diff --git a/Cargo.lock b/Cargo.lock
index 45fe80387..330771d91 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3168,6 +3168,13 @@ dependencies = [
  "serde_json",
 ]
 
+[[package]]
+name = "op-auth-bridge"
+version = "0.8.2"
+dependencies = [
+ "serde_json",
+]
+
 [[package]]
 name = "op-cli"
 version = "0.8.2"
@@ -3315,6 +3322,7 @@ dependencies = [
  "op-acp",
  "op-ai",
  "op-ai-skills",
+ "op-auth-bridge",
  "op-codegen",
  "op-config-store",
  "op-design-lint",
@@ -3358,6 +3366,7 @@ dependencies = [
  "jian-skia",
  "khronos-egl",
  "libloading",
+ "op-auth-bridge",
  "op-editor-core",
  "op-editor-ui",
  "op-i18n",
diff --git a/crates/op-auth-bridge/Cargo.toml b/crates/op-auth-bridge/Cargo.toml
new file mode 100644
index 000000000..e2a092914
--- /dev/null
+++ b/crates/op-auth-bridge/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "op-auth-bridge"
+description = "Thin bridge to the proprietary op-auth static library, with a stub fallback"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+authors.workspace = true
+repository.workspace = true
+
+[dependencies]
+serde_json = { workspace = true }
diff --git a/crates/op-auth-bridge/build.rs b/crates/op-auth-bridge/build.rs
new file mode 100644
index 000000000..1ad8015b7
--- /dev/null
+++ b/crates/op-auth-bridge/build.rs
@@ -0,0 +1,33 @@
+//! Link the prebuilt proprietary auth library when one exists for the
+//! current target; otherwise the crate compiles its stub and the account
+//! UI stays hidden. Open-source checkouts therefore always build.
+
+use std::env;
+use std::path::PathBuf;
+
+fn main() {
+    println!("cargo:rustc-check-cfg=cfg(op_auth_prebuilt)");
+    println!("cargo:rerun-if-changed=prebuilt");
+
+    let target = env::var("TARGET").unwrap_or_default();
+    let manifest_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap());
+    let prebuilt_dir = manifest_dir.join("prebuilt").join(&target);
+    if !prebuilt_dir.join("libop_auth.a").is_file() {
+        return;
+    }
+
+    println!("cargo:rustc-cfg=op_auth_prebuilt");
+    println!("cargo:rustc-link-search=native={}", prebuilt_dir.display());
+    println!("cargo:rustc-link-lib=static=op_auth");
+
+    // System libraries the static library's TLS/network stack expects.
+    if target.contains("apple-darwin") {
+        println!("cargo:rustc-link-lib=framework=Security");
+        println!("cargo:rustc-link-lib=framework=CoreFoundation");
+    } else if target.contains("windows-msvc") {
+        println!("cargo:rustc-link-lib=ws2_32");
+        println!("cargo:rustc-link-lib=bcrypt");
+        println!("cargo:rustc-link-lib=advapi32");
+        println!("cargo:rustc-link-lib=ntdll");
+    }
+}
diff --git a/crates/op-auth-bridge/prebuilt/aarch64-apple-darwin/VERSION b/crates/op-auth-bridge/prebuilt/aarch64-apple-darwin/VERSION
new file mode 100644
index 000000000..ee94dd834
--- /dev/null
+++ b/crates/op-auth-bridge/prebuilt/aarch64-apple-darwin/VERSION
@@ -0,0 +1 @@
+0.8.3
diff --git a/crates/op-auth-bridge/prebuilt/aarch64-apple-darwin/libop_auth.a b/crates/op-auth-bridge/prebuilt/aarch64-apple-darwin/libop_auth.a
new file mode 100644
index 000000000..2667abbb2
Binary files /dev/null and b/crates/op-auth-bridge/prebuilt/aarch64-apple-darwin/libop_auth.a differ
diff --git a/crates/op-auth-bridge/src/lib.rs b/crates/op-auth-bridge/src/lib.rs
new file mode 100644
index 000000000..3e570ed71
--- /dev/null
+++ b/crates/op-auth-bridge/src/lib.rs
@@ -0,0 +1,94 @@
+//! Bridge to the proprietary op-auth client library.
+//!
+//! The real device-login implementation lives in the private
+//! `ZSeven-W/op-platform` repository and ships as a prebuilt C-ABI static
+//! library committed under `prebuilt/<target>/libop_auth.a`. When no
+//! artifact exists for the current target — or its ABI version does not
+//! match [`REQUIRED_ABI_VERSION`] — this crate falls back to a stub whose
+//! [`available`] returns false, and hosts keep the account UI hidden.
+//!
+//! Poll model: [`login_begin`] returns a handle the host polls each frame
+//! via [`poll`]; handle [`SESSION_HANDLE`] reports the restored/signed-in
+//! session. All strings cross the FFI as UTF-8 pointer + length and are
+//! freed by the bridge immediately after copying.
+
+mod status;
+
+#[cfg(op_auth_prebuilt)]
+#[path = "real.rs"]
+mod backend;
+
+#[cfg(not(op_auth_prebuilt))]
+#[path = "stub.rs"]
+mod backend;
+
+use std::path::PathBuf;
+
+pub use status::AuthStatus;
+
+/// ABI revision this bridge understands; must match the library's
+/// `op_auth_abi_version()`.
+pub const REQUIRED_ABI_VERSION: u32 = 1;
+
+/// `poll` handle that reports the signed-in session instead of a flow.
+pub const SESSION_HANDLE: u64 = 0;
+
+/// Everything the runtime needs at startup.
+#[derive(Clone, Debug)]
+pub struct AuthInitConfig {
+    /// SSO origin, e.g. `https://sso.zseven.cn` (override via
+    /// `OPENPENCIL_SSO_URL` for local development).
+    pub base_url: String,
+    /// Directory owning the persisted credential file.
+    pub storage_dir: PathBuf,
+    pub device_name: String,
+    pub app_version: String,
+}
+
+/// Whether a working auth backend is linked into this build.
+pub fn available() -> bool {
+    backend::available()
+}
+
+/// Initialize the runtime once per process; returns false when the
+/// backend is unavailable or already initialized.
+pub fn init(config: &AuthInitConfig) -> bool {
+    backend::init(config)
+}
+
+/// Load a persisted session, if any; the profile then arrives via
+/// `poll(SESSION_HANDLE)`. Returns whether a credential was restored.
+pub fn restore() -> bool {
+    backend::restore()
+}
+
+/// Start a browser login and return the flow handle (0 when unavailable).
+pub fn login_begin() -> u64 {
+    backend::login_begin()
+}
+
+/// Poll a flow handle (or [`SESSION_HANDLE`]) for its current status.
+pub fn poll(handle: u64) -> AuthStatus {
+    backend::poll(handle)
+}
+
+/// Abort an in-flight login flow.
+pub fn cancel(handle: u64) {
+    backend::cancel(handle)
+}
+
+/// Drop the local session and revoke the device token server-side.
+pub fn sign_out() {
+    backend::sign_out()
+}
+
+/// The zseven-sso platform identifier for this build target.
+pub fn platform_id() -> &'static str {
+    if cfg!(target_os = "macos") {
+        "desktop_macos"
+    } else if cfg!(target_os = "windows") {
+        "desktop_windows"
+    } else {
+        "desktop_linux"
+    }
+}
diff --git a/crates/op-auth-bridge/src/real.rs b/crates/op-auth-bridge/src/real.rs
new file mode 100644
index 000000000..976246968
--- /dev/null
+++ b/crates/op-auth-bridge/src/real.rs
@@ -0,0 +1,112 @@
+//! Backend backed by the prebuilt proprietary static library. Compiled
+//! only when `build.rs` found `prebuilt/<target>/libop_auth.a`; the ABI
+//! handshake still guards against stale artifacts at runtime.
+
+use std::sync::OnceLock;
+
+use crate::status::AuthStatus;
+use crate::{AuthInitConfig, REQUIRED_ABI_VERSION};
+
+#[repr(C)]
+struct OpAuthStatus {
+    code: i32,
+    payload: *mut u8,
+    payload_len: usize,
+}
+
+extern "C" {
+    fn op_auth_abi_version() -> u32;
+    fn op_auth_runtime_init(config_json: *const u8, len: usize) -> bool;
+    fn op_auth_restore() -> i32;
+    fn op_auth_login_begin() -> u64;
+    fn op_auth_poll(handle: u64, out: *mut OpAuthStatus) -> i32;
+    fn op_auth_cancel(handle: u64);
+    fn op_auth_sign_out();
+    fn op_auth_string_free(ptr: *mut u8, len: usize);
+}
+
+pub(crate) fn available() -> bool {
+    static ABI_OK: OnceLock<bool> = OnceLock::new();
+    *ABI_OK.get_or_init(|| {
+        // SAFETY: no arguments; the symbol exists whenever this module compiles.
+        let version = unsafe { op_auth_abi_version() };
+        let matches = version == REQUIRED_ABI_VERSION;
+        if !matches {
+            eprintln!(
+                "op-auth-bridge: prebuilt library ABI {version} does not match \
+                 required {REQUIRED_ABI_VERSION}; account features disabled"
+            );
+        }
+        matches
+    })
+}
+
+pub(crate) fn init(config: &AuthInitConfig) -> bool {
+    if !available() {
+        return false;
+    }
+    let json = serde_json::json!({
+        "base_url": config.base_url,
+        "storage_dir": config.storage_dir.to_string_lossy(),
+        "device_name": config.device_name,
+        "platform": crate::platform_id(),
+        "app_version": config.app_version,
+    })
+    .to_string();
+    // SAFETY: pointer/length describe the live `json` buffer.
+    unsafe { op_auth_runtime_init(json.as_ptr(), json.len()) }
+}
+
+pub(crate) fn restore() -> bool {
+    if !available() {
+        return false;
+    }
+    // SAFETY: no pointer arguments.
+    unsafe { op_auth_restore() == 1 }
+}
+
+pub(crate) fn login_begin() -> u64 {
+    if !available() {
+        return 0;
+    }
+    // SAFETY: no pointer arguments.
+    unsafe { op_auth_login_begin() }
+}
+
+pub(crate) fn poll(handle: u64) -> AuthStatus {
+    if !available() {
+        return AuthStatus::Idle;
+    }
+    let mut raw = OpAuthStatus {
+        code: 0,
+        payload: std::ptr::null_mut(),
+        payload_len: 0,
+    };
+    // SAFETY: `raw` is a valid out-pointer for the duration of the call.
+    let code = unsafe { op_auth_poll(handle, &mut raw) };
+    let payload = if raw.payload.is_null() {
+        None
+    } else {
+        // SAFETY: the library handed us `payload_len` readable bytes that we
+        // free exactly once after copying.
+        let bytes = unsafe { std::slice::from_raw_parts(raw.payload, raw.payload_len) };
+        let text = String::from_utf8_lossy(bytes).into_owned();
+        unsafe { op_auth_string_free(raw.payload, raw.payload_len) };
+        Some(text)
+    };
+    AuthStatus::decode(code, payload.as_deref())
+}
+
+pub(crate) fn cancel(handle: u64) {
+    if available() {
+        // SAFETY: no pointer arguments.
+        unsafe { op_auth_cancel(handle) };
+    }
+}
+
+pub(crate) fn sign_out() {
+    if available() {
+        // SAFETY: no pointer arguments.
+        unsafe { op_auth_sign_out() };
+    }
+}
diff --git a/crates/op-auth-bridge/src/status.rs b/crates/op-auth-bridge/src/status.rs
new file mode 100644
index 000000000..43fcd6755
--- /dev/null
+++ b/crates/op-auth-bridge/src/status.rs
@@ -0,0 +1,114 @@
+//! Status snapshots surfaced to hosts, decoded from FFI payload JSON.
+
+/// Mirror of the library's status codes; payload shapes documented per
+/// variant. Unknown codes decode to [`AuthStatus::Idle`].
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum AuthStatus {
+    /// Session handle: signed out. Flow handle: unknown handle.
+    Idle,
+    /// Login flow: start request in flight.
+    Starting,
+    /// Waiting for the user to approve in the browser; the host opens
+    /// `verification_uri` the first time it observes this state.
+    WaitingApproval {
+        verification_uri: String,
+    },
+    /// Approved; exchanging the pairing for a device token.
+    Exchanging,
+    /// Signed in (terminal for flows; steady state for the session).
+    SignedIn {
+        display_name: String,
+        primary_email: Option<String>,
+        avatar_url: Option<String>,
+        device_id: String,
+    },
+    /// Terminal failure; `code` is one of `denied`, `expired`, `network`,
+    /// `protocol`, `server`.
+    Error {
+        code: String,
+    },
+    Canceled,
+}
+
+impl AuthStatus {
+    pub fn is_terminal(&self) -> bool {
+        matches!(
+            self,
+            AuthStatus::SignedIn { .. } | AuthStatus::Error { .. } | AuthStatus::Canceled
+        )
+    }
+
+    /// Decode one FFI observation. Used by the real backend; the stub
+    /// never produces payloads (hence dead code in stub builds).
+    #[cfg_attr(not(op_auth_prebuilt), allow(dead_code))]
+    pub(crate) fn decode(code: i32, payload: Option<&str>) -> Self {
+        let field = |key: &str| -> Option<String> {
+            let parsed: serde_json::Value = serde_json::from_str(payload?).ok()?;
+            parsed[key].as_str().map(str::to_string)
+        };
+        match code {
+            1 => AuthStatus::Starting,
+            2 => AuthStatus::WaitingApproval {
+                verification_uri: field("verification_uri").unwrap_or_default(),
+            },
+            3 => AuthStatus::Exchanging,
+            4 => AuthStatus::SignedIn {
+                display_name: field("display_name").unwrap_or_default(),
+                primary_email: field("primary_email"),
+                avatar_url: field("avatar_url"),
+                device_id: field("device_id").unwrap_or_default(),
+            },
+            5 => AuthStatus::Error {
+                code: field("code").unwrap_or_else(|| "protocol".to_string()),
+            },
+            6 => AuthStatus::Canceled,
+            _ => AuthStatus::Idle,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn decodes_signed_in_payload() {
+        let payload = r#"{"display_name":"Kay","primary_email":"kay@example.com","avatar_url":null,"device_id":"d1"}"#;
+        assert_eq!(
+            AuthStatus::decode(4, Some(payload)),
+            AuthStatus::SignedIn {
+                display_name: "Kay".to_string(),
+                primary_email: Some("kay@example.com".to_string()),
+                avatar_url: None,
+                device_id: "d1".to_string(),
+            }
+        );
+    }
+
+    #[test]
+    fn decodes_waiting_approval_and_error() {
+        assert_eq!(
+            AuthStatus::decode(2, Some(r#"{"verification_uri":"https://x/login"}"#)),
+            AuthStatus::WaitingApproval {
+                verification_uri: "https://x/login".to_string()
+            }
+        );
+        assert_eq!(
+            AuthStatus::decode(5, Some(r#"{"code":"denied"}"#)),
+            AuthStatus::Error {
+                code: "denied".to_string()
+            }
+        );
+    }
+
+    #[test]
+    fn unknown_codes_and_garbage_payloads_are_safe() {
+        assert_eq!(AuthStatus::decode(99, None), AuthStatus::Idle);
+        assert_eq!(
+            AuthStatus::decode(5, Some("not json")),
+            AuthStatus::Error {
+                code: "protocol".to_string()
+            }
+        );
+    }
+}
diff --git a/crates/op-auth-bridge/src/stub.rs b/crates/op-auth-bridge/src/stub.rs
new file mode 100644
index 000000000..885911c00
--- /dev/null
+++ b/crates/op-auth-bridge/src/stub.rs
@@ -0,0 +1,52 @@
+//! Fallback backend for builds without a prebuilt auth library: every
+//! operation is a no-op and `available()` is false, so hosts keep the
+//! account UI hidden while the build stays green on every platform.
+
+use crate::status::AuthStatus;
+use crate::AuthInitConfig;
+
+pub(crate) fn available() -> bool {
+    false
+}
+
+pub(crate) fn init(_config: &AuthInitConfig) -> bool {
+    false
+}
+
+pub(crate) fn restore() -> bool {
+    false
+}
+
+pub(crate) fn login_begin() -> u64 {
+    0
+}
+
+pub(crate) fn poll(_handle: u64) -> AuthStatus {
+    AuthStatus::Idle
+}
+
+pub(crate) fn cancel(_handle: u64) {}
+
+pub(crate) fn sign_out() {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::path::PathBuf;
+
+    #[test]
+    fn stub_is_inert() {
+        assert!(!available());
+        assert!(!init(&AuthInitConfig {
+            base_url: "https://sso.example".to_string(),
+            storage_dir: PathBuf::from("/tmp"),
+            device_name: "test".to_string(),
+            app_version: "0.0.0".to_string(),
+        }));
+        assert!(!restore());
+        assert_eq!(login_begin(), 0);
+        assert_eq!(poll(0), AuthStatus::Idle);
+        cancel(1);
+        sign_out();
+    }
+}
diff --git a/crates/op-host-desktop/Cargo.toml b/crates/op-host-desktop/Cargo.toml
index 5b8abd9c3..56331948c 100644
--- a/crates/op-host-desktop/Cargo.toml
+++ b/crates/op-host-desktop/Cargo.toml
@@ -82,6 +82,8 @@ op-editor-core = { path = "../op-editor-core" }
 op-editor-host-core = { path = "../op-editor-host-core" }
 # Shared `~/.openpencil` well-known paths used by CLI and desktop discovery.
 op-config-store = { path = "../op-config-store" }
+# Device-login bridge (prebuilt proprietary library or inert stub).
+op-auth-bridge = { path = "../op-auth-bridge" }
 # D′ architecture: pre-validation adapter translates PlannedFix → EditorCommand.
 op-design-lint = { path = "../op-design-lint" }
 # AI code-generation pipeline. The `ai` feature compiles the pull-based
diff --git a/crates/op-host-desktop/src/app_handler.rs b/crates/op-host-desktop/src/app_handler.rs
index ac5afee59..4b45a3060 100644
--- a/crates/op-host-desktop/src/app_handler.rs
+++ b/crates/op-host-desktop/src/app_handler.rs
@@ -868,6 +868,11 @@ impl ApplicationHandler<DesktopEvent> for DesktopApp {
                 if self.poll_update_probe() {
                     self.redraw_dirty = true;
                 }
+                // Drain the browser device-login flow (status + browser
+                // opens land here).
+                if self.poll_auth_flow() {
+                    self.redraw_dirty = true;
+                }
                 // Drain a finished background `git pull`.
                 if self.poll_git_pull_job() {
                     self.redraw_dirty = true;
@@ -1656,6 +1661,7 @@ impl DesktopApp {
             let deadline = self.clock_start + Duration::from_millis(deadline_ms);
             event_loop.set_control_flow(ControlFlow::WaitUntil(deadline));
         } else if self.update_probe.is_pending()
+            || self.host.auth_flow_active()
             || self.model_probe.is_pending()
             || self.image_search.is_pending()
             || self.image_panel.is_pending()
@@ -1726,6 +1732,7 @@ impl DesktopApp {
             || self.pending_html_paste.is_some()
             || self.host.next_animation_deadline_ms().is_some()
             || self.update_probe.is_pending()
+            || self.host.auth_flow_active()
             || self.model_probe.is_pending()
             || self.image_search.is_pending()
             || self.image_panel.is_pending()
diff --git a/crates/op-host-desktop/src/main.rs b/crates/op-host-desktop/src/main.rs
index eaf6d8b4c..ceece58c8 100644
--- a/crates/op-host-desktop/src/main.rs
+++ b/crates/op-host-desktop/src/main.rs
@@ -393,6 +393,13 @@ impl DesktopApp {
         // — the picker paints the Import row + imported group here, and
         // web leaves the default `false` so those controls stay hidden.
         host.editor_state_mut().editor_ui.font_import_supported = true;
+        // Account gate + session restore. The bridge links the proprietary
+        // auth library when a prebuilt exists for this target; stub builds
+        // keep every account entry point hidden unless the dev fake-login
+        // env is set. Skipped under test like the update / model probes.
+        if !cfg!(test) {
+            init_auth_runtime(&mut host);
+        }
         let kit_browser_open_persisted = Some(host.editor_state().editor_ui.component_browser_open);
         if fit_blank_frame {
             host.fit_content_to_viewport(INITIAL_VIEWPORT_W, INITIAL_VIEWPORT_H);
@@ -870,6 +877,17 @@ impl DesktopApp {
         }
     }
 
+    /// Drain the browser device-login flow: fold bridge status polls
+    /// into UI state and open the verification page (exactly once per
+    /// flow) in the system browser.
+    fn poll_auth_flow(&mut self) -> bool {
+        let changed = self.host.poll_auth();
+        if let Some(url) = self.host.take_pending_browser_url() {
+            update_check::open_url(&url);
+        }
+        changed
+    }
+
     /// Drain the background auto-update probe into `update_status`.
     /// When the probe reports a newer release, offer to open the
     /// download page — once per check.
@@ -1113,6 +1131,46 @@ fn parse_live_mcp_port<I: Iterator<Item = String>>(args: I) -> Option<u16> {
     None
 }
 
+/// Initialize the device-login runtime (proprietary bridge library) and
+/// restore a persisted session, then set the runtime account gate. Stub
+/// builds (no prebuilt library for this target) leave the gate closed
+/// unless `OPENPENCIL_DEV_FAKE_LOGIN=1` re-opens it for UI work.
+fn init_auth_runtime(host: &mut WidgetHostNative) {
+    let dev_fake = std::env::var("OPENPENCIL_DEV_FAKE_LOGIN").as_deref() == Ok("1");
+    let mut backend_ready = false;
+    if op_auth_bridge::available() {
+        if let Ok(dir) = op_config_store::openpencil_dir() {
+            let config = op_auth_bridge::AuthInitConfig {
+                // Local-dev override: point the flow at a locally served
+                // zseven-sso (e.g. http://127.0.0.1:5173).
+                base_url: std::env::var("OPENPENCIL_SSO_URL")
+                    .unwrap_or_else(|_| "https://sso.zseven.cn".to_string()),
+                storage_dir: dir.join("auth"),
+                device_name: format!("OpenPencil Desktop ({})", std::env::consts::OS),
+                app_version: env!("CARGO_PKG_VERSION").to_string(),
+            };
+            if op_auth_bridge::init(&config) {
+                backend_ready = true;
+                if op_auth_bridge::restore() {
+                    if let op_auth_bridge::AuthStatus::SignedIn {
+                        display_name,
+                        primary_email,
+                        ..
+                    } = op_auth_bridge::poll(op_auth_bridge::SESSION_HANDLE)
+                    {
+                        host.editor_state_mut().editor_ui.account =
+                            op_editor_core::AccountState::SignedIn {
+                                handle: primary_email.unwrap_or_else(|| display_name.clone()),
+                                display_name,
+                            };
+                    }
+                }
+            }
+        }
+    }
+    host.editor_state_mut().editor_ui.account_ui_available = backend_ready || dev_fake;
+}
+
 /// Pop a native dialog offering to open the download page when a
 /// newer release is found. Yes opens the GitHub releases page.
 fn prompt_update_available(locale: op_editor_core::Locale, version: &str) {
diff --git a/crates/op-host-native/Cargo.toml b/crates/op-host-native/Cargo.toml
index 8b516c2c5..fc78e4ba8 100644
--- a/crates/op-host-native/Cargo.toml
+++ b/crates/op-host-native/Cargo.toml
@@ -67,6 +67,9 @@ serde_json = { workspace = true }
 # `op_editor_core::EditorState`. The host derives a read-only paint
 # `Document` from it each frame (see `widget_host.rs`).
 op-editor-core = { path = "../op-editor-core" }
+# Device-login client bridge — links the proprietary prebuilt library when
+# one exists for the target, else compiles an inert stub (login hidden).
+op-auth-bridge = { path = "../op-auth-bridge" }
 op-i18n = { path = "../op-i18n" }
 
 # Native-only deps cfg-gated outside wasm32. This is critical (resolves codex round 2 B1 BLOCK):
diff --git a/crates/op-host-native/src/widget_host.rs b/crates/op-host-native/src/widget_host.rs
index f52293afc..bf7989183 100644
--- a/crates/op-host-native/src/widget_host.rs
+++ b/crates/op-host-native/src/widget_host.rs
@@ -52,6 +52,7 @@ mod agent_settings_image_gen_tests;
 mod agent_settings_tests;
 mod ai_chat_geometry;
 mod arc_drag;
+mod auth_flow;
 mod blur_inputs;
 #[cfg(test)]
 mod blur_inputs_tests;
@@ -396,6 +397,17 @@ pub struct WidgetHostNative {
     /// Last viewport size seen by paint/press. Used by handlers
     /// that don't receive viewport dims (e.g. apply_cursor_move
     /// driving the color-picker drag).
+    /// In-flight browser device-login flow handle from `op-auth-bridge`
+    /// (`None` = no login running). Polled by the desktop event loop via
+    /// [`Self::poll_auth`].
+    pub(in crate::widget_host) auth_login_handle: Option<u64>,
+    /// Verification URL waiting for the desktop host to open in the
+    /// system browser (drained by `take_pending_browser_url`).
+    pub(in crate::widget_host) auth_pending_browser_url: Option<String>,
+    /// Whether the current flow's verification URL was already queued —
+    /// the flow reports `WaitingApproval` every poll, but the browser
+    /// must open exactly once.
+    pub(in crate::widget_host) auth_browser_opened: bool,
     pub(in crate::widget_host) last_viewport_w: f32,
     pub(in crate::widget_host) last_viewport_h: f32,
     /// Live canvas Preview (Play) session — `Some` while
@@ -783,6 +795,9 @@ impl WidgetHostNative {
             chat_panel_owner: op_editor_ui::widgets::AIChatPlaceholder::next_owner(),
             layer_panel_owner: op_editor_ui::widgets::LayerPanel::next_layer_panel_owner(),
             last_chat_session_index,
+            auth_login_handle: None,
+            auth_pending_browser_url: None,
+            auth_browser_opened: false,
         }
     }
 
diff --git a/crates/op-host-native/src/widget_host/account_press.rs b/crates/op-host-native/src/widget_host/account_press.rs
index 00c550fe5..3ef125185 100644
--- a/crates/op-host-native/src/widget_host/account_press.rs
+++ b/crates/op-host-native/src/widget_host/account_press.rs
@@ -31,30 +31,35 @@ impl WidgetHostNative {
                 .map(op_editor_core::ButtonPressTarget::LoginModal);
         match hit {
             LoginModalHit::Close => {
+                self.cancel_auth_login();
                 self.editor_state.editor_ui.login_modal_open = false;
                 self.editor_state.editor_ui.login_modal_hover = None;
                 self.editor_state.editor_ui.login_modal_stub_hint_shown = false;
             }
             LoginModalHit::Outside => {
                 self.blur_text_inputs_on_blank_press();
+                self.cancel_auth_login();
                 self.editor_state.editor_ui.login_modal_open = false;
                 self.editor_state.editor_ui.login_modal_hover = None;
                 self.editor_state.editor_ui.login_modal_stub_hint_shown = false;
             }
             LoginModalHit::SignIn => {
-                // Dev/demo fast path — never reachable in a production
-                // build; the planned real flow uses OIDC Auth Code +
-                // PKCE via the system browser.
                 if dev_fake_login_enabled() {
+                    // Dev/demo fast path — exercises the signed-in UI
+                    // without a backend.
                     self.editor_state.editor_ui.account =
                         op_editor_core::AccountState::dev_fake_signed_in();
                     self.editor_state.editor_ui.login_modal_open = false;
                     self.editor_state.editor_ui.login_modal_hover = None;
                     self.editor_state.editor_ui.login_modal_stub_hint_shown = false;
+                } else if op_auth_bridge::available() {
+                    // Real flow: browser pairing against zseven-sso via
+                    // the proprietary client library; progress lands in
+                    // `login_modal_status` through `poll_auth`.
+                    self.begin_browser_login();
                 } else {
-                    // Honest stub: no session is created — just reveal
-                    // the "coming soon" note instead of pretending the
-                    // OIDC flow ran.
+                    // Honest stub (no auth library linked): no session is
+                    // created — just reveal the "coming soon" note.
                     self.editor_state.editor_ui.login_modal_stub_hint_shown = true;
                 }
             }
@@ -103,6 +108,9 @@ impl WidgetHostNative {
             Some(AccountMenuRow::SignOut) => {
                 self.close_account_menu();
                 self.editor_state.editor_ui.account = op_editor_core::AccountState::Anonymous;
+                // Revoke the device session (background thread inside the
+                // library; an inert no-op in stub builds).
+                op_auth_bridge::sign_out();
             }
             None => {
                 if !(menu_rect).contains(point) {
diff --git a/crates/op-host-native/src/widget_host/account_press_tests.rs b/crates/op-host-native/src/widget_host/account_press_tests.rs
index dfdbebd52..23789e919 100644
--- a/crates/op-host-native/src/widget_host/account_press_tests.rs
+++ b/crates/op-host-native/src/widget_host/account_press_tests.rs
@@ -103,8 +103,11 @@ fn account_release_gate_blocks_menu_for_signed_in_state() {
 
 #[test]
 fn stale_login_modal_state_does_not_dispatch_while_release_gate_is_hidden() {
-    const { assert!(!op_editor_ui::widgets::ACCOUNT_UI_AVAILABLE) };
     let mut host = WidgetHostNative::new();
+    assert!(
+        !host.editor_state().editor_ui.account_ui_available,
+        "the runtime account gate must default to off"
+    );
     host.editor_state_mut().editor_ui.login_modal_open = true;
 
     let modal = LoginModal::for_editor(host.editor_state());
@@ -124,8 +127,11 @@ fn stale_login_modal_state_does_not_dispatch_while_release_gate_is_hidden() {
 
 #[test]
 fn stale_account_menu_state_does_not_dispatch_while_release_gate_is_hidden() {
-    const { assert!(!op_editor_ui::widgets::ACCOUNT_UI_AVAILABLE) };
     let mut host = WidgetHostNative::new();
+    assert!(
+        !host.editor_state().editor_ui.account_ui_available,
+        "the runtime account gate must default to off"
+    );
     let signed_in = AccountState::SignedIn {
         display_name: "Fini".into(),
         handle: "fini".into(),
@@ -175,7 +181,17 @@ fn login_modal_sign_in_without_dev_flag_shows_honest_stub_hint() {
         AccountState::Anonymous
     );
     assert!(host.editor_state().editor_ui.login_modal_open);
-    assert!(host.editor_state().editor_ui.login_modal_stub_hint_shown);
+    if op_auth_bridge::available() {
+        // Real auth library linked: the press starts the browser flow
+        // instead of the stub hint. The runtime is uninitialized under
+        // test, so the flow settles into a failure note — never a session.
+        assert!(!host.editor_state().editor_ui.login_modal_stub_hint_shown);
+        assert!(host.editor_state().editor_ui.login_modal_status.is_some());
+    } else {
+        // Stub build: honest "coming soon" note, no flow started.
+        assert!(host.editor_state().editor_ui.login_modal_stub_hint_shown);
+        assert!(host.editor_state().editor_ui.login_modal_status.is_none());
+    }
     assert_eq!(
         host.editor_state().editor_ui.pressed_button,
         Some(ButtonPressTarget::LoginModal(LoginModalButton::SignIn))
diff --git a/crates/op-host-native/src/widget_host/auth_flow.rs b/crates/op-host-native/src/widget_host/auth_flow.rs
new file mode 100644
index 000000000..c261178f9
--- /dev/null
+++ b/crates/op-host-native/src/widget_host/auth_flow.rs
@@ -0,0 +1,116 @@
+//! Browser device-login flow driver: bridges `op-auth-bridge` status
+//! polls into editor UI state. The desktop event loop calls
+//! [`WidgetHostNative::poll_auth`] from its background-drain pass and
+//! opens URLs drained via [`WidgetHostNative::take_pending_browser_url`]
+//! — this module never spawns processes itself.
+
+use super::WidgetHostNative;
+use op_auth_bridge::AuthStatus;
+use op_editor_core::{AccountState, LoginFlowError, LoginFlowStatus};
+
+impl WidgetHostNative {
+    /// Start the browser device-login flow (called from the sign-in
+    /// modal's primary button when a real auth backend is linked).
+    pub(in crate::widget_host) fn begin_browser_login(&mut self) {
+        if self.auth_login_handle.is_some() {
+            return; // one flow at a time; the running one owns the modal
+        }
+        let handle = op_auth_bridge::login_begin();
+        if handle == 0 {
+            self.editor_state.editor_ui.login_modal_status =
+                Some(LoginFlowStatus::Failed(LoginFlowError::Unavailable));
+            return;
+        }
+        self.auth_login_handle = Some(handle);
+        self.auth_browser_opened = false;
+        self.editor_state.editor_ui.login_modal_status = Some(LoginFlowStatus::WaitingBrowser);
+        self.editor_state.editor_ui.login_modal_stub_hint_shown = false;
+    }
+
+    /// Abort an in-flight login (modal closed / outside click). The
+    /// bridge flow settles into Canceled on its own thread; UI state
+    /// resets immediately.
+    pub fn cancel_auth_login(&mut self) {
+        if let Some(handle) = self.auth_login_handle.take() {
+            op_auth_bridge::cancel(handle);
+        }
+        self.auth_browser_opened = false;
+        self.auth_pending_browser_url = None;
+        self.editor_state.editor_ui.login_modal_status = None;
+    }
+
+    /// Whether a login flow is running — drives the desktop event loop's
+    /// periodic wakeups so status changes land while the app idles.
+    pub fn auth_flow_active(&self) -> bool {
+        self.auth_login_handle.is_some()
+    }
+
+    /// The verification URL the host should open in the system browser,
+    /// at most once per flow.
+    pub fn take_pending_browser_url(&mut self) -> Option<String> {
+        self.auth_pending_browser_url.take()
+    }
+
+    /// Poll the in-flight login flow (and the restored session) and fold
+    /// status changes into editor UI state. Returns whether anything
+    /// visible changed.
+    pub fn poll_auth(&mut self) -> bool {
+        let Some(handle) = self.auth_login_handle else {
+            return false;
+        };
+        let ui = &mut self.editor_state.editor_ui;
+        let previous = ui.login_modal_status;
+        match op_auth_bridge::poll(handle) {
+            AuthStatus::Idle | AuthStatus::Starting => {
+                ui.login_modal_status = Some(LoginFlowStatus::WaitingBrowser);
+            }
+            AuthStatus::WaitingApproval { verification_uri } => {
+                ui.login_modal_status = Some(LoginFlowStatus::WaitingApproval);
+                if !self.auth_browser_opened && !verification_uri.is_empty() {
+                    self.auth_browser_opened = true;
+                    self.auth_pending_browser_url = Some(verification_uri);
+                }
+            }
+            AuthStatus::Exchanging => {
+                ui.login_modal_status = Some(LoginFlowStatus::Exchanging);
+            }
+            AuthStatus::SignedIn {
+                display_name,
+                primary_email,
+                ..
+            } => {
+                ui.account = AccountState::SignedIn {
+                    handle: primary_email.unwrap_or_else(|| display_name.clone()),
+                    display_name,
+                };
+                ui.login_modal_status = None;
+                ui.login_modal_open = false;
+                ui.login_modal_hover = None;
+                self.auth_login_handle = None;
+                self.auth_browser_opened = false;
+                self.mark_dirty();
+                return true;
+            }
+            AuthStatus::Error { code } => {
+                ui.login_modal_status = Some(LoginFlowStatus::Failed(match code.as_str() {
+                    "denied" => LoginFlowError::Denied,
+                    "expired" => LoginFlowError::Expired,
+                    _ => LoginFlowError::Unavailable,
+                }));
+                self.auth_login_handle = None;
+                self.auth_browser_opened = false;
+            }
+            AuthStatus::Canceled => {
+                ui.login_modal_status = None;
+                self.auth_login_handle = None;
+                self.auth_browser_opened = false;
+            }
+        }
+        let changed = self.editor_state.editor_ui.login_modal_status != previous
+            || self.auth_pending_browser_url.is_some();
+        if changed {
+            self.mark_dirty();
+        }
+        changed
+    }
+}
diff --git a/crates/op-host-native/src/widget_host/input.rs b/crates/op-host-native/src/widget_host/input.rs
index a2dab82d4..212f785c3 100644
--- a/crates/op-host-native/src/widget_host/input.rs
+++ b/crates/op-host-native/src/widget_host/input.rs
@@ -580,7 +580,7 @@ impl WidgetHostNative {
         }
         // Sign-in modal — owns the cursor while open. Hover the close
         // `✕` + the primary sign-in button.
-        if op_editor_ui::widgets::ACCOUNT_UI_AVAILABLE
+        if self.editor_state.editor_ui.account_ui_available
             && self.editor_state.editor_ui.login_modal_open
         {
             use op_editor_ui::widgets::login_modal::LoginModal;
@@ -597,7 +597,7 @@ impl WidgetHostNative {
             return changed;
         }
         // Signed-in account dropdown — owns the cursor while open.
-        if op_editor_ui::widgets::ACCOUNT_UI_AVAILABLE
+        if self.editor_state.editor_ui.account_ui_available
             && self.editor_state.editor_ui.account_menu_open
         {
             use op_editor_ui::widgets::account_menu::AccountMenu;
diff --git a/crates/op-host-native/src/widget_host/paint.rs b/crates/op-host-native/src/widget_host/paint.rs
index c15bf9afd..f4dcf208c 100644
--- a/crates/op-host-native/src/widget_host/paint.rs
+++ b/crates/op-host-native/src/widget_host/paint.rs
@@ -589,7 +589,7 @@ impl WidgetHostNative {
         }
 
         // 10e. Sign-in modal — full-viewport scrim + centred card.
-        if op_editor_ui::widgets::ACCOUNT_UI_AVAILABLE && ui.login_modal_open {
+        if ui.account_ui_available && ui.login_modal_open {
             use op_editor_ui::widgets::login_modal::LoginModal;
             frame.fill_rect(
                 Rect {
@@ -614,7 +614,7 @@ impl WidgetHostNative {
         // 10f. Signed-in account dropdown — anchored under the TopBar
         //      avatar button, no scrim (same tier as the file menu /
         //      locale picker).
-        if op_editor_ui::widgets::ACCOUNT_UI_AVAILABLE && ui.account_menu_open {
+        if ui.account_ui_available && ui.account_menu_open {
             use op_editor_ui::widgets::account_menu::AccountMenu;
             let top_bar_rect = Rect {
                 origin: Point2D::new(0.0, 0.0),
diff --git a/crates/op-host-native/src/widget_host/press.rs b/crates/op-host-native/src/widget_host/press.rs
index 688df8beb..4c2c5b493 100644
--- a/crates/op-host-native/src/widget_host/press.rs
+++ b/crates/op-host-native/src/widget_host/press.rs
@@ -396,7 +396,7 @@ impl WidgetHostNative {
             self.dispatch_figma_import_press(x, y, viewport_width, viewport_height);
             return true;
         }
-        if op_editor_ui::widgets::ACCOUNT_UI_AVAILABLE
+        if self.editor_state.editor_ui.account_ui_available
             && self.editor_state.editor_ui.login_modal_open
         {
             self.close_image_popovers_for_higher_overlay();
@@ -407,7 +407,7 @@ impl WidgetHostNative {
         // 0a'. Account dropdown — anchored under the TopBar avatar
         // button; must hit-test before the TopBar's own block so a
         // re-click on the avatar closes rather than re-toggling.
-        if op_editor_ui::widgets::ACCOUNT_UI_AVAILABLE
+        if self.editor_state.editor_ui.account_ui_available
             && self.editor_state.editor_ui.account_menu_open
         {
             self.close_image_popovers_for_higher_overlay();
@@ -633,7 +633,7 @@ impl WidgetHostNative {
                     return true;
                 }
                 TopBarHit::Account => {
-                    if !op_editor_ui::widgets::ACCOUNT_UI_AVAILABLE {
+                    if !self.editor_state.editor_ui.account_ui_available {
                         return false;
                     }
                     if self.editor_state.editor_ui.account.is_signed_in() {
diff --git a/crates/op-host-native/src/widget_host/shortcuts.rs b/crates/op-host-native/src/widget_host/shortcuts.rs
index ef11763b3..e6ee6eab5 100644
--- a/crates/op-host-native/src/widget_host/shortcuts.rs
+++ b/crates/op-host-native/src/widget_host/shortcuts.rs
@@ -443,7 +443,7 @@ impl WidgetHostNative {
         if ui.figma_import_in_progress
             || !ui.figma_import_pages.is_empty()
             || ui.export_dialog_open
-            || (op_editor_ui::widgets::ACCOUNT_UI_AVAILABLE && ui.login_modal_open)
+            || (ui.account_ui_available && ui.login_modal_open)
             || ui.agent_settings_open
             || (ui.missing_fonts_modal_open
                 && ui
diff --git a/crates/op-host-web/src/widget_host/keyboard_edit_ops.rs b/crates/op-host-web/src/widget_host/keyboard_edit_ops.rs
index b6624a077..9c9441329 100644
--- a/crates/op-host-web/src/widget_host/keyboard_edit_ops.rs
+++ b/crates/op-host-web/src/widget_host/keyboard_edit_ops.rs
@@ -609,7 +609,7 @@ impl WidgetHost {
         if ui.figma_import_in_progress
             || !ui.figma_import_pages.is_empty()
             || ui.export_dialog_open
-            || (op_editor_ui::widgets::ACCOUNT_UI_AVAILABLE && ui.login_modal_open)
+            || (ui.account_ui_available && ui.login_modal_open)
             || ui.agent_settings_open
             || (ui.missing_fonts_modal_open
                 && ui
diff --git a/crates/op-host-web/src/widget_host/press.rs b/crates/op-host-web/src/widget_host/press.rs
index ef68485c1..4b24cab71 100644
--- a/crates/op-host-web/src/widget_host/press.rs
+++ b/crates/op-host-web/src/widget_host/press.rs
@@ -514,9 +514,10 @@ impl WidgetHost {
                     self.editor_state.editor_ui.toggle_preview();
                 }
                 TopBarHit::Account => {
-                    // Unreachable: `ACCOUNT_BUTTON_AVAILABLE` gates the
-                    // avatar button out of the web build's hit-test (the
-                    // sign-in flow is desktop-only).
+                    // Unreachable: `TopBar::account_button_visible` is
+                    // always false on wasm32 (the web host never sets
+                    // `account_ui_available`; the sign-in flow is
+                    // desktop-only), so the avatar never hit-tests here.
                 }
             }
             self.mark_dirty();