fix: skip Authorization header when federation key is empty

Empty remote_instances[].key produced 'Bearer ' (illegal header value)
causing httpx to reject the request entirely. Fix: only include the
Authorization header when the key is non-empty. Remotes without keys
still work if their auth allows it (e.g., localhost bypass).

Fixes all 5 sites: fetch_remote GET, connect POST, bell/clear POST,
create-session POST, and WebSocket proxy additional_headers.

muxplex/main.py

@@ -760,7 +760,9 @@ async def federation_terminal_ws_proxy(websocket: WebSocket, remote_id: int) ->
         async with websockets.connect(
             ws_url,
             subprotocols=[Subprotocol("tty")],
-            additional_headers={"Authorization": f"Bearer {remote_key}"},
+            additional_headers={"Authorization": f"Bearer {remote_key}"}
+            if remote_key
+            else {},
         ) as remote_ws:
 
             async def client_to_remote() -> None:
@@ -926,7 +928,7 @@ async def federation_sessions(request: Request) -> list[dict]:
         try:
             resp = await http_client.get(
                 f"{url.rstrip('/')}/api/sessions",
-                headers={"Authorization": f"Bearer {key}"},
+                headers={"Authorization": f"Bearer {key}"} if key else {},
             )
             if resp.status_code in (401, 403):
                 return [
@@ -1026,7 +1028,7 @@ async def federation_connect(
     try:
         resp = await http_client.post(
             url,
-            headers={"Authorization": f"Bearer {remote_key}"},
+            headers={"Authorization": f"Bearer {remote_key}"} if remote_key else {},
         )
         resp.raise_for_status()
         return resp.json()
@@ -1072,7 +1074,7 @@ async def federation_bell_clear(
     try:
         resp = await http_client.post(
             url,
-            headers={"Authorization": f"Bearer {remote_key}"},
+            headers={"Authorization": f"Bearer {remote_key}"} if remote_key else {},
         )
         resp.raise_for_status()
         return resp.json()
@@ -1119,7 +1121,7 @@ async def federation_create_session(
     try:
         resp = await http_client.post(
             url,
-            headers={"Authorization": f"Bearer {remote_key}"},
+            headers={"Authorization": f"Bearer {remote_key}"} if remote_key else {},
             json={"name": payload.name},
         )
         resp.raise_for_status()

muxplex/tests/test_api.py

@@ -2624,3 +2624,57 @@ def test_federation_create_session_returns_502_when_remote_returns_error(
 
     response = client.post("/api/federation/0/sessions", json={"name": "new-session"})
     assert response.status_code == 502
+
+
+# ---------------------------------------------------------------------------
+# Federation Authorization header safety — guard against empty key
+# ---------------------------------------------------------------------------
+
+
+def test_federation_auth_headers_guard_empty_key():
+    """Every federation Authorization header construction must guard against empty key.
+
+    An empty remote_instances[].key produces 'Bearer ' (trailing space, empty
+    token).  httpx rejects that with "Illegal header value b'Bearer '" which
+    silently makes the remote appear unreachable.
+
+    The fix: every site that constructs the header must use the pattern
+        headers={"Authorization": f"Bearer {key}"} if key else {}
+    or an equivalent conditional, so an empty key simply omits the header.
+
+    This is a source-inspection test — it catches regressions without spinning
+    up a live server.
+    """
+    import inspect
+
+    import muxplex.main as main_mod
+
+    source = inspect.getsource(main_mod)
+
+    # Collect every line that constructs an Authorization Bearer header (not
+    # comment or docstring lines — we only care about executable code lines).
+    offending: list[str] = []
+    for line in source.splitlines():
+        stripped = line.strip()
+        # Skip comment and docstring lines
+        if (
+            stripped.startswith("#")
+            or stripped.startswith('"""')
+            or stripped.startswith("'\"'\"'")
+        ):
+            continue
+        # Match lines that build the header dict value
+        if (
+            '"Authorization"' in stripped
+            and "Bearer" in stripped
+            and 'f"Bearer' in stripped
+        ):
+            # Must have an inline `if` guard — e.g. `{...} if key else {}`
+            if " if " not in stripped:
+                offending.append(stripped)
+
+    assert not offending, (
+        "Unguarded federation Bearer header(s) found in main.py — "
+        "use `{...} if key else {}` to skip the header when key is empty:\n"
+        + "\n".join(f"  {line}" for line in offending)
+    )