refactor: isolate legacy flags

packages/server/test/auth.test.ts

@@ -0,0 +1,13 @@
+import { expect, test } from "bun:test"
+import { ServerAuth } from "@opencode-ai/server/auth"
+import { Option, Redacted } from "effect"
+
+test("accepts only the fixed opencode username", () => {
+  const config = { password: Option.some("secret") }
+  expect(ServerAuth.authorized({ username: "opencode", password: Redacted.make("secret") }, config)).toBe(true)
+  expect(ServerAuth.authorized({ username: "custom", password: Redacted.make("secret") }, config)).toBe(false)
+})
+
+test("encodes the fixed opencode username", () => {
+  expect(ServerAuth.header({ password: "secret" })).toBe(`Basic ${Buffer.from("opencode:secret").toString("base64")}`)
+})