fix(client): anchored default-graph writes for inbox + scope index

Inbox deposits and the per-(account,scope) index append were written into an
explicit GRAPH <plainNuri> named graph, which the real broker stores separately
from the repo's default graph (repo_graph_name with overlay suffix) — so an
anchored default-graph read (read-model.readDoc) never saw them and deposits
did not round-trip. Drop the GRAPH wrapper: the anchor scopes the write to the
repo's default graph, matching the read. Mocks updated accordingly.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/client/test/store-registry.test.ts

@@ -72,10 +72,26 @@ function makeFakeNg() {
   // injection escaping keeps the query well-formed.
   const sparql_update = mock(async (...a: unknown[]) => {
     const query = a[1] as string;
+    const anchor = a[2] as string | undefined;
+    // TWO shapes coexist here:
+    //  - the shim account write STILL uses `GRAPH <${privateStore}>` — the
+    //    private STORE repo's graph name equals the plain store NURI, so it
+    //    round-trips (login must not regress). Key it by that GRAPH IRI.
+    //  - the per-entity INDEX write has NO explicit GRAPH — the real broker keys
+    //    it by the ANCHORED repo's default graph (repo_graph_name(id, overlay)),
+    //    so key it by the ANCHOR arg (a[2]). An explicit `GRAPH <indexDoc>`
+    //    would target a phantom graph → must NOT round-trip.
     const gm = query.match(/GRAPH <([^>]+)>\s*\{([\s\S]*)\}/);
-    if (!gm) return undefined;
-    const g = gm[1]!;
-    const body = gm[2]!;
+    let g: string;
+    let body: string;
+    if (gm) {
+      g = gm[1]!;
+      body = gm[2]!;
+    } else {
+      if (!anchor) return undefined;
+      g = anchor;
+      body = query.replace(/^\s*INSERT DATA\s*\{/, "").replace(/\}\s*$/, "");
+    }
     // Subject is the first <...> token in the body.
     const sm = body.match(/<([^>]+)>/);
     if (!sm) return undefined;