`seat <name> --to <node>/<module>` makes one assignment the holder of a seat in
the same write that removes the previous one. The row is new (migration 0039);
without one, the resolver derives the holder as it always did — the sole eligible
assignment, two refused — so nothing changes for a mesh that never hands a seat
over. With one, the recorded assignment holds and any other whose module could
hold the seat is eligible and silent: not refused, not holding. That is what lets
the next holder run beside the current one until the switch (hq design 26, design
28 task 5.3, ADR 0131).
Why: the controller finds its own bus through a seat, and the day that seat was
left with nobody in it — because two eligible holders could not coexist and the
old one's claim was taken away — the control plane looped for two hours while
every service stayed up. A handover that is never empty in between is the fix,
not a workaround for it.
`CanHold` is the one judgement of whether a module may hold a seat — claims it at
its scope, provides what it delivers, against the store's row — shared by
registration and the handover so they cannot drift apart. The holding belongs to
the assignment and goes when it does, so a seat never points at nothing running.
Tests: the resolver with and without a record, on the same and another machine,
under a former name; the store's row replaced not added, refused for an
unassigned target, removed with its assignment; CanHold's four answers and that
they follow the store. Full suite green against a real NATS and store.
Phase 1 made the set data; a rename still broke every reference to the old
name. This adds the stable identity: a seat's canonical name changes and its
old name becomes an alias that resolves to it forever. SeatNamed and the holder
and display matching resolve a name (former or current) to its seat, so a
manifest's claim, a held record, the git-seat lookup and the build machine's
embedded set all go on working unchanged after a rename. seat_alias table
(migration 0035), inventory Aliases/RenameSeat, openInventory loads them, and a
'seat rename <from> <to>' command does the whole thing — one operation, no
rebuild, no re-registration, no freeze. Behaviour-neutral until a seat is
renamed. Validated against postgres.
The seat set was a Go slice compiled into the controller and referenced by
name everywhere, so changing it meant a rebuild and a freeze-prone deploy. It
is now a table: catalogue keeps the shipped set as defaultSeats (the seed and
the fallback) and a loadable working set; inventory adds the seat table
(migration 0034), Seats to read it, and SeedSeats to fill it idempotently
without overwriting an operator's edit; migrate seeds it; openInventory loads
it, and an empty or unreadable table leaves the compiled defaults in force so
it can never brick the control plane's boot.
Behaviour-neutral: the seeded table equals the defaults. Phase 2 (reference by
a stable id so a rename touches no manifest or code, and the builder reads the
set from the mesh) follows.
jschoubben