feat!: retirer readUnion de la surface publiee, et lire un document par requete ancree

readUnion etait N requetes ancrees plus une politique de lot : une lecture
qui echoue avalee en reponse vide, un document dont on ne detient pas la cle
ecarte au lieu d'etre refuse, un regroupement en sacs de proprietes, et le
filtrage du prefixe reserve. Rien en amont ne repond a cette composition, et
son annotation citait sparql_query -- une citation exacte attachee a une
affirmation fausse. Une composition ne s'aligne pas sur une fonction.

Ce qui reste est ce qu'il y avait dessous : docs.sparqlQuery ancre sur un
document, qui va deja chercher la cle servie par le magasin public -- donc
une reference nue suffit toujours pour lire un document public, sans rien
changer a useShapeQuery. Lire plusieurs documents, c'est cet appel une fois
par document, et la tolerance a une lecture qui echoue revient a l'appelant,
la ou l'amont la laisse : une requete ancree sur un depot que le verifier ne
detient pas rejette.

Cote src, l'unique lecture interne restante devient read-document.ts : un
document, une requete ancree, precedee de l'ouverture du depot -- barriere
que index-deposit consulte pour distinguer une absence d'un depot non
synchronise. Le harnais e2e et l'exemple composent la leur, avec leur catch
visible au point d'appel.

Version majeure : 1.0.0-dev.8.

packages/polyfill/test/inbox-dispatch.test.ts

@@ -41,7 +41,7 @@ import { resetOpenedRepos, setOpenTimeoutForTests } from "../src/emulated-verifi
 import { resetPublicStoreFetches } from "../src/emulated-verifier/public-store";
 import { ENTRY_VALUE, INDEX_FIELD } from "../src/emulated-verifier/index-deposit";
 import { postToDocument } from "../src/surface/inbox";
-import { readUnion } from "../src/surface/read-model";
+import { readDocumentSubjects } from "../src/surface/read-document";
 import { sparqlUpdate } from "../src/surface/docs";
 import type { Nuri } from "../src/model/types";
 
@@ -261,7 +261,7 @@ async function write(doc: Nuri, p: string, o: string): Promise<void> {
 
 /** Every value the index holds for `object` — one per entry written. */
 async function entryValuesFor(index: Nuri, object: Nuri): Promise<string[]> {
-  const subjects = await readUnion([index]);
+  const subjects = await readDocumentSubjects(index);
   return subjects.filter((s) => s.subject === object).flatMap((s) => s.props[ENTRY_VALUE] ?? []);
 }
 
@@ -340,9 +340,10 @@ test("a reference nobody can resolve is reported, and costs the index nothing",
   await bobSignsInOnce();
   const { index, object } = await aliceOpensAnIndex([WHEN]);
 
-  // A reference this holder cannot even attempt — no cap, so `readUnion` drops it before
-  // issuing a query — and a resolvable one BEHIND it, which is what makes the question
-  // answerable at all.
+  // A reference this holder cannot reach — no cap, so the anchored read REFUSES it (until
+  // `1.0.0-dev.8` `readUnion` dropped it before issuing a query, which reached this arm as
+  // an empty answer instead of a failure) — and a resolvable one BEHIND it, which is what
+  // makes the question answerable at all.
   await bobDepositsInto(index, "did:ng:o:nowhere", 1);
   await bobDepositsInto(index, object, 2);
 
@@ -560,9 +561,9 @@ test("an EMPTY but readable object is absent — reported, and the queue behind
 
   // A document Alice really holds and that really reads — it just has no triples. This is
   // the genuine clean-empty read, and until 2026-08-26 NOTHING exercised it: the only test
-  // of this branch pointed at `did:ng:o:nowhere`, which `readUnion`'s possession gate drops
-  // before any query is issued. So the branch that decides "absent vs unreadable" on a real
-  // read was uncovered, which is how two opposite misclassifications shipped through it.
+  // of this branch pointed at `did:ng:o:nowhere`, which the possession gate refuses before
+  // any rows exist. So the branch that decides "absent vs unreadable" on a real read was
+  // uncovered, which is how two opposite misclassifications shipped through it.
   setCurrentUser("alice");
   const empty = await createEntityDoc("alice", "public");
   setCurrentUser(null);