`GrpcPort` is a nullable column added by Phase 5. Every insert in the docker-dev
seed is INSERT-if-not-exists — the right shape for a re-runnable seed, but it means
a new nullable column never reaches rows an earlier version of the file created. On
a persisted volume all six rows kept NULL, central found no dial targets, and
`TelemetryDial:Mode=Grpc` connected to nothing. (`AkkaPort` escaped this only
because it is NOT NULL with a default of 4053.)
Seed now backfills `GrpcPort IS NULL AND CreatedBy = 'docker-dev-seed'` to 4056.
NULL only — it must not overwrite a port an operator set deliberately on a
long-lived dev volume, and NULL is the unambiguous "predates the column" marker.
Deliberately NOT doing the suggested EF data migration for real deployments. The
correct value is each node's own `Telemetry:GrpcListenPort`, which is
per-deployment configuration the database cannot derive; a migration could only
invent one, and a WRONG dial target is worse than the NULL the dialer already skips
explicitly with a throttled warning. The rig can be backfilled because there the
port is fixed by docker-compose.yml and therefore actually knowable.
`docs/Telemetry.md` gains an upgrade section stating the prerequisite, the symptoms
(the throttled skip log, LISTEN with no ESTABLISHED, the pill never going live) and
the UPDATE to run before flipping any node to Grpc — plus why there is no migration.
Joseph Doherty
8b7ea3213d