diff --git a/docs/database-backends.md b/docs/database-backends.md
index fbf5ff5a..0fdd4753 100644
--- a/docs/database-backends.md
+++ b/docs/database-backends.md
@@ -189,6 +189,19 @@ Tested against PostgreSQL 16 and MySQL 8. **MariaDB is not a substitute for
 MySQL when testing** — it accepts DDL that MySQL 8 rejects, which has hidden a
 real defect here more than once.
 
+### What neither of them covers
+
+Both harnesses build a `DatabaseContext` of their own, so neither runs
+`createCurrentRepositoryContext()` — the one the application actually uses.
+That gap hid a hardcoded `dialect: "sqlite"` in it: every engine reported
+itself as SQLite at runtime while all three test passes stayed green, which on
+MySQL meant `upsert` reached for `onConflictDoUpdate` and died with a
+TypeError on the first write.
+
+Anything the factory decides from the dialect needs its own test against the
+factory. Asserting it through a hand-built context proves nothing about what
+runs in production.
+
 ## Known limits
 
 - The desktop app always uses SQLite. It embeds its own backend and cannot ship
diff --git a/src/backend/database/repositories/factory.ts b/src/backend/database/repositories/factory.ts
index 12eaee51..9600f439 100644
--- a/src/backend/database/repositories/factory.ts
+++ b/src/backend/database/repositories/factory.ts
@@ -47,9 +47,21 @@ import { UserRepository } from "./user-repository.js";
 import { VaultProfileRepository } from "./vault-profile-repository.js";
 import { VaultTokenRepository } from "./vault-token-repository.js";
 
+/**
+ * The context every repository runs against.
+ *
+ * The dialect has to be resolved, not assumed: it is what `returning.ts` reads
+ * to decide whether it can ask for RETURNING, and whether an upsert spells
+ * itself `onConflictDoUpdate` or `onDuplicateKeyUpdate`. Reporting "sqlite"
+ * while connected to MySQL makes the second of those a TypeError on the first
+ * write.
+ *
+ * Both cross-dialect harnesses build a DatabaseContext themselves, so neither
+ * exercises this function — see tests/database/repositories/factory-context.
+ */
 export function createCurrentRepositoryContext(): DatabaseContext {
   return {
-    dialect: "sqlite",
+    dialect: resolveDatabaseDialect(),
     drizzle: getDb(),
   };
 }
diff --git a/src/backend/tests/database/repositories/factory-context.test.ts b/src/backend/tests/database/repositories/factory-context.test.ts
new file mode 100644
index 00000000..5f9fe8d8
--- /dev/null
+++ b/src/backend/tests/database/repositories/factory-context.test.ts
@@ -0,0 +1,66 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { DATABASE_DIALECT_ENV } from "../../../database/db/dialect.js";
+
+// getDb() throws unless a database was initialized; the context's handle is
+// not what this file is about.
+vi.mock("../../../database/db/index.js", () => ({
+  getDb: () => ({}),
+  getSqlite: () => ({}),
+  DatabaseSaveTrigger: { forceSave: vi.fn() },
+}));
+
+const { createCurrentRepositoryContext, createCurrentRepositoryWriteHook } =
+  await import("../../../database/repositories/factory.js");
+
+// Neither cross-dialect harness reaches this function: both
+// tests/database/repositories/test-support.ts and scripts/verify-dialects.mjs
+// construct a DatabaseContext of their own. That is why the production path
+// could report "sqlite" while connected to MySQL with CI green on all three
+// engines, and why this asserts on the real factory rather than a fixture.
+describe("createCurrentRepositoryContext", () => {
+  const saved = process.env[DATABASE_DIALECT_ENV];
+
+  beforeEach(() => {
+    delete process.env[DATABASE_DIALECT_ENV];
+  });
+
+  afterEach(() => {
+    if (saved === undefined) delete process.env[DATABASE_DIALECT_ENV];
+    else process.env[DATABASE_DIALECT_ENV] = saved;
+  });
+
+  it("defaults to sqlite when nothing is configured", () => {
+    expect(createCurrentRepositoryContext().dialect).toBe("sqlite");
+  });
+
+  it("reports the configured dialect", () => {
+    for (const dialect of ["sqlite", "postgres", "mysql"]) {
+      process.env[DATABASE_DIALECT_ENV] = dialect;
+      expect(createCurrentRepositoryContext().dialect).toBe(dialect);
+    }
+  });
+
+  it("rejects an unsupported dialect rather than falling back to sqlite", () => {
+    process.env[DATABASE_DIALECT_ENV] = "oracle";
+    expect(() => createCurrentRepositoryContext()).toThrow(/oracle/);
+  });
+});
+
+describe("createCurrentRepositoryWriteHook", () => {
+  const saved = process.env[DATABASE_DIALECT_ENV];
+
+  afterEach(() => {
+    if (saved === undefined) delete process.env[DATABASE_DIALECT_ENV];
+    else process.env[DATABASE_DIALECT_ENV] = saved;
+  });
+
+  it("installs a persist hook only for sqlite", () => {
+    process.env[DATABASE_DIALECT_ENV] = "sqlite";
+    expect(createCurrentRepositoryWriteHook("test")).toBeTypeOf("function");
+
+    for (const dialect of ["postgres", "mysql"]) {
+      process.env[DATABASE_DIALECT_ENV] = dialect;
+      expect(createCurrentRepositoryWriteHook("test")).toBeUndefined();
+    }
+  });
+});