smoketest_config.json sets "discovery": null, so the simulator never appears in an mDNS browse

[markzporter]

What happens

Started from config/smoketest_config.json, the connector's SiLA server comes
up and serves normally — it answers a direct exploration on 127.0.0.1:50051
with all 14 implemented features — but it never registers an mDNS service, so
no SiLA discovery client can find it.

Why

config/smoketest_config.json sets:

"discovery": null

The CDK declares discovery: DiscoveryConfig | None
(unitelabs/cdk/config/connector_base_config.py:221, class at :205), so
null disables the network announcement entirely.

The OT-2 connector's equivalent config
(sila2_ot2/opentrons-ot2/config/ot2_smoketest_config.json) instead sets:

"discovery": { "ip_version": "ipv4", "network_interfaces": [] }

and that simulator is discovered normally. The two configs are otherwise
structurally identical, including hostname on loopback — so this is the one
key that differs, not a version or bind-address effect. For reference, the
versions in each venv are near-identical too: flex unitelabs-cdk 0.9.0 /
unitelabs-sila 0.7.6, ot2 unitelabs-cdk 0.9.0 / unitelabs-sila 0.7.5.

Reproduce

connector start --app unitelabs.opentrons_flex:create_app \
  -cfg config/smoketest_config.json -vvv

Then browse, e.g. with the uoroboros SiLA toolkit:

uoroboros sila discover                 # the Flex is absent
uoroboros sila explore 127.0.0.1:50051  # works: "Opentrons Flex Smoketest", 14 features

dns-sd -B _sila._tcp local shows no announcement from the connector.

Impact

Any discovery-based client sees the lab one instrument short. With the OT-2 and
i2rt YAM simulators running alongside, an mDNS browse returns 2 of 3, and the
Flex can only be reached by typing its host and port. This also affects the
i2rt-yam-style pattern of locating a connector by announced name rather than
a configured address.

Suggested fix

Enable discovery in the smoketest config, matching the OT-2's block:

-  "discovery": null,
+  "discovery": {
+    "ip_version": "ipv4",
+    "network_interfaces": []
+  },

If null is deliberate — to keep a simulator from advertising itself on a lab
network — then it would help to say so in the file, and perhaps ship a second
config (e.g. smoketest_discoverable_config.json) for the discovery case, so
local testing does not need an override.