(dbx) where
  [1] __lwp_kill(0x1, 0x6, 0xfffffe88d2d96ac0, 0xfffffd7ffeb827be, 0x4b, 0x0), at 0xfffffd7ffeb81eca
  [2] _thr_kill(0x0, 0x0, 0x0, 0x0, 0x0, 0x0), at 0xfffffd7ffeb7a7d3
  [3] raise(0x0, 0x0, 0x0, 0x0, 0x0, 0x0), at 0xfffffd7ffeb26fe9
  [4] abort(0x0, 0x0, 0x0, 0x0, 0x0, 0x0), at 0xfffffd7ffeb05f60
=>[5] default_fatal_finish(type = LOG_TYPE_PANIC, status = 0), line 201 in "failures.c"
  [6] i_internal_fatal_handler(ctx = 0xfffffd7fffdff9e8, format = 0x491710 "file %s: line %d: assertion failed: (%s)", args = 0xfffffd7fffdff9d0), line 670 in "failures.c"
  [7] i_panic(format = 0x491710 "file %s: line %d: assertion failed: (%s)", ... = 0x45d783, ...), line 275 in "failures.c"
  [8] client_check_command_hangs(client = 0x4d1650), line 828 in "imap-client.c"
  [9] client_continue_pending_input(client = 0x4d1650), line 897 in "imap-client.c"
  [10] client_output(client = 0x4d1650), line 1213 in "imap-client.c"
  [11] stream_send_io(fstream = 0x4c9460), line 482 in "ostream-file.c"
  [12] io_loop_call_io(io = 0x5c64d0), line 564 in "ioloop.c"
  [13] io_loop_handler_run_internal(ioloop = 0x4b3d20), line 211 in "ioloop-poll.c"
  [14] io_loop_handler_run(ioloop = 0x4b3d20), line 612 in "ioloop.c"
  [15] io_loop_run(ioloop = 0x4b3d20), line 588 in "ioloop.c"
  [16] master_service_run(service = 0x4b23e0, callback = 0x482590 = &`imap`main.c`client_connected(struct master_service_connection *conn)), line 640 in "master-service.c"
  [17] main(argc = 1, argv = 0xfffffd7fffdffcb8), line 460 in "main.c"

(dbx) frame 8
Current function is client_check_command_hangs
  828                           i_assert(client->io != NULL);

(dbx) print *client
*client = {
    prev                       = (nil)
    next                       = (nil)
    v                          = {
        state_export = 0x4795a0 = &imap_state_export_base()
        state_import = 0x47b880 = &imap_state_import_base()
        destroy      = 0x45ba50 = &`imap`imap-client.c`client_default_destroy(struct client *client, const char *reason)
    }
    session_id                 = 0x4d17f8 "M0DilFc04spQ2Cr8"
    userdb_fields              = 0x4d1a20
    fd_in                      = 7
    fd_out                     = 7
    io                         = (nil)
    input                      = 0x4c9320
    output                     = 0x4c94f0
    to_idle                    = 0x4c95a0
    to_idle_output             = 0x54c470
    to_delayed_input           = (nil)
    pool                       = 0x4d1630
    service_user               = 0x4be1c0
    set                        = 0x4bee38
    lda_set                    = 0x4beec8
    capability_string          = 0x4d1870
    user                       = 0x4c9f10
    mailbox                    = 0x4d4680
    keywords                   = {
        names          = 0x506118
        announce_count = 10U
    }
    sync_counter               = 131U
    messages_count             = 1989U
    recent_count               = 2U
    uidvalidity                = 1183546861U
    enabled_features           = MAILBOX_FEATURE_CONDSTORE
    last_input                 = 1464925732
    last_output                = 1464925732
    bad_counter                = 0
    free_parser                = (nil)
    command_pool               = 0x4d1e40
    command_queue              = 0x5c7620
    command_queue_size         = 3U
    sync_last_full_modseq      = 642109U
    highest_fetch_modseq       = 642130U
    fetch_hdr_count            = 2195U
    fetch_body_count           = 854U
    fetch_hdr_bytes            = 1673864U
    fetch_body_bytes           = 46240644U
    deleted_count              = 0
    expunged_count             = 0
    trashed_count              = 0
    search_saved_uidset        = {
        arr          = {
            buffer       = (nil)
            element_size = 0
        }
        v            = (nil)
        v_modifiable = (nil)
    }
    search_updates             = {
        arr          = {
            buffer       = (nil)
            element_size = 0
        }
        v            = (nil)
        v_modifiable = (nil)
    }
    notify_ctx                 = (nil)
    notify_uidnext             = 214266U
    input_lock                 = 0x5c7620
    output_cmd_lock            = 0x5c6db0
    mailbox_change_lock        = (nil)
    urlauth_ctx                = (nil)
    module_contexts            = {
        arr          = {
            buffer       = 0x4d1810
            element_size = 8U
        }
        v            = 0x4d1810
        v_modifiable = 0x4d1810
    }
   sync_seen_deletes          = 0
    disconnected               = 0
    destroyed                  = 0
    handling_input             = 0
    syncing                    = 0
    id_logged                  = 1U
    mailbox_examined           = 0
    anvil_sent                 = 1U
    tls_compression            = 0
    input_skip_line            = 1U
    modseqs_sent_since_sync    = 0
    notify_immediate_expunges  = 0
    notify_count_changes       = 1U
    notify_flag_changes        = 1U
    imap_metadata_enabled      = 0
    nonpermanent_modseqs       = 0
    state_import_bad_idle_done = 0
    state_import_idle_continue = 0
}
(dbx)