fix(authz): guard scopeKey's tenantId type, add deterministic C1/C2 guard

N1: scopeKey guarded the empty-string VALUE but not the TYPE. A
non-string tenantId (null, 0, false, an object) flowed through
un-normalised, and the adapters disagreed about the result - db
rejects null on NOT NULL, memory accepts it as an unreachable row; 0
and false stringify differently and could collide. Now
`typeof tenantId !== "string" || tenantId === ""` is refused with the
same WRN-AUTHZ-SCOPE error. Added a conformance case covering
null/0/false/{}.

N2: nothing failed if grant() were re-wrapped in db.tx, reintroducing
the shared-connection rollback from C1/C2 - timing-based tests can't
reliably prove a transaction is never opened. Added
db-no-transaction.test.ts: a fake Db with a spied driver.transaction
and statement-recording all/exec, driving every PermissionStore method
and asserting zero transaction calls and no "BEGIN" in any recorded
statement. Verified it fails when grant() is temporarily re-wrapped in
db.tx, then restored.

Also documents two things in db.ts as comments only: the UNIQUE
constraints are now load-bearing for ON CONFLICT/ON DUPLICATE KEY
target inference, and MySQL's VALUES(effect) upsert syntax is
deprecated since 8.0.20 (no MySQL server in CI to catch its removal).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/authz/test/db-no-transaction.test.ts

@@ -0,0 +1,85 @@
+import { describe, expect, test } from "bun:test";
+import type { Db, Dialect, Driver, ExecResult, Row, TxHandle } from "@wrnexus/db";
+import { dbPermissionStore } from "../src/db.ts";
+
+/**
+ * A deterministic regression guard for C1/C2 (round-1 review): grant() used to
+ * wrap its delete-then-insert in db.tx, and the sqlite driver runs a bare
+ * BEGIN on one shared, unserialized connection - so an open transaction there
+ * could sweep in and discard a concurrent bare write from another method.
+ * Timing-based tests can't reliably prove the absence of that; this can,
+ * because it needs no concurrency at all - it just asserts the store never
+ * asks the driver to open a transaction in the first place.
+ */
+function makeFakeDb(): { db: Db; statements: string[]; transactionCalls: number } {
+  const statements: string[] = [];
+  const stats = { transactionCalls: 0 };
+
+  const driver: Driver = {
+    dialect: "sqlite" as Dialect,
+    async query(sql: string): Promise<Row[]> {
+      statements.push(sql);
+      return [];
+    },
+    async exec(sql: string): Promise<ExecResult> {
+      statements.push(sql);
+      return { changes: 0 };
+    },
+    async transaction<T>(fn: (tx: TxHandle) => Promise<T>): Promise<T> {
+      // The spy: this must never be called by a transaction-free store.
+      stats.transactionCalls++;
+      statements.push("BEGIN");
+      return fn(driver);
+    },
+    close() {},
+  };
+
+  const db: Db = {
+    driver,
+    async all<T = Row>(sql: string): Promise<T[]> {
+      statements.push(sql);
+      return [];
+    },
+    async one<T = Row>(sql: string): Promise<T | null> {
+      statements.push(sql);
+      return null;
+    },
+    async exec(sql: string): Promise<ExecResult> {
+      statements.push(sql);
+      return { changes: 0 };
+    },
+    async tx<T>(fn: (tx: Db) => Promise<T>): Promise<T> {
+      // Routed through the same driver.transaction spy a real Db would use.
+      return driver.transaction(() => fn(db));
+    },
+    async createTable() {},
+    close() {},
+  };
+
+  return {
+    db,
+    statements,
+    get transactionCalls() {
+      return stats.transactionCalls;
+    },
+  };
+}
+
+describe("dbPermissionStore opens no transaction", () => {
+  test("the store opens no transaction: a shared-connection rollback would discard concurrent writes from other methods", async () => {
+    const fake = makeFakeDb();
+    const store = dbPermissionStore(fake.db);
+
+    await store.assignmentsFor("u1");
+    await store.assignRole("u1", "editor");
+    await store.revokeRole("u1", "editor");
+    await store.grant("u1", "post:write", "allow");
+    await store.revokeGrant("u1", "post:write");
+    await store.listSubjects();
+
+    expect(fake.transactionCalls).toBe(0);
+    for (const sql of fake.statements) {
+      expect(sql).not.toContain("BEGIN");
+    }
+  });
+});

packages/authz/test/store-conformance.ts

@@ -136,6 +136,15 @@ export function runStoreConformance(name: string, makeStore: () => Promise<Permi
       await expect(store.assignRole("g1", "admin", { tenantId: "" })).rejects.toThrow(/tenantId/);
     });
 
+    test("a non-string tenantId is refused", async () => {
+      // Same class as the empty-string case: the caller controls this value.
+      for (const bad of [null, 0, false, {}]) {
+        await expect(store.assignmentsFor("u1", { tenantId: bad as never })).rejects.toThrow(
+          /tenantId/,
+        );
+      }
+    });
+
     test("concurrent identical assignRole calls all resolve", async () => {
       // Check-then-act loses this race; the UNIQUE constraint then rejects
       // every loser even though the desired end state was already reached.