diff --git a/packages/client/src/access-log.ts b/packages/client/src/access-log.ts
new file mode 100644
index 0000000..8da8b5b
--- /dev/null
+++ b/packages/client/src/access-log.ts
@@ -0,0 +1,81 @@
+/**
+ * access-log — an OFF-by-default observability probe for document access.
+ *
+ * Diagnostic tool for the shared-wallet isolation footgun: on ONE physical
+ * wallet, several virtual identities coexist, and a read must never surface a
+ * document scoped to another identity. When it does (identity B reading identity
+ * A's doc), the leak is invisible in the data — it looks like a normal read. This
+ * probe makes it VISIBLE: every real read/write is logged, prefixed by the ACTIVE
+ * identity (the discriminating virtual identity, NOT the constant physical wallet
+ * id), so replaying the scenario shows the exact line where a doc is accessed
+ * under the wrong identity.
+ *
+ * OFF by default → zero overhead, zero output. Turned on either by the SDK config
+ * option `debugAccessLog: true` (via {@link setAccessLog}) or, without touching
+ * the calling code, by the env var `NG_EVENTUALLY_ACCESS_LOG=1`. The `enabled()`
+ * gate is a single boolean read on the hot path when off.
+ *
+ * Polyfill-era, like the rest of /polyfill; removed at the real multi-store
+ * migration where the broker/verifier enforces isolation natively.
+ */
+
+import { getCurrentUser } from "./polyfill";
+
+/** Access kind: a document READ or a document WRITE. */
+export type AccessOp = "READ" | "WRITE";
+
+// Config-driven toggle (set by configure() via setAccessLog); default OFF.
+let configEnabled = false;
+
+/**
+ * Env override: `NG_EVENTUALLY_ACCESS_LOG=1` (or `true`) turns the log on without
+ * a code change in the caller. Read once, tolerant of env access throwing (e.g.
+ * a locked-down runtime), so it never breaks the hot path.
+ */
+function envEnabled(): boolean {
+  try {
+    const v = (globalThis as any)?.process?.env?.NG_EVENTUALLY_ACCESS_LOG;
+    return v === "1" || v === "true";
+  } catch {
+    return false;
+  }
+}
+
+/** Set the config-driven toggle (called from configure()). */
+export function setAccessLog(on: boolean): void {
+  configEnabled = on;
+}
+
+/** Whether access logging is currently on (config OR env). */
+export function enabled(): boolean {
+  return configEnabled || envEnabled();
+}
+
+/**
+ * The identity to prefix an access line with: the ACTIVE virtual identity
+ * (`getCurrentUser`) — the account/space the operation is scoped under, which is
+ * the discriminating signal for the isolation leak. NOT the physical wallet id
+ * (shared, constant → useless). `(none)` when no identity is set yet (startup).
+ */
+function activeIdentity(): string {
+  return getCurrentUser() ?? "(none)";
+}
+
+/**
+ * Log one document access — but ONLY when {@link enabled}. Off → returns
+ * immediately, prints nothing. Format:
+ *   `[<identity>] READ <nuri> (<label>)` — optionally with `<extra>` appended
+ * (e.g. ` → 3 rows`, a strong signal a doc rendered data under an identity that
+ * should see nothing).
+ */
+export function logAccess(
+  op: AccessOp,
+  nuri: string,
+  label: string,
+  extra?: string,
+): void {
+  if (!enabled()) return;
+  console.log(
+    "[" + activeIdentity() + "] " + op + " " + nuri + " (" + label + ")" + (extra ?? ""),
+  );
+}
diff --git a/packages/client/src/docs.ts b/packages/client/src/docs.ts
index 026354b..b51b5b5 100644
--- a/packages/client/src/docs.ts
+++ b/packages/client/src/docs.ts
@@ -14,8 +14,26 @@
  */
 
 import { getConfig } from "./polyfill";
+import { logAccess, enabled as accessLogEnabled } from "./access-log";
 import type { Nuri } from "./types";
 
+// The low common point for ALL document access: every read in the SDK routes
+// through `sparqlQuery`, every write through `sparqlUpdate` (+ container creation
+// through `docCreate`) — each ultimately calling the real injected `ng` here. The
+// access log is therefore instrumented HERE so no access path escapes it. Callers
+// pass a semantic `label` (readDoc|readUnion|listMyEntityDocs|writeEntity|deposit
+// |…); it is a lib-internal probe param, NOT forwarded to the real `ng` (the docs
+// primitives forward the exact SDK signature — see test/docs.test.ts). When the
+// log is OFF (default) the extra param is inert and costs one boolean read.
+
+/** Count rows in a raw SPARQL SELECT result, tolerant of the possible shapes. */
+function rowCount(result: unknown): number {
+  if (!result) return 0;
+  if (Array.isArray(result)) return result.length;
+  const anyRes = result as { results?: { bindings?: unknown[] } };
+  return anyRes.results?.bindings?.length ?? 0;
+}
+
 /**
  * Create one document → its NURI.
  *
@@ -31,7 +49,10 @@ export async function docCreate(
   store?: unknown,
 ): Promise<Nuri> {
   const { ng } = getConfig();
-  return ng.doc_create(sessionId, crdt, cls, dest, store);
+  const nuri = await ng.doc_create(sessionId, crdt, cls, dest, store);
+  // A container creation is a WRITE; the NURI only exists after the call.
+  logAccess("WRITE", nuri, "docCreate");
+  return nuri;
 }
 
 /**
@@ -44,8 +65,11 @@ export async function sparqlUpdate(
   sessionId: string,
   query: string,
   anchor?: Nuri,
+  label = "sparqlUpdate",
 ): Promise<void> {
   const { ng } = getConfig();
+  // `label` is a lib-internal access-log tag, NOT forwarded to `ng`.
+  logAccess("WRITE", anchor ?? "(no anchor)", label);
   return ng.sparql_update(sessionId, query, anchor);
 }
 
@@ -60,7 +84,16 @@ export async function sparqlQuery(
   query: string,
   base?: string,
   anchor?: Nuri,
+  label = "sparqlQuery",
 ): Promise<unknown> {
   const { ng } = getConfig();
-  return ng.sparql_query(sessionId, query, base, anchor);
+  // `label` is a lib-internal access-log tag, NOT forwarded to `ng`.
+  const result = await ng.sparql_query(sessionId, query, base, anchor);
+  // Log AFTER the read so the row count (a strong leak signal: a doc rendering
+  // rows under an identity that should see nothing) can be appended. Skip the
+  // rowCount work entirely when the log is off.
+  if (accessLogEnabled()) {
+    logAccess("READ", anchor ?? "(no anchor)", label, " → " + rowCount(result) + " rows");
+  }
+  return result;
 }
diff --git a/packages/client/src/inbox.ts b/packages/client/src/inbox.ts
index 8209272..863fb8f 100644
--- a/packages/client/src/inbox.ts
+++ b/packages/client/src/inbox.ts
@@ -142,7 +142,7 @@ export async function post(targetInbox: Nuri, opts: PostOptions): Promise<void>
         <${P.payload}> "${payloadLiteral}" ;
         <${P.ts}> "${ts}"${fromTriple} .
     }`;
-  await sparqlUpdate(sid, update, targetInbox);
+  await sparqlUpdate(sid, update, targetInbox, "deposit");
 }
 
 // --- read --------------------------------------------------------------
@@ -166,7 +166,7 @@ export async function read(targetInbox: Nuri): Promise<Deposit[]> {
          <${P.ts}> ?ts .
       OPTIONAL { ?d <${P.from}> ?from }
     }`;
-  const result = await sparqlQuery(sid, query, undefined, targetInbox);
+  const result = await sparqlQuery(sid, query, undefined, targetInbox, "inboxRead");
   const deposits: Deposit[] = [];
   for (const row of readBindings(result)) {
     const rawPayload = row.payload?.value ?? "null";
diff --git a/packages/client/src/polyfill.ts b/packages/client/src/polyfill.ts
index 6147854..61284d7 100644
--- a/packages/client/src/polyfill.ts
+++ b/packages/client/src/polyfill.ts
@@ -11,6 +11,7 @@
 import type { NgLike, UseShapeLike, PrincipalId } from "./types";
 import type { RegistrySession } from "./store-registry";
 import { CapRegistry } from "./caps";
+import { setAccessLog } from "./access-log";
 
 /**
  * Consumer-injected dependencies of the storeRegistry (polyfill-era). The
@@ -34,6 +35,13 @@ export interface EventuallyConfig {
   sharedWallet?: { name: string; secret: string };
   /** Initial current user; may also be set later via {@link setCurrentUser}. */
   currentUser?: PrincipalId;
+  /**
+   * Turn on the OFF-by-default document access log (see {@link ./access-log}):
+   * every real read/write is printed, prefixed by the active identity, to
+   * diagnose the shared-wallet isolation leak. Also enablable without a code
+   * change via the env var `NG_EVENTUALLY_ACCESS_LOG=1`. Default: false.
+   */
+  debugAccessLog?: boolean;
   /** REAL `@ng-org/web` `init` (lifecycle) — forwarded by the lib's `init()`. */
   init?: (...args: any[]) => any;
   /** REAL `@ng-org/orm` `initNg` (ORM signals) — forwarded by the lib's `initNg()`. */
@@ -50,6 +58,7 @@ let caps = new CapRegistry();
 export function configure(c: EventuallyConfig): void {
   cfg = c;
   currentUser = c.currentUser ?? null;
+  setAccessLog(c.debugAccessLog ?? false);
 }
 
 /** @internal — used by the SDK-shaped wrappers to reach the injected real SDK. */
diff --git a/packages/client/src/read-model.ts b/packages/client/src/read-model.ts
index 723e0cb..cf83af1 100644
--- a/packages/client/src/read-model.ts
+++ b/packages/client/src/read-model.ts
@@ -111,6 +111,7 @@ async function readDoc(
       "SELECT ?s ?p ?o WHERE { ?s ?p ?o }",
       undefined,
       nuri,
+      "readDoc",
     );
     return bindings(res);
   } catch (error) {
diff --git a/packages/client/src/store-registry.ts b/packages/client/src/store-registry.ts
index 0840405..10b1b0e 100644
--- a/packages/client/src/store-registry.ts
+++ b/packages/client/src/store-registry.ts
@@ -185,7 +185,7 @@ export async function loadShim(): Promise<Map<string, AccountRecord>> {
     }`;
   const map = new Map<string, AccountRecord>();
   try {
-    const result = await sparqlQuery(s.sessionId, query, undefined, anchor);
+    const result = await sparqlQuery(s.sessionId, query, undefined, anchor, "loadShim");
     for (const row of readBindings(result)) {
       const id = bindingValue(row, "id");
       if (!id) continue;
@@ -238,7 +238,7 @@ export async function resolveAccount(id: string): Promise<AccountRecord | null>
       }
     }`;
   try {
-    const result = await sparqlQuery(s.sessionId, query, undefined, anchor);
+    const result = await sparqlQuery(s.sessionId, query, undefined, anchor, "resolveAccount");
     const rows = readBindings(result);
     if (rows.length === 0) return null;
     const row = rows[0]!;
@@ -305,7 +305,7 @@ export async function ensureAccount(id: string): Promise<AccountRecord> {
       }
     }`;
   try {
-    await sparqlUpdate(s.sessionId, update, anchor);
+    await sparqlUpdate(s.sessionId, update, anchor, "ensureAccount");
   } catch (error) {
     console.error("[storeRegistry] ensureAccount persist failed:", error);
   }
@@ -432,6 +432,7 @@ export async function createEntityDoc(id: string, scope: Scope): Promise<Nuri> {
       // a literal → escapeLiteral.
       `INSERT DATA { <${INDEX_SUBJECT}> <${P.contains}> "${escapeLiteral(entityNuri)}" }`,
       indexDoc,
+      "createEntityDoc",
     );
   } catch (error) {
     console.error("[storeRegistry] createEntityDoc index append failed:", error);
@@ -451,6 +452,7 @@ async function readScopeIndex(indexDoc: Nuri): Promise<Nuri[]> {
       `SELECT ?e WHERE { <${INDEX_SUBJECT}> <${P.contains}> ?e }`,
       undefined,
       indexDoc,
+      "readScopeIndex",
     );
     for (const row of readBindings(res)) {
       const v = bindingValue(row, "e");