`ensureRegistered` requires forcing for the appservice bot user.

[Gnuxie]

Context, trying to use ensureRegistered followed by setDisplayName doesn't register the profile in Synapse.

2026-04-16 09:48:05,148 - synapse.http.server - 147 - ERROR - PUT-389 - Failed handle request via 'ProfileFieldRestServlet': <SynapseRequest at 0x7ff078e142d0 method='PUT' uri='/_matrix/client/v3/profile/%40draupnir-moderation%3Alocalhost%3A9999/displayname' clientproto='HTTP/1.0' s
ite='8008'>
Traceback (most recent call last):
  File "/usr/local/lib/python3.13/site-packages/synapse/http/server.py", line 335, in _async_render_wrapper
    callback_return = await self._async_render(request)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/synapse/http/server.py", line 576, in _async_render
    callback_return = await raw_callback_return
                      ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/synapse/rest/client/profile.py", line 208, in on_PUT
    await self.profile_handler.set_displayname(
        user, requester, new_value, by_admin=is_admin, propagate=propagate
    )
  File "/usr/local/lib/python3.13/site-packages/synapse/handlers/profile.py", line 255, in set_displayname
    await self.store.set_profile_displayname(target_user, displayname_to_set)
  File "/usr/local/lib/python3.13/site-packages/synapse/storage/databases/main/profile.py", line 402, in set_profile_displayname
    await self.db_pool.runInteraction(
        "set_profile_displayname", set_profile_displayname
    )
  File "/usr/local/lib/python3.13/site-packages/synapse/storage/database.py", line 1015, in runInteraction
    return await delay_cancellation(_runInteraction())
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/twisted/internet/defer.py", line 1187, in __iter__
    yield self
  File "/usr/local/lib/python3.13/site-packages/twisted/internet/defer.py", line 1853, in _inlineCallbacks
    result = context.run(
        cast(Failure, result).throwExceptionIntoGenerator, gen
    )
  File "/usr/local/lib/python3.13/site-packages/twisted/python/failure.py", line 467, in throwExceptionIntoGenerator
    return g.throw(self.value.with_traceback(self.tb))
           ~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/synapse/storage/database.py", line 981, in _runInteraction
    result: R = await self.runWithConnection(
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<11 lines>...
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/synapse/storage/database.py", line 1117, in runWithConnection
    return await make_deferred_yieldable(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        self._db_pool.runWithConnection(inner_func, *args, **kwargs)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/twisted/internet/defer.py", line 1187, in __iter__
    yield self
  File "/usr/local/lib/python3.13/site-packages/twisted/python/threadpool.py", line 269, in inContext
    result = inContext.theWork()  # type: ignore[attr-defined]
  File "/usr/local/lib/python3.13/site-packages/twisted/python/threadpool.py", line 285, in <lambda>
    inContext.theWork = lambda: context.call(  # type: ignore[attr-defined]
                                ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        ctx, func, *args, **kw
        ^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/twisted/python/context.py", line 117, in callWithContext
    return self.currentContext().callWithContext(ctx, func, *args, **kw)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/twisted/python/context.py", line 82, in callWithContext
    return func(*args, **kw)
  File "/usr/local/lib/python3.13/site-packages/twisted/enterprise/adbapi.py", line 282, in _runWithConnection
    result = func(conn, *args, **kw)
  File "/usr/local/lib/python3.13/site-packages/synapse/storage/database.py", line 1110, in inner_func
    return func(db_conn, *args, **kwargs)
  File "/usr/local/lib/python3.13/site-packages/synapse/storage/database.py", line 819, in new_transaction
    r = func(cursor, *args, **kwargs)
  File "/usr/local/lib/python3.13/site-packages/synapse/storage/databases/main/profile.py", line 388, in set_profile_displayname
    self._check_profile_size(
    ~~~~~~~~~~~~~~~~~~~~~~~~^
        txn, user_id, ProfileFields.DISPLAYNAME, new_displayname
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/synapse/storage/databases/main/profile.py", line 354, in _check_profile_size
    (row[0] - 1 if row[0] else 0)
                   ~~~^^^
TypeError: 'NoneType' object is not subscriptable
2026-04-16 09:48:05,151 - synapse.access.http.8008 - 643 - INFO - PUT-389 - ::ffff:10.10.0.1 - 8008 - {@draupnir-moderation:localhost:9999} Processed request: 0.003sec/0.000sec ru=(0.002sec, 0.000sec) db=(0.000sec/0.000sec/1) 55B 500 "PUT /_matrix/client/v3/profile/%40draupnir-moder
ation%3Alocalhost%3A9999/displayname HTTP/1.0" "-" [0 dbevts]

has to be worked around by using ensureRegistered(true)