement
d'un document illisible, lecture d'un document public par sa seule
référence, pin par tag) et garde les demandes encore ouvertes.

contract_indexing-layer 4.0.1 (patch) : la lecture d'un index ne cite plus
readUnion.

e2e/run.ts

@@ -221,7 +221,7 @@ const { check, journey, finish } = declareSuite({
     {
       name: "The index answers an ordinary SPARQL query",
       checks: [
-        "readUnion returns both entries and the index's own declaration",
+        "reading the document returns both entries and the index's own declaration",
         "a SELECT for the entry predicate returns both entries, with their values",
         "a SELECT of the index's own subject returns the field it declares",
         "a stranger's SELECT returns the same entries",
@@ -278,7 +278,7 @@ function step<T>(what: string, ms: number, task: () => Promise<T>): Promise<T> {
  * to suit it.
  *
  * ── It reads the way an application reads ───────────────────────────────────
- * `read` is an ordinary `readUnion` of an ordinary document, or an anchored SELECT — the
+ * `read` is an ordinary anchored read of an ordinary document, or a narrower SELECT — the
  * only two ways anyone has of reading an index, the harness included. Nothing here reaches
  * for a way to hurry the layer below, because a consumer has none either.
  *
@@ -455,9 +455,9 @@ async function main(): Promise<void> {
         const declared = self?.props[INDEX_FIELD] ?? [];
         check(
           "the index document declares the field it indexes by",
-          declared.length === 1 && declared[0] === PUBLISHED_AT && self?.graph === index,
+          declared.length === 1 && declared[0] === PUBLISHED_AT,
           `subjects=${raw.length} self=${self === undefined ? "(not found)" : "found"} ` +
-            `graph=${self?.graph} declared=${JSON.stringify(declared)}`,
+            `declared=${JSON.stringify(declared)}`,
         );
       },
     });
@@ -762,8 +762,8 @@ async function main(): Promise<void> {
     // which is the state the question is about — one entry cannot tell a query that
     // returns everything from one that returns the first thing it finds.
     //
-    // WHAT IS BEING ASKED. This package documents one way of reading an index
-    // (`readUnion`) and issues no query of its own, so "an index is an ordinary document
+    // WHAT IS BEING ASKED. This package documents how to read an index and issues no
+    // query of its own, so "an index is an ordinary document
     // anyone queries normally" has never been anything but plausible. These four checks
     // are a measurement of that sentence, not a feature: an empty answer is a RESULT and
     // is reported as one, and a rejection is reported apart from it, because "the query
@@ -789,7 +789,7 @@ async function main(): Promise<void> {
           PUBLISHED_AT,
         );
         check(
-          "readUnion returns both entries and the index's own declaration",
+          "reading the document returns both entries and the index's own declaration",
           held.size === 2 && declares,
           `entries=${JSON.stringify([...held.keys()])} declares=${declares}`,
         );
@@ -826,7 +826,7 @@ async function main(): Promise<void> {
         );
 
         // The reader who matters: an index exists to be read by people who own neither it
-        // nor anything in it. `readUnion` already answers him (the journey above); whether
+        // nor anything in it. Reading the whole document already answers him (the journey above); whether
         // a query does is a separate question, and it is the one an application asks.
         const theirs = await step("Bob querying the index he does not own", BRIDGE_MS, () =>
           bob!.frame.evaluate(