feat: device linking, and signing in to the hub with a device key

Stage C. Identity keys are per node, so a browser and a desktop client are two
keys on one account there — and the node refused the second where it accepted
the first. Without this, an account created natively could never be opened in a
browser without an operator code per node, and "a native client must not prevent
web use" would have been dead on arrival.

Device linking (node)
---------------------
`identities` is keyed by `(user_id, pk_ed25519)` instead of `user_id` alone. The
old shape did `INSERT OR REPLACE`, so a second device overwrote the first
silently; SQLite cannot change a primary key in place, so the table is rebuilt.
Existing pins are carried over — verified against a live roster with 10 of them,
nobody re-pairs.

A new device files a request bound by `sha256(code ‖ its own keys)`, and a key
the node **already pinned** countersigns it. The hub cannot: it has stored no
user keys since 2026-08-14, which is what makes this safe to do without an
operator in the loop.

**The code never reaches the node.** It lists this account's pending requests
with their stored hashes; the approver recomputes and keeps the match. A node
offering fabricated keys would have to produce a hash over a code it has never
seen. Nothing rests on a human comparing digits — that ritual was dropped in
12.1 as "correct, unusable as the default" and must not return by the back door.

The design document had the approver look a request up *by* its hash, which is
circular: computing it needs the keys being asked about. Corrected in both.

Revocation marks rather than deletes, because a deleted row is a key the node
would happily pin again — which is the laptop somebody just reported lost. Your
last device cannot be revoked: coming back would need an operator's code.

Hub — the only change in the whole plan
---------------------------------------
`POST /v1/users/auth` signs in with a device Ed25519 key, on the same pattern as
`/v1/nodes/auth`, plus `/v1/users/devices` to register, list and retire. New
`user_devices` table with an Alembic migration, because `create_all()` is not
one.

This is **not** the key directory that was H3, and the tests say so: nothing
reads it but the hub, no group key is ever wrapped for one, and it is a
different key from the per-node identities. What it does cost is metadata — the
hub now knows how many devices an account has and when each last signed in.

Also `client.minimum` / `client.recommended` in `GET /v1/hub/version`: an
installed client meets a newer hub the day the interface ships in a package, and
that is cheap now and awkward to retrofit.

Browser
-------
The `key_changed` refusal becomes `unknown_device` and offers a linking code
instead of telling someone to find their operator. The Members panel lists this
account's devices here, approves one by code, and retires one.

773 tests pass. `e2e.py` gained a step that links a device end to end against
the live deployment — file, list, recompute, countersign, then open the group
with the new keys and no code — and it also gained `recv_type`, because a step
that assumes the next message is its own answer reads an ack left by the step
before.

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

17 files changed, 707 insertions, 1 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/api/hub.py b/packages/meshbay-hub/src/meshbay_hub/api/hub.py
index 6e2db9e..4aef93d 100644
--- a/packages/meshbay-hub/src/meshbay_hub/api/hub.py
+++ b/packages/meshbay-hub/src/meshbay_hub/api/hub.py
@@ -26,6 +26,22 @@ async def hub_pubkey():
     return {"pk_hub_pem": hub_public_key_pem().decode()}
 
 
+# What an installed client must be, to talk to this hub.
+#
+# Until a client ships, the SPA and the hub deploy together and are always in
+# sync: a /v1/ response shape changes and app.js is fixed in the same commit.
+# The moment the interface is installed rather than served, an old client meets
+# a new hub — for the first time in this project's life — and there is no way to
+# fix it from here.
+#
+# `minimum` refuses; `recommended` warns. Both are stated so a client can tell a
+# user "update to keep using this" before it becomes "this stopped working".
+# Raise `minimum` only for a change a client genuinely cannot survive, and
+# remember store review latency makes that expensive on Android.
+MIN_CLIENT_VERSION = "0.1.0"
+RECOMMENDED_CLIENT_VERSION = "0.1.0"
+
+
 @router.get("/version")
 async def hub_version():
     """Version check endpoint for clients to detect updates."""
@@ -33,4 +49,11 @@ async def hub_version():
         "hub": __version__,
         "mnp": MNP_VERSION,
         "mhp": MHP_VERSION,
+        # A client compares its own version against these before doing anything
+        # else. The browser SPA always matches the hub by construction and can
+        # ignore them.
+        "client": {
+            "minimum": MIN_CLIENT_VERSION,
+            "recommended": RECOMMENDED_CLIENT_VERSION,
+        },
     }
diff --git a/packages/meshbay-hub/src/meshbay_hub/api/users.py b/packages/meshbay-hub/src/meshbay_hub/api/users.py
index 0bfbcac..b5fa205 100644
--- a/packages/meshbay-hub/src/meshbay_hub/api/users.py
+++ b/packages/meshbay-hub/src/meshbay_hub/api/users.py
@@ -1,10 +1,12 @@
 """User endpoints — /v1/users/*"""
 
 import base64
+import time
 import logging
 import uuid
 from datetime import datetime, timezone, timedelta
 
+from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PublicKey
 from fastapi import APIRouter, Depends, HTTPException, Request, status
 from pydantic import BaseModel, field_validator
 from sqlalchemy import delete, select, update
@@ -27,7 +29,7 @@ from meshbay_hub.api.netutil import client_ip
 from meshbay_hub.config import HubConfig
 from meshbay_hub.db.engine import get_db
 from meshbay_hub.db.models import (
-    Group, GroupMember, IPLog, Node, Notification, RefreshToken, User,
+    Group, GroupMember, IPLog, Node, Notification, RefreshToken, User, UserDevice,
 )
 from meshbay_hub.api.deps import get_current_user, require_user_scope
 
@@ -232,6 +234,186 @@ async def login(
     }
 
 
+# ── Device authentication ────────────────────────────────────────────────────
+#
+# A device signs in with an Ed25519 key instead of re-deriving one from the
+# passphrase every time. The passphrase remains the account's credential and its
+# only recovery path; this is the day-to-day path once a device is registered.
+#
+# This is **not** the key directory that was H3, and the difference matters:
+# nothing reads these but the hub, no group key is ever wrapped for one, and it
+# is a different key from the per-node identity keys, which never leave the
+# device-node relationship. What it does cost is metadata — the hub now knows
+# how many devices an account has and when each last signed in.
+
+DEVICE_AUTH_TIMESTAMP_WINDOW = 60  # seconds, as for node auth
+
+
+class DeviceRegisterRequest(BaseModel):
+    pk_auth_ed25519: str          # base64 raw 32 bytes
+    label: str = ""
+
+
+class DeviceAuthRequest(BaseModel):
+    username:  str
+    timestamp: int                # unix epoch seconds
+    signature: str                # base64 Ed25519 over the message below
+
+
+@router.post("/devices", status_code=201)
+async def register_device(
+    body: DeviceRegisterRequest,
+    current_user: User = Depends(require_user_scope),
+    db: AsyncSession = Depends(get_db),
+):
+    """
+    Register a device's hub authentication key.
+
+    Requires an existing session, which in practice means the passphrase was
+    entered on this device a moment ago. A device cannot enrol itself.
+    """
+    try:
+        raw = base64.b64decode(body.pk_auth_ed25519)
+        Ed25519PublicKey.from_public_bytes(raw)
+    except Exception:
+        raise HTTPException(status_code=400, detail="Invalid Ed25519 public key")
+
+    existing = await db.execute(
+        select(UserDevice).where(
+            UserDevice.pk_auth_ed25519 == body.pk_auth_ed25519))
+    found = existing.scalar_one_or_none()
+    if found:
+        if found.user_id != current_user.id:
+            # One key, one account. Sharing it would make "who signed in" a
+            # question with two answers.
+            raise HTTPException(status_code=409,
+                                detail="That key belongs to another account")
+        return {"id": found.id, "label": found.label, "existing": True}
+
+    count = await db.execute(
+        select(UserDevice).where(UserDevice.user_id == current_user.id))
+    if len(count.scalars().all()) >= 10:
+        raise HTTPException(status_code=409,
+                            detail="Too many devices — remove one first")
+
+    device = UserDevice(user_id=current_user.id,
+                        pk_auth_ed25519=body.pk_auth_ed25519,
+                        label=body.label[:64])
+    db.add(device)
+    await db.commit()
+    await db.refresh(device)
+    return {"id": device.id, "label": device.label, "existing": False}
+
+
+@router.get("/devices")
+async def list_devices(
+    current_user: User = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    result = await db.execute(
+        select(UserDevice).where(UserDevice.user_id == current_user.id)
+        .order_by(UserDevice.created_at))
+    return {"devices": [
+        {"id": d.id, "label": d.label,
+         "created_at": d.created_at.isoformat() if d.created_at else None,
+         "last_seen": d.last_seen.isoformat() if d.last_seen else None}
+        for d in result.scalars().all()
+    ]}
+
+
+@router.delete("/devices/{device_id}")
+async def delete_device(
+    device_id: str,
+    current_user: User = Depends(require_user_scope),
+    db: AsyncSession = Depends(get_db),
+):
+    """Retire a device's hub key. Its per-node identities are separate and are
+    revoked on each node, which the hub cannot do and should not be able to."""
+    result = await db.execute(
+        select(UserDevice).where(UserDevice.id == device_id,
+                                 UserDevice.user_id == current_user.id))
+    device = result.scalar_one_or_none()
+    if not device:
+        raise HTTPException(status_code=404, detail="No such device")
+    await db.delete(device)
+    await db.commit()
+    return {"status": "deleted", "id": device_id}
+
+
+@router.post("/auth")
+@limiter.limit("10/minute")
+async def device_auth(
+    body: DeviceAuthRequest,
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+):
+    """
+    Sign in with a registered device key. Same shape as `/v1/nodes/auth`.
+
+    The timestamp window is what stops a captured signature being replayed
+    later; the signature covers the username as well, so one collected for a
+    different account is not usable here.
+    """
+    now = int(time.time())
+    if abs(now - body.timestamp) > DEVICE_AUTH_TIMESTAMP_WINDOW:
+        raise HTTPException(status_code=401,
+                            detail="Timestamp too old or too far in the future")
+
+    result = await db.execute(select(User).where(User.username == body.username))
+    user = result.scalar_one_or_none()
+    if not user:
+        raise HTTPException(status_code=401, detail="Invalid credentials")
+    if user.status != "active":
+        raise HTTPException(status_code=403, detail=f"Account {user.status}")
+
+    devices = await db.execute(
+        select(UserDevice).where(UserDevice.user_id == user.id))
+    message = f"meshbay:user_auth:{body.username}:{body.timestamp}".encode()
+    try:
+        sig = base64.b64decode(body.signature)
+    except Exception:
+        raise HTTPException(status_code=401, detail="Invalid signature encoding")
+
+    matched = None
+    for device in devices.scalars().all():
+        try:
+            pk = Ed25519PublicKey.from_public_bytes(
+                base64.b64decode(device.pk_auth_ed25519))
+            pk.verify(sig, message)
+        except Exception:
+            continue
+        matched = device
+        break
+
+    if matched is None:
+        db.add(IPLog(user_id=user.id, event="device_auth_fail",
+                     ip_address=client_ip(request), detail=body.username))
+        await db.commit()
+        raise HTTPException(status_code=401, detail="Invalid signature")
+
+    matched.last_seen = datetime.now(timezone.utc)
+
+    memberships = await db.execute(
+        select(GroupMember.group_id).where(GroupMember.user_id == user.id))
+    group_ids = [gid for (gid,) in memberships.all()]
+    access_token = issue_access_token(user.id, ttl=_ttl(), groups=group_ids)
+    raw_rt, rt_hash = generate_refresh_token()
+    expires_at = datetime.now(timezone.utc) + timedelta(seconds=_refresh_ttl())
+    db.add(RefreshToken(user_id=user.id, token_hash=rt_hash,
+                        family_id=str(uuid.uuid4()), expires_at=expires_at))
+    db.add(IPLog(user_id=user.id, event="device_auth",
+                 ip_address=client_ip(request)))
+    await db.commit()
+
+    return {
+        "access_token":  access_token,
+        "refresh_token": raw_rt,
+        "token_type":    "bearer",
+        "expires_in":    _ttl(),
+        "device_id":     matched.id,
+    }
+
+
 @router.post("/token/refresh")
 @limiter.limit("20/minute")
 async def token_refresh(
diff --git a/packages/meshbay-hub/src/meshbay_hub/db/migrations/versions/e5a2b7d31f88_user_device_auth_keys.py b/packages/meshbay-hub/src/meshbay_hub/db/migrations/versions/e5a2b7d31f88_user_device_auth_keys.py
new file mode 100644
index 0000000..ddada15
--- /dev/null
+++ b/packages/meshbay-hub/src/meshbay_hub/db/migrations/versions/e5a2b7d31f88_user_device_auth_keys.py
@@ -0,0 +1,47 @@
+"""user device auth keys
+
+Device Ed25519 authentication to the hub, so a client signs in without
+re-deriving a key from the passphrase every time.
+
+Deliberately **not** the key directory that was H3: nothing reads this but the
+hub itself, nobody wraps a group key for it, and it is a different key from the
+per-node identity keys, which never leave the device-node relationship. See
+`docs/desktop-client-v1.md` §5.
+
+`create_all()` is not a migration — it creates missing tables and never a
+missing column, so a schema change without a file here reaches the tests (fresh
+DB every run) and never reaches the deployed hub.
+
+Revision ID: e5a2b7d31f88
+Revises: 3dc91cd4ea52
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "e5a2b7d31f88"
+down_revision: Union[str, Sequence[str], None] = "3dc91cd4ea52"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "user_devices",
+        sa.Column("id", sa.String(36), primary_key=True),
+        sa.Column("user_id", sa.String(36), sa.ForeignKey("users.id"),
+                  nullable=False),
+        sa.Column("pk_auth_ed25519", sa.String(64), nullable=False, unique=True),
+        sa.Column("label", sa.String(64), nullable=False, server_default=""),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False,
+                  server_default=sa.func.now()),
+        sa.Column("last_seen", sa.DateTime(timezone=True), nullable=True),
+    )
+    op.create_index("ix_user_devices_user", "user_devices", ["user_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_user_devices_user", table_name="user_devices")
+    op.drop_table("user_devices")
diff --git a/packages/meshbay-hub/src/meshbay_hub/db/models.py b/packages/meshbay-hub/src/meshbay_hub/db/models.py
index a220a64..12507a6 100644
--- a/packages/meshbay-hub/src/meshbay_hub/db/models.py
+++ b/packages/meshbay-hub/src/meshbay_hub/db/models.py
@@ -178,6 +178,41 @@ class FederatedGroup(Base):
     )
 
 
+class UserDevice(Base):
+    """
+    A device's key for authenticating **to the hub**, and nothing else.
+
+    This is not a reintroduction of the key directory that was H3, and the
+    distinction is worth being precise about because it looks like one:
+
+      * **Nobody reads this but the hub.** No endpoint publishes it, nothing
+        wraps a group key for it, and no node ever asks for it. H3 was a
+        directory *others* read from, where a substituted key was handed the
+        GEK by an honest member.
+      * **It is not a node identity key.** Those are generated per node, pinned
+        there, and never leave that relationship (`docs/per-node-identity-v1.md`).
+        A device holds one of these *plus* a different key per node, so nothing
+        here correlates a person across operators.
+
+    What it does cost, stated plainly: the hub now knows how many devices an
+    account has and when each one last signed in. That is new metadata, and it
+    is the price of not deriving a key from the passphrase on every sign-in.
+    """
+
+    __tablename__ = "user_devices"
+
+    id:         Mapped[str] = mapped_column(String(36), primary_key=True, default=_uuid)
+    user_id:    Mapped[str] = mapped_column(ForeignKey("users.id"), nullable=False)
+    # base64 raw Ed25519, unique so one device key belongs to one account
+    pk_auth_ed25519: Mapped[str] = mapped_column(String(64), unique=True, nullable=False)
+    label:      Mapped[str] = mapped_column(String(64), default="")
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)
+    last_seen:  Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True)
+
+    __table_args__ = (Index("ix_user_devices_user", "user_id"),)
+
+
 class SwarmSource(Base):
     """
     Tracks which nodes can serve a given content hash (public swarm).
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/app.js b/packages/meshbay-hub/src/meshbay_hub/static/app.js
index 4a4e712..a48535a 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/app.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/app.js
@@ -1252,6 +1252,10 @@ function GroupPage({ groupId, group, token, username, userId, onRefreshAuth,
   // the second one should make the pairing form go away.
   const [operatorPaired, setOperatorPaired] = useState(false);
   const [needsCode, setNeedsCode] = useState(false);
+  // This browser holds a key the node does not know, for an account it does.
+  // Not the operator's problem: a device already paired here can admit it.
+  const [needsDevice, setNeedsDevice] = useState(false);
+  const [deviceCode, setDeviceCode] = useState('');
   const [codeInput, setCodeInput] = useState('');
   const [retryKey, setRetryKey] = useState(0);
   const transportRef = useRef(null);
@@ -1382,6 +1386,11 @@ function GroupPage({ groupId, group, token, username, userId, onRefreshAuth,
         // one-time code from the operator before it will hand over the group
         // key. Not an error to shout about — a step in joining.
         if (err.reason === 'code_required') setNeedsCode(true);
+        // A key this node has never pinned, for an account it knows. The way in
+        // is a device already trusted here, not an operator — which is the
+        // whole point of device linking: a second browser or a native client
+        // must not cost anyone a support request.
+        if (err.reason === 'unknown_device') setNeedsDevice(true);
         setError(err.message);
         setStatus('error');
         // A refusal means the node answered, so it is up; only a failure to
@@ -1865,6 +1874,27 @@ function GroupPage({ groupId, group, token, username, userId, onRefreshAuth,
         `}
       </div>
       ${error && html`<div class="error-msg" style="margin-bottom:12px">${error}</div>`}
+      ${needsDevice && html`
+        <div class="invite-form" style="margin-bottom:12px">
+          <h4>${t('device.add_title')}</h4>
+          <p class="settings-hint">${t('device.add_hint')}</p>
+          ${!deviceCode && html`
+            <button class="admin-btn" onClick=${async () => {
+              try {
+                const transport = transportRef.current;
+                const out = await transport.requestDeviceAdd(userId);
+                setDeviceCode(out.code);
+              } catch (err) { setError(err.message); }
+            }}>${t('device.add_btn')}</button>
+          `}
+          ${deviceCode && html`
+            <p class="settings-hint">${t('device.add_show')}</p>
+            <p style="font-family:monospace;font-size:1.6em;letter-spacing:2px">
+              ${deviceCode}
+            </p>
+          `}
+        </div>
+      `}
       ${needsCode && html`
         <form class="invite-form" style="margin-bottom:12px" onSubmit=${submitJoinCode}>
           <h4>${t('group.join_code_title')}</h4>
@@ -2191,11 +2221,50 @@ function MembersPanel({ groupId, group, token, transportRef, gekRef,
   const [pairCode, setPairCode] = useState('');
   const [pairStatus, setPairStatus] = useState('');
   const [pairing, setPairing] = useState(false);
+  // Your own devices on this node. Not a members feature — it is beside them
+  // because this is where a live connection to the node exists.
+  const [devices, setDevices] = useState([]);
+  const [approveCode, setApproveCode] = useState('');
+  const [deviceMsg, setDeviceMsg] = useState('');
 
   // Pairing lives here rather than in Settings because this is where a live
   // connection to the node exists — and it is offered only when the node itself
   // says this account is its operator (is_node_admin comes from the authenticated
   // handshake_ack, not from the hub).
+  const loadDevices = useCallback(async () => {
+    const transport = transportRef.current;
+    if (!transport || !transport.connected) return;
+    try {
+      const out = await transport.listDevices();
+      setDevices(out.devices);
+    } catch { /* a node that has none says so by listing none */ }
+  }, [transportRef]);
+
+  useEffect(() => { loadDevices(); }, [loadDevices]);
+
+  const approveDevice = useCallback(async (e) => {
+    e.preventDefault();
+    const code = approveCode.trim();
+    if (!code) return;
+    setDeviceMsg('');
+    try {
+      await transportRef.current.approveDevice(userId, code);
+      setApproveCode('');
+      setDeviceMsg(t('device.approved'));
+      await loadDevices();
+    } catch (err) { setDeviceMsg(err.message); }
+  }, [approveCode, userId, transportRef, loadDevices]);
+
+  const revokeDevice = useCallback(async (device) => {
+    if (!confirm(t('device.revoke_confirm'))) return;
+    setDeviceMsg('');
+    try {
+      await transportRef.current.revokeDevice(
+        userId, device.pk_ed25519, device.pk_x25519 || '');
+      await loadDevices();
+    } catch (err) { setDeviceMsg(err.message); }
+  }, [userId, transportRef, loadDevices]);
+
   const doPair = useCallback(async (e) => {
     e.preventDefault();
     const code = pairCode.trim();
@@ -2398,6 +2467,36 @@ function MembersPanel({ groupId, group, token, transportRef, gekRef,
           </div>
         </form>
       `}
+
+      <div class="invite-form" style="margin-top:16px">
+        <h4>${t('device.mine_title')}</h4>
+        <p class="settings-hint">${t('device.mine_hint')}</p>
+        ${deviceMsg && html`<p class="settings-hint">${deviceMsg}</p>`}
+        ${devices.length === 0 && html`
+          <p class="settings-hint">${t('device.mine_empty')}</p>
+        `}
+        ${devices.map(d => html`
+          <div key=${d.pk_ed25519}
+            style="display:flex;align-items:center;gap:8px;margin:4px 0">
+            <span style="font-family:monospace">${d.pk_ed25519.slice(0, 16)}…</span>
+            ${d.is_this_one && html`<span class="badge">${t('device.this_one')}</span>`}
+            <span class="settings-hint">${d.pinned_via}${d.label ? ' · ' + d.label : ''}</span>
+            ${!d.is_this_one && devices.length > 1 && html`
+              <button class="admin-btn" onClick=${() => revokeDevice(d)}>
+                ${t('device.revoke')}
+              </button>
+            `}
+          </div>
+        `)}
+        <form onSubmit=${approveDevice} style="margin-top:12px">
+          <p class="settings-hint">${t('device.approve_hint')}</p>
+          <div style="display:flex;gap:8px">
+            <input type="text" placeholder="XXXX-XXXX" style="font-family:monospace"
+              value=${approveCode} onInput=${e => setApproveCode(e.target.value)} />
+            <button class="admin-btn" type="submit">${t('device.approve_btn')}</button>
+          </div>
+        </form>
+      </div>
     </div>
   `;
 }
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/crypto.js b/packages/meshbay-hub/src/meshbay_hub/static/crypto.js
index 21bf05d..1ddaa50 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/crypto.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/crypto.js
@@ -321,6 +321,8 @@ async function handshakeProof(gekRaw, role, groupId, nonceClient, nonceNode, bin
 // wrap the group key for a key that came over the wire instead of one fetched
 // from the hub's directory (H3). nonce_node ties it to this connection.
 const JOIN_PREFIX = new TextEncoder().encode('meshbay:join:v1');
+const DEVICE_REQ_PREFIX = new TextEncoder().encode('meshbay:device_req:v1');
+const DEVICE_ADD_PREFIX = new TextEncoder().encode('meshbay:device_add:v1');
 
 function joinTranscript(nodePkB64, groupId, userId, pkEdB64, pkXB64, nonceNode, ts) {
   const enc = new TextEncoder();
@@ -339,6 +341,69 @@ function joinTranscript(nodePkB64, groupId, userId, pkEdB64, pkXB64, nonceNode,
   return out;
 }
 
+/**
+ * Device linking transcripts, mirroring meshbay_common/device.py.
+ *
+ * Two signatures admit a device: the new one proves it holds the keys it is
+ * presenting, and a key the node already pinned countersigns them. The hub can
+ * produce neither — it has stored no user keys since 2026-08-14 — which is what
+ * makes this safe to do without an operator.
+ */
+function deviceRequestTranscript(nodePkB64, userId, pkEdB64, pkXB64, codeHash,
+                                 nonceNode, ts) {
+  const enc = new TextEncoder();
+  const body = _lenPrefixed([
+    enc.encode(nodePkB64), enc.encode(userId), enc.encode(pkEdB64),
+    enc.encode(pkXB64), enc.encode(codeHash), nonceNode, enc.encode(String(ts)),
+  ]);
+  const out = new Uint8Array(DEVICE_REQ_PREFIX.length + body.length);
+  out.set(DEVICE_REQ_PREFIX, 0);
+  out.set(body, DEVICE_REQ_PREFIX.length);
+  return out;
+}
+
+function deviceAddTranscript(nodePkB64, userId, pkEdB64, pkXB64, nonceNode, ts) {
+  const enc = new TextEncoder();
+  const body = _lenPrefixed([
+    enc.encode(nodePkB64), enc.encode(userId), enc.encode(pkEdB64),
+    enc.encode(pkXB64), nonceNode, enc.encode(String(ts)),
+  ]);
+  const out = new Uint8Array(DEVICE_ADD_PREFIX.length + body.length);
+  out.set(DEVICE_ADD_PREFIX, 0);
+  out.set(body, DEVICE_ADD_PREFIX.length);
+  return out;
+}
+
+/**
+ * sha256(code ‖ pk_ed ‖ pk_x), hex — the lookup key for a pending request.
+ *
+ * The keys go in with the code, so the hash identifies *this device asking with
+ * this code* rather than *this code*. That is what stops the node answering an
+ * approver with a substituted key: the approver recomputes this from what they
+ * typed and what they were handed, and a substitution finds nothing. Nothing
+ * here rests on a human comparing digits.
+ */
+async function deviceCodeHash(code, pkEdB64, pkXB64) {
+  const enc = new TextEncoder();
+  const payload = enc.encode([code, pkEdB64, pkXB64].join('\x1f'));
+  const digest = await crypto.subtle.digest('SHA-256', payload);
+  return Array.from(new Uint8Array(digest))
+    .map(b => b.toString(16).padStart(2, '0')).join('');
+}
+
+/** Crockford folding, mirroring roster.normalize_code. */
+function normalizeCode(code) {
+  let out = '';
+  for (const ch of code.toUpperCase()) {
+    if (ch === '-' || ch === ' ' || ch === '\t') continue;
+    if (ch === 'I' || ch === 'L') out += '1';
+    else if (ch === 'O') out += '0';
+    else if (ch === 'U') out += 'V';
+    else out += ch;
+  }
+  return out;
+}
+
 function constantTimeEqual(a, b) {
   if (a.length !== b.length) return false;
   let diff = 0;
@@ -359,4 +424,6 @@ window.MeshBayCrypto = {
   generateGEK, wrapGEK, unwrapGEK, encryptChunk, b64encode, b64decode,
   adminTranscript, handshakeTranscript, handshakeProof, webrtcBinding,
   joinTranscript, verifyNodeSignature, constantTimeEqual,
+  deviceRequestTranscript, deviceAddTranscript, deviceCodeHash,
+  normalizeCode,
 };
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/de.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/de.js
index aaed0d1..5a946f7 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/de.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/de.js
@@ -92,6 +92,19 @@ export default {
   'group.upload': 'Hochladen',
   'group.mkdir': 'Neuer Ordner',
   'group.mkdir_prompt': 'Name des neuen Ordners:',
+  'device.add_title': 'This browser is not linked to this node yet',
+  'device.add_hint': 'Your account is known here, but this browser holds a different key. Approve it from a device already linked — no operator needed.',
+  'device.add_btn': 'Get a linking code',
+  'device.add_show': 'Type this code into a device already linked to this node, within the hour:',
+  'device.mine_title': 'Your devices on this node',
+  'device.mine_hint': 'Each browser or client you use here holds its own key. They are separate from your devices on other nodes.',
+  'device.mine_empty': 'No device is linked here yet.',
+  'device.this_one': 'this one',
+  'device.revoke': 'Remove',
+  'device.revoke_confirm': 'Remove this device? It will lose access to this node until it is linked again.',
+  'device.approve_hint': 'Linking a new device? Enter the code it is showing.',
+  'device.approve_btn': 'Approve',
+  'device.approved': 'Device linked.',
   'group.root_unavailable': '(nicht verfügbar — Laufwerk getrennt)',
   'group.view': 'Ansehen',
   'group.delete': 'Löschen',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/en.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/en.js
index 02532d6..fd2d6ec 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/en.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/en.js
@@ -92,6 +92,19 @@ export default {
   'group.upload': 'Upload',
   'group.mkdir': 'New folder',
   'group.mkdir_prompt': 'Name of the new folder:',
+  'device.add_title': 'This browser is not linked to this node yet',
+  'device.add_hint': 'Your account is known here, but this browser holds a different key. Approve it from a device already linked — no operator needed.',
+  'device.add_btn': 'Get a linking code',
+  'device.add_show': 'Type this code into a device already linked to this node, within the hour:',
+  'device.mine_title': 'Your devices on this node',
+  'device.mine_hint': 'Each browser or client you use here holds its own key. They are separate from your devices on other nodes.',
+  'device.mine_empty': 'No device is linked here yet.',
+  'device.this_one': 'this one',
+  'device.revoke': 'Remove',
+  'device.revoke_confirm': 'Remove this device? It will lose access to this node until it is linked again.',
+  'device.approve_hint': 'Linking a new device? Enter the code it is showing.',
+  'device.approve_btn': 'Approve',
+  'device.approved': 'Device linked.',
   'group.root_unavailable': '(unavailable — the drive is disconnected)',
   'group.view': 'View',
   'group.delete': 'Delete',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/es.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/es.js
index 49bfc1c..e564164 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/es.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/es.js
@@ -90,6 +90,19 @@ export default {
   'group.upload': 'Subir',
   'group.mkdir': 'Nueva carpeta',
   'group.mkdir_prompt': 'Nombre de la nueva carpeta:',
+  'device.add_title': 'This browser is not linked to this node yet',
+  'device.add_hint': 'Your account is known here, but this browser holds a different key. Approve it from a device already linked — no operator needed.',
+  'device.add_btn': 'Get a linking code',
+  'device.add_show': 'Type this code into a device already linked to this node, within the hour:',
+  'device.mine_title': 'Your devices on this node',
+  'device.mine_hint': 'Each browser or client you use here holds its own key. They are separate from your devices on other nodes.',
+  'device.mine_empty': 'No device is linked here yet.',
+  'device.this_one': 'this one',
+  'device.revoke': 'Remove',
+  'device.revoke_confirm': 'Remove this device? It will lose access to this node until it is linked again.',
+  'device.approve_hint': 'Linking a new device? Enter the code it is showing.',
+  'device.approve_btn': 'Approve',
+  'device.approved': 'Device linked.',
   'group.root_unavailable': '(no disponible — la unidad está desconectada)',
   'group.view': 'Ver',
   'group.delete': 'Eliminar',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/fr.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/fr.js
index 1afc5b1..5848f9d 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/fr.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/fr.js
@@ -91,6 +91,19 @@ export default {
   'group.upload': 'Envoyer',
   'group.mkdir': 'Nouveau dossier',
   'group.mkdir_prompt': 'Nom du nouveau dossier :',
+  'device.add_title': 'Ce navigateur n’est pas encore lié à ce nœud',
+  'device.add_hint': 'Votre compte est connu ici, mais ce navigateur détient une autre clé. Approuvez-le depuis un appareil déjà lié — sans passer par l’opérateur.',
+  'device.add_btn': 'Obtenir un code de liaison',
+  'device.add_show': 'Saisissez ce code sur un appareil déjà lié à ce nœud, dans l’heure :',
+  'device.mine_title': 'Vos appareils sur ce nœud',
+  'device.mine_hint': 'Chaque navigateur ou client que vous utilisez ici détient sa propre clé. Ils sont distincts de vos appareils sur les autres nœuds.',
+  'device.mine_empty': 'Aucun appareil lié ici pour le moment.',
+  'device.this_one': 'celui-ci',
+  'device.revoke': 'Retirer',
+  'device.revoke_confirm': 'Retirer cet appareil ? Il perdra l’accès à ce nœud jusqu’à une nouvelle liaison.',
+  'device.approve_hint': 'Vous liez un nouvel appareil ? Saisissez le code qu’il affiche.',
+  'device.approve_btn': 'Approuver',
+  'device.approved': 'Appareil lié.',
   'group.root_unavailable': '(indisponible — le disque est déconnecté)',
   'group.view': 'Afficher',
   'group.delete': 'Supprimer',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/it.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/it.js
index 44b4353..61913e3 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/it.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/it.js
@@ -91,6 +91,19 @@ export default {
   'group.upload': 'Carica',
   'group.mkdir': 'Nuova cartella',
   'group.mkdir_prompt': 'Nome della nuova cartella:',
+  'device.add_title': 'This browser is not linked to this node yet',
+  'device.add_hint': 'Your account is known here, but this browser holds a different key. Approve it from a device already linked — no operator needed.',
+  'device.add_btn': 'Get a linking code',
+  'device.add_show': 'Type this code into a device already linked to this node, within the hour:',
+  'device.mine_title': 'Your devices on this node',
+  'device.mine_hint': 'Each browser or client you use here holds its own key. They are separate from your devices on other nodes.',
+  'device.mine_empty': 'No device is linked here yet.',
+  'device.this_one': 'this one',
+  'device.revoke': 'Remove',
+  'device.revoke_confirm': 'Remove this device? It will lose access to this node until it is linked again.',
+  'device.approve_hint': 'Linking a new device? Enter the code it is showing.',
+  'device.approve_btn': 'Approve',
+  'device.approved': 'Device linked.',
   'group.root_unavailable': '(non disponibile — l’unità è scollegata)',
   'group.view': 'Visualizza',
   'group.delete': 'Elimina',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/ja.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/ja.js
index 33fdee3..aa656ee 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/ja.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/ja.js
@@ -89,6 +89,19 @@ export default {
   'group.upload': 'アップロード',
   'group.mkdir': '新しいフォルダー',
   'group.mkdir_prompt': '新しいフォルダーの名前：',
+  'device.add_title': 'This browser is not linked to this node yet',
+  'device.add_hint': 'Your account is known here, but this browser holds a different key. Approve it from a device already linked — no operator needed.',
+  'device.add_btn': 'Get a linking code',
+  'device.add_show': 'Type this code into a device already linked to this node, within the hour:',
+  'device.mine_title': 'Your devices on this node',
+  'device.mine_hint': 'Each browser or client you use here holds its own key. They are separate from your devices on other nodes.',
+  'device.mine_empty': 'No device is linked here yet.',
+  'device.this_one': 'this one',
+  'device.revoke': 'Remove',
+  'device.revoke_confirm': 'Remove this device? It will lose access to this node until it is linked again.',
+  'device.approve_hint': 'Linking a new device? Enter the code it is showing.',
+  'device.approve_btn': 'Approve',
+  'device.approved': 'Device linked.',
   'group.root_unavailable': '(利用不可 — ドライブが切断されています)',
   'group.view': '表示',
   'group.delete': '削除',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/nl.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/nl.js
index aa0385e..dae903f 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/nl.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/nl.js
@@ -92,6 +92,19 @@ export default {
   'group.upload': 'Uploaden',
   'group.mkdir': 'Nieuwe map',
   'group.mkdir_prompt': 'Naam van de nieuwe map:',
+  'device.add_title': 'This browser is not linked to this node yet',
+  'device.add_hint': 'Your account is known here, but this browser holds a different key. Approve it from a device already linked — no operator needed.',
+  'device.add_btn': 'Get a linking code',
+  'device.add_show': 'Type this code into a device already linked to this node, within the hour:',
+  'device.mine_title': 'Your devices on this node',
+  'device.mine_hint': 'Each browser or client you use here holds its own key. They are separate from your devices on other nodes.',
+  'device.mine_empty': 'No device is linked here yet.',
+  'device.this_one': 'this one',
+  'device.revoke': 'Remove',
+  'device.revoke_confirm': 'Remove this device? It will lose access to this node until it is linked again.',
+  'device.approve_hint': 'Linking a new device? Enter the code it is showing.',
+  'device.approve_btn': 'Approve',
+  'device.approved': 'Device linked.',
   'group.root_unavailable': '(niet beschikbaar — de schijf is losgekoppeld)',
   'group.view': 'Bekijken',
   'group.delete': 'Verwijderen',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/pl.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/pl.js
index e66dd12..65c81ca 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/pl.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/pl.js
@@ -95,6 +95,19 @@ export default {
   'group.upload': 'Wyślij',
   'group.mkdir': 'Nowy folder',
   'group.mkdir_prompt': 'Nazwa nowego folderu:',
+  'device.add_title': 'This browser is not linked to this node yet',
+  'device.add_hint': 'Your account is known here, but this browser holds a different key. Approve it from a device already linked — no operator needed.',
+  'device.add_btn': 'Get a linking code',
+  'device.add_show': 'Type this code into a device already linked to this node, within the hour:',
+  'device.mine_title': 'Your devices on this node',
+  'device.mine_hint': 'Each browser or client you use here holds its own key. They are separate from your devices on other nodes.',
+  'device.mine_empty': 'No device is linked here yet.',
+  'device.this_one': 'this one',
+  'device.revoke': 'Remove',
+  'device.revoke_confirm': 'Remove this device? It will lose access to this node until it is linked again.',
+  'device.approve_hint': 'Linking a new device? Enter the code it is showing.',
+  'device.approve_btn': 'Approve',
+  'device.approved': 'Device linked.',
   'group.root_unavailable': '(niedostępne — dysk jest odłączony)',
   'group.view': 'Podgląd',
   'group.delete': 'Usuń',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/pt-BR.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/pt-BR.js
index 03de040..729a7fc 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/pt-BR.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/pt-BR.js
@@ -92,6 +92,19 @@ export default {
   'group.upload': 'Enviar',
   'group.mkdir': 'Nova pasta',
   'group.mkdir_prompt': 'Nome da nova pasta:',
+  'device.add_title': 'This browser is not linked to this node yet',
+  'device.add_hint': 'Your account is known here, but this browser holds a different key. Approve it from a device already linked — no operator needed.',
+  'device.add_btn': 'Get a linking code',
+  'device.add_show': 'Type this code into a device already linked to this node, within the hour:',
+  'device.mine_title': 'Your devices on this node',
+  'device.mine_hint': 'Each browser or client you use here holds its own key. They are separate from your devices on other nodes.',
+  'device.mine_empty': 'No device is linked here yet.',
+  'device.this_one': 'this one',
+  'device.revoke': 'Remove',
+  'device.revoke_confirm': 'Remove this device? It will lose access to this node until it is linked again.',
+  'device.approve_hint': 'Linking a new device? Enter the code it is showing.',
+  'device.approve_btn': 'Approve',
+  'device.approved': 'Device linked.',
   'group.root_unavailable': '(indisponível — a unidade está desconectada)',
   'group.view': 'Visualizar',
   'group.delete': 'Excluir',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js
index 72995dd..0ff5a49 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js
@@ -88,6 +88,19 @@ export default {
   'group.upload': '上传',
   'group.mkdir': '新建文件夹',
   'group.mkdir_prompt': '新文件夹的名称：',
+  'device.add_title': 'This browser is not linked to this node yet',
+  'device.add_hint': 'Your account is known here, but this browser holds a different key. Approve it from a device already linked — no operator needed.',
+  'device.add_btn': 'Get a linking code',
+  'device.add_show': 'Type this code into a device already linked to this node, within the hour:',
+  'device.mine_title': 'Your devices on this node',
+  'device.mine_hint': 'Each browser or client you use here holds its own key. They are separate from your devices on other nodes.',
+  'device.mine_empty': 'No device is linked here yet.',
+  'device.this_one': 'this one',
+  'device.revoke': 'Remove',
+  'device.revoke_confirm': 'Remove this device? It will lose access to this node until it is linked again.',
+  'device.approve_hint': 'Linking a new device? Enter the code it is showing.',
+  'device.approve_btn': 'Approve',
+  'device.approved': 'Device linked.',
   'group.root_unavailable': '(不可用 — 驱动器已断开连接)',
   'group.view': '查看',
   'group.delete': '删除',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/transport.js b/packages/meshbay-hub/src/meshbay_hub/static/transport.js
index 4ee5810..769114e 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/transport.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/transport.js
@@ -787,6 +787,129 @@ class MeshBayTransport {
     return gekRaw;
   }
 
+  // ── Device linking ─────────────────────────────────────────────────────
+  //
+  // Identity keys are per node, so a browser and a desktop client are two keys
+  // on one account here. A new one is admitted by a key this node already
+  // pinned — never by the hub, which holds no user keys and so cannot
+  // countersign anything. See docs/desktop-client-v1.md §4.
+
+  /**
+   * Ask to be added, and return the code to show the person.
+   *
+   * They read it off this screen and type it into a device already paired with
+   * this node. The code is hashed together with our own keys, so that other
+   * device cannot be handed a substituted key and sign for it by mistake.
+   */
+  async requestDeviceAdd(userId) {
+    if (!this._sessionKeys || !this._sessionKeys.skEdB64) {
+      throw new Error('Identity keys unavailable in this browser — sign in again');
+    }
+    if (!this._nonceNode || !this.nodePk) {
+      throw new Error('Handshake incomplete — reconnect and retry');
+    }
+    const C = window.MeshBayCrypto;
+    const pkEdB64 = await _pkEdFromSk(this._sessionKeys.skEdB64);
+    const pkXB64 = await _pkFromSk(this._sessionKeys.skXB64);
+
+    // 40 bits from the platform CSPRNG, in the same alphabet as a pairing code
+    // so it reads and types the same way.
+    const alphabet = '0123456789ABCDEFGHJKMNPQRSTVWXYZ';
+    const bytes = crypto.getRandomValues(new Uint8Array(8));
+    const raw = Array.from(bytes, b => alphabet[b % alphabet.length]).join('');
+    const code = `${raw.slice(0, 4)}-${raw.slice(4)}`;
+
+    const codeHash = await C.deviceCodeHash(
+      C.normalizeCode(code), pkEdB64, pkXB64);
+    const ts = Math.floor(Date.now() / 1000);
+    const transcript = C.deviceRequestTranscript(
+      this.nodePk, userId, pkEdB64, pkXB64, codeHash, this._nonceNode, ts);
+    const sig = await window.MeshBayKeys.signBytes(
+      this._sessionKeys.skEdB64, transcript);
+
+    const resp = await this._sendAndWait({
+      type: 'device_add_request', v: '0.1',
+      pk_ed25519: pkEdB64, pk_x25519: pkXB64, code_hash: codeHash, ts, sig,
+    });
+    if (resp.type === 'error') throw new Error(resp.detail || 'Refused');
+    return { code, expiresAt: resp.expires_at };
+  }
+
+  /**
+   * Approve a device waiting with this code.
+   *
+   * The node is a mailbox: it is asked for a request matching
+   * sha256(code ‖ keys), and the keys in that hash came from the device that
+   * filed it. A node returning something else produces no match, so there is
+   * nothing to sign and nothing for a person to misread.
+   */
+  async approveDevice(userId, code) {
+    if (!this._sessionKeys || !this._sessionKeys.skEdB64) {
+      throw new Error('Identity keys unavailable in this browser — sign in again');
+    }
+    if (!this._nonceNode || !this.nodePk) {
+      throw new Error('Handshake incomplete — reconnect and retry');
+    }
+    const C = window.MeshBayCrypto;
+    const normalized = C.normalizeCode(code);
+
+    // The code never leaves this browser. The node lists what is pending, each
+    // with the hash the requesting device computed over the code and its own
+    // keys; we recompute and keep the one that matches. A node offering
+    // fabricated keys would have to produce a hash matching sha256(code ‖
+    // fabricated) — and it does not know the code.
+    const listed = await this._sendAndWait({ type: 'device_lookup', v: '0.1' });
+    if (listed.type === 'error') throw new Error(listed.detail || 'Not found');
+
+    let match = null;
+    for (const req of listed.requests || []) {
+      const expect = await C.deviceCodeHash(
+        normalized, req.pk_ed25519, req.pk_x25519);
+      if (expect === req.code_hash) { match = req; break; }
+    }
+    if (!match) {
+      throw new Error('No device is waiting with that code');
+    }
+    return this._countersign(userId, match.code_hash,
+                             match.pk_ed25519, match.pk_x25519);
+  }
+
+  async _countersign(userId, codeHash, pkEdB64, pkXB64) {
+    const C = window.MeshBayCrypto;
+    const ts = Math.floor(Date.now() / 1000);
+    const transcript = C.deviceAddTranscript(
+      this.nodePk, userId, pkEdB64, pkXB64, this._nonceNode, ts);
+    const sig = await window.MeshBayKeys.signBytes(
+      this._sessionKeys.skEdB64, transcript);
+    const resp = await this._sendAndWait({
+      type: 'device_add', v: '0.1',
+      pk_ed25519: pkEdB64, pk_x25519: pkXB64, code_hash: codeHash, ts, sig,
+    });
+    if (resp.type === 'error') throw new Error(resp.detail || 'Refused');
+    return resp;
+  }
+
+  async listDevices() {
+    const resp = await this._sendAndWait({ type: 'device_list', v: '0.1' });
+    if (resp.type === 'error') throw new Error(resp.detail || 'Refused');
+    return { devices: resp.devices || [], pending: resp.pending || 0 };
+  }
+
+  /** Retire a device — a lost laptop. Countersigned like an addition. */
+  async revokeDevice(userId, pkEdB64, pkXB64) {
+    const C = window.MeshBayCrypto;
+    const ts = Math.floor(Date.now() / 1000);
+    const transcript = C.deviceAddTranscript(
+      this.nodePk, userId, pkEdB64, pkXB64, this._nonceNode, ts);
+    const sig = await window.MeshBayKeys.signBytes(
+      this._sessionKeys.skEdB64, transcript);
+    const resp = await this._sendAndWait({
+      type: 'device_revoke', v: '0.1', pk_ed25519: pkEdB64, ts, sig,
+    });
+    if (resp.type === 'error') throw new Error(resp.detail || 'Refused');
+    return resp;
+  }
+
   /**
    * Withdraw our key backup from this node.
    *