Deletion of switch port settings is incomplete and leaves Nexus confused

While doing an unrelated test on dublin, I created a dummy link and switch port settings for switch 1, qsfp 3 via the CLI:

% oxide system networking link add --rack c88542d0-b11f-44a7-939c-9444db5d8dd5 --switch switch1 --port qsfp3 --speed 100g
% oxide system hardware switch-port apply-settings --rack-id c88542d0-b11f-44a7-939c-9444db5d8dd5 --switch-location switch1 --port qsfp3 --port-settings switch1-qsfp3
% oxide system networking switch-port-settings list
[
  {
    "description": "initial uplink configuration",
    "id": "64ca3018-19a8-4425-a189-06e80708c58e",
    "name": "default-uplink0",
    "time_created": "2026-03-06T13:58:12.541313Z",
    "time_modified": "2026-03-06T13:58:12.541313Z"
  }, {
    "description": "initial uplink configuration",
    "id": "4e947e91-4a65-4036-bfdb-3a6523923487",
    "name": "default-uplink1",
    "time_created": "2026-03-06T13:58:12.811138Z",
    "time_modified": "2026-03-06T13:58:12.811138Z"
  }, {
    "description": "",
    "id": "d4a022b9-7760-482c-9501-746942e0183a",
    "name": "switch1-qsfp3",
    "time_created": "2026-03-06T16:02:04.498730Z",
    "time_modified": "2026-03-06T16:02:04.498730Z"
  }
]

Then I tried to delete the new settings, which appeared to work:

% oxide system networking switch-port-settings delete --port-settings d4a022b9-7760-482c-9501-746942e0183a
% oxide system networking switch-port-settings list
[
  {
    "description": "initial uplink configuration",
    "id": "64ca3018-19a8-4425-a189-06e80708c58e",
    "name": "default-uplink0",
    "time_created": "2026-03-06T13:58:12.541313Z",
    "time_modified": "2026-03-06T13:58:12.541313Z"
  }, {
    "description": "initial uplink configuration",
    "id": "4e947e91-4a65-4036-bfdb-3a6523923487",
    "name": "default-uplink1",
    "time_created": "2026-03-06T13:58:12.811138Z",
    "time_modified": "2026-03-06T13:58:12.811138Z"
  }
]

However, a new RackNetworkConfig was not pushed to sled-agent as a result of this operation. Looking at the Nexus logs, the sync_switch_configuration bg task was emitting this warning:

16:26:25.373Z ERRO e89b2e91-5645-45c2-b76d-4eaa4ce8b364 (ServerContext): failed to get switch port settings
    background_task = switch_port_config_manager
    error = Object (of type ById(d4a022b9-7760-482c-9501-746942e0183a)) not found: switch-port-settings
    file = nexus/src/app/background/tasks/sync_switch_configuration.rs:216
    rack_id = c88542d0-b11f-44a7-939c-9444db5d8dd5
    switch_port_settings_id = d4a022b9-7760-482c-9501-746942e0183a
16:26:25.373Z ERRO e89b2e91-5645-45c2-b76d-4eaa4ce8b364 (ServerContext): failed to generate changeset for switchport settings
    background_task = switch_port_config_manager
    error = {"error":"failed to get switch port settings: Object (of type ById(d4a022b9-7760-482c-9501-746942e0183a)) not found: switch-port-settings"}
    file = nexus/src/app/background/tasks/sync_switch_configuration.rs:426
    rack_id = c88542d0-b11f-44a7-939c-9444db5d8dd5

It looks like it's trying to look up the settings we deleted. I think that's because the switch_port table still refers to it:

root@[fd0d:afdc:bd0e:103::3]:32221/omicron> select * from switch_port where switch_location = 'switch1' and port_name = 'qsfp3';
                   id                  |               rack_id                | switch_location | port_name |           port_settings_id
---------------------------------------+--------------------------------------+-----------------+-----------+---------------------------------------
  9bf5c56b-4fcc-48ef-81b2-78fe852860e1 | c88542d0-b11f-44a7-939c-9444db5d8dd5 | switch1         | qsfp3     | d4a022b9-7760-482c-9501-746942e0183a
(1 row)

even though it's not present in switch_port_settings:

root@[fd0d:afdc:bd0e:103::3]:32221/omicron> select * from switch_port_settings;
                   id                  |      name       |         description          |         time_created          |         time_modified         | time_deleted
---------------------------------------+-----------------+------------------------------+-------------------------------+-------------------------------+---------------
  4e947e91-4a65-4036-bfdb-3a6523923487 | default-uplink1 | initial uplink configuration | 2026-03-06 13:58:12.811138+00 | 2026-03-06 13:58:12.811138+00 | NULL
  64ca3018-19a8-4425-a189-06e80708c58e | default-uplink0 | initial uplink configuration | 2026-03-06 13:58:12.541313+00 | 2026-03-06 13:58:12.541313+00 | NULL
(2 rows)

(Is it surprising it was hard deleted from switch_port_settings when we have a time_deleted column? The latter implies we'd soft delete.)

At a surface level, I think deleting a switch_port_settings row also needs to clear the fake-foreign-key in switch_port. But happy to defer to others with more expertise - there's a lot going on here that for which I don't have context.

Start with nexus/src/app/background/tasks/sync_switch_configuration.rs, especially the reported lines around 216 and 426, then trace deletion of switch-port settings and the switch_port reference. Reproduce the CLI sequence and verify that deleting settings no longer leaves a missing reference; done means a new RackNetworkConfig is pushed to sled-agent without the Nexus warning.