diff --git a/src/lib/auth.test.ts b/src/lib/auth.test.ts
new file mode 100644
index 0000000..d8bdf96
--- /dev/null
+++ b/src/lib/auth.test.ts
@@ -0,0 +1,22 @@
+import { test } from "node:test"
+import assert from "node:assert/strict"
+import { buildAuth } from "./auth.ts"
+
+test("no password -> no auth (open server)", () => {
+  assert.equal(buildAuth("opencode", undefined), undefined)
+  assert.equal(buildAuth("opencode", null), undefined)
+  assert.equal(buildAuth("opencode", ""), undefined)
+})
+
+test("password but no username -> defaults username to 'opencode' (Quick Connect fix)", () => {
+  // Regression guard: Quick Connect has no username field. Before the fix, an empty
+  // username made auth undefined and the app sent NO Authorization header -> 401.
+  assert.deepEqual(buildAuth(undefined, "secret"), { username: "opencode", password: "secret" })
+  assert.deepEqual(buildAuth("", "secret"), { username: "opencode", password: "secret" })
+  assert.deepEqual(buildAuth("   ", "secret"), { username: "opencode", password: "secret" })
+})
+
+test("explicit username preserved (Advanced mode), trimmed", () => {
+  assert.deepEqual(buildAuth("alice", "secret"), { username: "alice", password: "secret" })
+  assert.deepEqual(buildAuth("  alice  ", "secret"), { username: "alice", password: "secret" })
+})
diff --git a/src/lib/auth.ts b/src/lib/auth.ts
new file mode 100644
index 0000000..23da67c
--- /dev/null
+++ b/src/lib/auth.ts
@@ -0,0 +1,22 @@
+// Pure Basic-auth credential construction for opencode connections.
+// Extracted from stores/connections.ts so the username-defaulting rule is unit-testable
+// without pulling in zustand/expo (which have no resolver outside Metro).
+
+export interface BasicAuth {
+  username: string
+  password: string
+}
+
+// The opencode server's default Basic-auth username is "opencode"
+// (OPENCODE_SERVER_USERNAME ?? "opencode"). Quick Connect collects only a password
+// (it has no username field), so when a password is set but no username, default the
+// username to "opencode". Without this, an empty username made auth undefined entirely —
+// no Authorization header was sent — and a password-protected server returned 401,
+// i.e. the common "I set a password and now it won't connect" failure.
+export function buildAuth(
+  username: string | null | undefined,
+  password: string | null | undefined,
+): BasicAuth | undefined {
+  if (!password) return undefined
+  return { username: username?.trim() || "opencode", password }
+}
diff --git a/src/stores/connections.ts b/src/stores/connections.ts
index a96de05..a2700dd 100644
--- a/src/stores/connections.ts
+++ b/src/stores/connections.ts
@@ -4,6 +4,7 @@ import * as Crypto from "expo-crypto"
 import type { ServerConnection, ConnectionType } from "../lib/types"
 import { createClient, type Client, type Project } from "../lib/sdk"
 import { addBreadcrumb } from "../lib/sentry"
+import { buildAuth } from "../lib/auth"
 
 const CONNECTIONS_KEY = "opencode_connections"
 const PASSWORDS_PREFIX = "opencode_password_"
@@ -88,7 +89,7 @@ export const useConnections = create<ConnectionsState>((set, get) => ({
       let home: string | null = null
       if (active) {
         const password = await SecureStore.getItemAsync(`${PASSWORDS_PREFIX}${active.id}`)
-        const auth = active.username && password ? { username: active.username, password } : undefined
+        const auth = buildAuth(active.username, password)
         const built = buildClient(active.url, active.directory, auth)
         client = built.client
         base = built.base
@@ -147,7 +148,7 @@ export const useConnections = create<ConnectionsState>((set, get) => ({
 
     if (newConnection.active) {
       activeConnection = newConnection
-      const auth = newConnection.username && password ? { username: newConnection.username, password } : undefined
+      const auth = buildAuth(newConnection.username, password)
       const built = buildClient(newConnection.url, newConnection.directory, auth)
       client = built.client
       base = built.base
@@ -185,7 +186,7 @@ export const useConnections = create<ConnectionsState>((set, get) => ({
         newActive.active = true
         await SecureStore.setItemAsync(CONNECTIONS_KEY, JSON.stringify(connections))
         const password = await SecureStore.getItemAsync(`${PASSWORDS_PREFIX}${newActive.id}`)
-        const auth = newActive.username && password ? { username: newActive.username, password } : undefined
+        const auth = buildAuth(newActive.username, password)
         const built = buildClient(newActive.url, newActive.directory, auth)
         set({ connections, activeConnection: newActive, client: built.client, clientBase: built.base })
       } else {
@@ -212,7 +213,7 @@ export const useConnections = create<ConnectionsState>((set, get) => ({
 
     if (active) {
       const password = await SecureStore.getItemAsync(`${PASSWORDS_PREFIX}${active.id}`)
-      const auth = active.username && password ? { username: active.username, password } : undefined
+      const auth = buildAuth(active.username, password)
       const built = buildClient(active.url, active.directory, auth)
       client = built.client
       base = built.base
@@ -246,7 +247,7 @@ export const useConnections = create<ConnectionsState>((set, get) => ({
       const client = createClient({
         baseUrl: connection.url,
         directory: connection.directory,
-        auth: connection.username && password ? { username: connection.username, password } : undefined,
+        auth: buildAuth(connection.username, password),
       })
 
       await client.global.health()
@@ -265,7 +266,7 @@ export const useConnections = create<ConnectionsState>((set, get) => ({
     if (get().activeConnection?.id === id) {
       const active = connections.find((c) => c.id === id)!
       const password = await SecureStore.getItemAsync(`${PASSWORDS_PREFIX}${id}`)
-      const auth = active.username && password ? { username: active.username, password } : undefined
+      const auth = buildAuth(active.username, password)
       const built = buildClient(active.url, active.directory, auth)
       try {
         const [project, paths] = await Promise.all([